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+The Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: A Brief History of Element Discovery, Synthesis, and Analysis
+
+Author: Glen W. Watson
+
+Release Date: March 13, 2010 [EBook #31624]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELEMENT DISCOVERY ***
+
+
+
+
+Produced by Mark C. Orton, Erica Pfister-Altschul and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+[Transcriber's Notes: The following errors are noted, but have not been
+corrected:
+
+    Page 17, footnote: "plutomium" should be "plutonium"
+    Page 8: "knowns" should be "knows"
+
+In element names, {} represents subscripted numbers and <> represents
+superscripted numbers. Readers may also refer to the HTML version of the
+text, in which super and subscripted numbers are represented visually.
+
+Italic emphasis is indicated by surrounding the word with _underscores_.
+
+Greek letters in the original text are marked in brackets, e. g. [alpha]
+or [gamma].
+
+Table I (THE TRANSURANIUM ELEMENTS) has been moved from pages 12-13, in
+the middle of the book, to the end of the text.]
+
+
+
+
+    A Brief History
+    of
+    ELEMENT DISCOVERY,
+    SYNTHESIS, and ANALYSIS
+
+
+    Glen W. Watson
+    September 1963
+
+    [Illustration]
+
+    LAWRENCE RADIATION LABORATORY
+    University of California
+    Berkeley and Livermore
+
+
+    Operating under contract with the
+    United States Atomic Energy Commission
+
+[Illustration: Radioactive elements: alpha particles from a speck of
+radium leave tracks on a photographic emulsion. (Occhialini and Powell,
+1947)]
+
+
+
+
+A BRIEF HISTORY OF ELEMENT DISCOVERY, SYNTHESIS, AND ANALYSIS
+
+
+It is well known that the number of elements has grown from four in the
+days of the Greeks to 103 at present, but the change in methods needed
+for their discovery is not so well known. Up until 1939, only 88
+naturally occurring elements had been discovered. It took a dramatic
+modern technique (based on Ernest O. Lawrence's Nobel-prize-winning atom
+smasher, the cyclotron) to synthesize the most recently discovered
+elements. Most of these recent discoveries are directly attributed to
+scientists working under the Atomic Energy Commission at the University
+of California's Radiation Laboratory at Berkeley.
+
+But it is apparent that our present knowledge of the elements stretches
+back into history: back to England's Ernest Rutherford, who in 1919
+proved that, occasionally, when an alpha particle from radium strikes a
+nitrogen atom, either a proton or a hydrogen nucleus is ejected; to the
+Dane Niels Bohr and his 1913 idea of electron orbits; to a once unknown
+Swiss patent clerk, Albert Einstein, and his now famous theories; to
+Poland's Marie Curie who, in 1898, with her French husband Pierre
+laboriously isolated polonium and radium; back to the French scientist
+H. A. Becquerel, who first discovered something he called a "spontaneous
+emission of penetrating rays from certain salts of uranium"; to the
+German physicist W. K. Roentgen and his discovery of x rays in 1895; and
+back still further.
+
+During this passage of scientific history, the very idea of "element"
+has undergone several great changes.
+
+The early Greeks suggested earth, air, fire, and water as being the
+essential material from which all others were made. Aristotle considered
+these as being combinations of four properties: hot, cold, dry, and
+moist (see Fig. 1).
+
+[Illustration: Fig. 1. The elements as proposed by the early Greeks.]
+
+Later, a fifth "essence," ether, the building material of the heavenly
+bodies was added.
+
+Paracelsus (1493-1541) introduced the three alchemical symbols salt,
+sulfur, and mercury. Sulfur was the principle of combustability, salt
+the fixed part left after burning (calcination), and mercury the
+essential part of all metals. For example, gold and silver were
+supposedly different combinations of sulfur and mercury.
+
+Robert Boyle in his "Sceptical Chymist" (1661) first defined the word
+element in the sense which it retained until the discovery of
+radioactivity (1896), namely, a form of matter that could not be split
+into simpler forms.
+
+The first discovery of a true element in historical time was that of
+phosphorus by Dr. Brand of Hamburg, in 1669. Brand kept his process
+secret, but, as in modern times, knowledge of the element's existence
+was sufficient to let others, like Kunkel and Boyle in England, succeed
+independently in isolating it shortly afterward.
+
+As in our atomic age, a delicate balance was made between the
+"light-giving" (desirable) and "heat-giving" (feared) powers of a
+discovery. An early experimenter was at first "delighted with the white,
+waxy substance that glowed so charmingly in the dark of his laboratory,"
+but later wrote, "I am not making it any more for much harm may come of
+it."
+
+Robert Boyle wrote in 1680 of phosphorus, "It shone so briskly and lookt
+so oddly that the sight was extreamly pleasing, having in it a mixture
+of strangeness, beauty and frightfulness."
+
+These words describe almost exactly the impressions of eye witnesses of
+the first atom bomb test at Alamagordo, New Mexico, July 16, 1945.
+
+For the next two and three-quarters centuries the chemists had much fun
+and some fame discovering new elements. Frequently there was a long
+interval between discovery and recognition. Thus Scheele made chlorine
+in 1774 by the action of "black manganese" (manganese dioxide) on
+concentrated muriatic acid (hydrochloric acid), but it was not
+recognized as an element till the work of Davy in 1810.
+
+Occasionally the development of a new technique would lead to the "easy"
+discovery of a whole group of new elements. Thus Davy, starting in 1807,
+applied the method of electrolysis, using a development of Volta's pile
+as a source of current; in a short time he discovered aluminum, barium,
+boron, calcium, magnesium, potassium, sodium, and strontium.
+
+The invention of the spectroscope by Bunsen and Kirchhoff in 1859
+provided a new tool which could establish the purity of substances
+already known and lead to the discovery of others. Thus, helium was
+discovered in the sun's spectrum by Jansen and isolated from uranite by
+Ramsay in 1895.
+
+The discovery of radioactivity by Becquerel in 1896 (touched off by
+Roentgen's discovery of x rays the year before) gave an even more
+sensitive method of detecting the presence or absence of certain kinds
+of matter. It is well known that Pierre and Marie Curie used this
+new-found radioactivity to identify the new elements polonium and
+radium. Compounds of these new elements were obtained by patient
+fractional recrystallization of their salts.
+
+The "explanation" of radioactivity led to the discovery of isotopes by
+Rutherford and Soddy in 1914, and with this discovery a revision of our
+idea of elements became necessary. Since Boyle, it had been assumed that
+all atoms of the individual elements were identical and unlike any
+others, and could not be changed into anything simpler. Now it became
+evident that the atoms of radioactive elements were constantly changing
+into other elements, thereby releasing very large amounts of energy, and
+that many different forms of the same element (lead was the first
+studied) were possible. We now think of an element as a form of matter
+in which all atoms have the same nuclear charge.
+
+The human mind has always sought order and simplification of the
+external world; in chemistry the fruitful classifications were
+Dobereiner's Triads (1829), Newland's law of octaves (1865), and
+Mendeleev's periodic law (1869). The chart expressing this periodic law
+seemed to indicate the maximum extent of the elements and gave good
+hints "where to look for" and "the probable properties of" the remaining
+ones (see Fig. 2).
+
+By 1925, all but four of the slots in the 92-place file had been filled.
+The vacancies were at 43, 61, 85, and 87.
+
+[Illustration: Fig. 2. Periodic chart of the elements (1963)]
+
+Workers using traditional analytical techniques continued to search for
+these elements, but their efforts were foredoomed to failure. None of
+the nuclei of the isotopes of elements 43, 61, 85, and 87 are stable;
+hence weighable quantities of them do not exist in nature, and new
+techniques had to be developed before we could really say we had
+"discovered" them.
+
+In 1919, Rutherford accomplished scientifically what medieval alchemists
+had failed to do with "magic" experiments and other less sophisticated
+techniques. It wasn't gold (the goal of the alchemists) he found but
+something more valuable with even greater potential for good and evil: a
+method of transmuting one element into another. By bombarding nitrogen
+nuclei with alpha particles from radium, he found that nitrogen was
+changed into oxygen.
+
+The process for radioactive transmutation is somewhat like a common
+chemical reaction. An alpha particle, which has the same charge (+2) and
+atomic mass (4) as a helium nucleus, penetrates the repulsive forces of
+the nitrogen nucleus and deposits one proton and one neutron; this
+changes the nitrogen atom into an oxygen atom. The reaction is written
+
+    {7}N<14> + {2}He<4> --> {1}H<1> + {8}O<17>.
+
+The number at the lower left of each element symbol in the above
+reaction is the proton number. This number determines the basic chemical
+identity of an atom, and it is this number scientists must change before
+one element can be transformed into another. The common way to
+accomplish this artificially is by bombarding nuclei with nuclear
+projectiles.
+
+Rutherford used naturally occurring alpha particles from radium as his
+projectiles because they were the most effective he could then find. But
+these natural alpha particles have several drawbacks: they are
+positively charged, like the nucleus itself, and are therefore more or
+less repulsed depending on the proton number of the element being
+bombarded; they do not move fast enough to penetrate the nuclei of
+heavier elements (those with many protons); and, for various other
+reasons (some of them unexplained), are inefficient in breaking up the
+nucleus. It is estimated that only 1 out of 300,000 of these alpha
+particles will react with nitrogen.
+
+Physicists immediately began the search for artificial means to
+accelerate a wider variety of nuclear particles to high energies.
+
+Protons, because they have a +1 charge rather than the +2 charge of the
+alpha particles, are repulsed less strongly by the positive charge on
+the nucleus, and are therefore more useful as bombarding projectiles. In
+1929, E. T. S. Walton and J. D. Cockcroft passed an electric discharge
+through hydrogen gas, thereby removing electrons from the hydrogen atom;
+this left a beam of protons (i. e., hydrogen ions), which was then
+accelerated by high voltages. This Cockcroft-Walton voltage multiplier
+accelerated the protons to fairly high energies (about 800,000 electron
+volts), but the protons still had a plus charge and their energies were
+still not high enough to overcome the repulsive forces (Coulombic
+repulsion) of the heavier nuclei.
+
+A later development, the Van de Graaff electrostatic generator, produced
+a beam of hydrogen ions and other positively charged ions, and electrons
+at even higher energies. An early model of the linear accelerator also
+gave a beam of heavy positive ions at high energies. These were the next
+two instruments devised in the search for efficient bombarding
+projectiles. However, the impasse continued: neither instrument allowed
+scientists to crack the nuclei of the heavier elements.
+
+Ernest O. Lawrence's cyclotron, built in 1931, was the first device
+capable of accelerating positive ions to the very high energies needed.
+Its basic principle of operation is not difficult to understand. A
+charged particle accelerated in a cyclotron is analogous to a ball being
+whirled on a string fastened to the top of a pole. A negative electric
+field attracts the positively charged particle (ball) towards it and
+then switches off until the particle swings halfway around; the field
+then becomes negative in front of the particle again, and again attracts
+it. As the particle moves faster and faster it spirals outward in an
+ever increasing circle, something like a tether ball unwinding from a
+pole. The energies achieved would have seemed fantastic to earlier
+scientists. The Bevatron, a modern offspring of the first cyclotron,
+accelerates protons to 99.13% the speed of light, thereby giving them
+6.2 billion electron volts (BeV).
+
+Another instrument, the heavy-ion linear accelerator (Hilac),
+accelerates ions as heavy as neon to about 15% the speed of light. It is
+called a linear accelerator because it accelerates particles in a
+straight line. Stanford University is currently (1963) in the process of
+building a linear accelerator approximately two miles long which will
+accelerate charged particles to 99.9% the speed of light.
+
+But highly accelerated charged particles did not solve all of science's
+questions about the inner workings of the nucleus.
+
+In 1932, during the early search for more efficient ways to bombard
+nuclei, James Chadwick discovered the neutron. This particle, which is
+neutral in charge and is approximately the same mass as a proton, has
+the remarkable quality of efficiently producing nuclear reactions even
+at very low energies. No one exactly knowns why. At low energies,
+protons, alpha particles, or other charged particles do not interact
+with nuclei because they cannot penetrate the electrostatic energy
+barriers. For example, slow positive particles pick up electrons, become
+neutral, and lose their ability to cause nuclear transformations. Slow
+neutrons, on the other hand, can enter nearly all atomic nuclei and
+induce fission of certain of the heavier ones. It is, in fact, these
+properties of the neutron which have made possible the utilization of
+atomic energy.
+
+With these tools, researchers were not long in accurately identifying
+the missing elements 43, 61, 85, and 87 and more--indeed, the list of
+new elements, isotopes, and particles now seems endless.
+
+Element 43 was "made" for the first time as a result of bombarding
+molybdenum with deuterons in the Berkeley cyclotron. The chemical work
+of identifying the element was done by Emilio Segrč and others then
+working at Palermo, Sicily, and they chose to call it technetium,
+because it was the element first made by artificial technical methods.
+
+Element 61 was made for the first time from the fission disintegration
+products of uranium in the Clinton (Oak Ridge) reactor. Marinsky and
+Glendenin, who did the chemical work of identification, chose to call it
+promethium because they wished to point out that just as Prometheus
+stole fire (a great force for good or evil) from the hidden storehouse
+of the gods and presented it to man, so their newly assembled reactor
+delivered to mankind an even greater force, nuclear energy.
+
+Element 85 is called astatine, from the Greek astatos, meaning
+"unstable," because astatine _is_ unstable (of course all other elements
+having a nuclear charge number greater than 84 are unstable, too).
+Astatine was first made at Berkeley by bombarding bismuth with alpha
+particles, which produced astatine and released two neutrons. The
+element has since been found in nature as a small constituent of the
+natural decay of actinium.
+
+The last of the original 92 elements to be discovered was element 87,
+francium. It was identified in 1939 by French scientist Marguerite
+Perey.
+
+Children have a game in which they pile blocks up to see how high they
+can go before they topple over. In medieval times, petty rulers in their
+Italian states vied with one another to see who could build the tallest
+tower. Some beautiful results of this game still remain in Florence,
+Siena, and other Italian hill cities. Currently, Americans vie in a
+similar way with the wheelbase and overall length of their cars. After
+1934, the game among scientists took the form of seeing who could extend
+the length of the periodic system of the elements; as with medieval
+towers, it was Italy that again began with the most enthusiasm and
+activity under the leadership of Enrico Fermi.
+
+Merely adding neutrons would not be enough; that would make only a
+heavier isotope of the already known heaviest elements, uranium.
+However, if the incoming neutron caused some rearrangement within the
+nucleus and if it were accompanied by expulsion of electrons, that
+_would_ make a new element. Trials by Fermi and his co-workers with
+various elements led to unmistakeable evidence of the expulsion of
+electrons (beta activity) with at least four different rates of decay
+(half-lives). Claims were advanced for the creation of elements 93 and
+94 and possibly further (the transuranium elements, Table I). Much
+difficulty was experienced, however, in proving that the activity really
+was due to the formation of elements 93 and 94. As more people became
+interested and extended the scope of the experiments, the picture became
+more confused rather than clarified. Careful studies soon showed that
+the activities did _not_ decay logarithmically--which means that they
+were caused by mixtures, not individual pure substances--and the
+original four activities reported by Fermi grew to at least nine.
+
+As a matter of fact, the way out of the difficulty had been indicated
+soon after Fermi's original announcement. Dr. Ida Noddack pointed out
+that no one had searched among the products of Fermi's experiment for
+elements _lighter_ than lead, but no one paid any attention to her
+suggestion at the time. The matter was finally cleared up by Dr. Otto
+Hahn and F. Strassmann. They were able to show that instead of uranium
+having small pieces like helium nuclei, fast electrons, and super-hard
+x-rays, knocked off as expected, the atom had split into two roughly
+equal pieces, together with some excess neutrons. This process is called
+nuclear fission. The two large pieces were unstable and decayed further
+with the loss of electrons, hence the [beta] activity. This process is
+so complicated that there are not, as originally reported, only four
+half-lives, but at least 200 different varieties of at least 35
+different elements. The discovery of fission attended by the release of
+enormous amounts of energy led to feverish activity on the part of
+physicists and chemists everywhere in the world. In June 1940, McMillan
+and Abelson presented definite proof that element 93 had been found in
+uranium penetrated by neutrons during deuteron bombardment in the
+cyclotron at the University of California Radiation Laboratory.
+
+The California scientists called the newly discovered element neptunium,
+because it lies beyond the element uranium just as the planet Neptune
+lies beyond Uranus. The particular isotope formed in those first
+experiments was {93}Np<239>; this is read neptunium having a nuclear charge
+of 93 and an atomic mass number of 239. It has a half-life of 2.3 days,
+during which it gives up another electron ([beta] particle) and becomes
+element 94, or plutonium (so called after Pluto, the next planet beyond
+Neptune). This particular form of plutonium ({94}Pu<239>) has such a long
+half-life (24,000 years) that it could not be detected. The first
+isotope of element 94 to be discovered was Pu<238>, made by direct deuteron
+bombardment in the Berkeley 60-inch cyclotron by Radiation Laboratory
+scientists Seaborg, McMillan, Kennedy, and Wahl; it had an [alpha]-decay
+half-life of 86.4 years, which gave it sufficient radioactivity so that
+its chemistry could be studied.
+
+Having found these chemical properties in Pu<238>, experimenters knew
+{94}Pu<239> would behave similarly. It was soon shown that the nucleus of
+{94}Pu<239> would undergo fission in the same way as {92}U<235> when
+bombarded with slow neutrons and that it could be produced in the newly
+assembled atomic pile. Researchers wished to learn as much as possible
+about its chemistry; therefore, during the summer of 1942 two large
+cyclotrons at St. Louis and Berkeley bombarded hundreds of pounds of
+uranium almost continuously. This resulted in the formation of 200
+micrograms of plutonium. From this small amount, enough of the chemical
+properties of the element were learned to permit correct design of the
+huge plutonium-recovery plant at Hanford, Washington. In the course of
+these investigations, balances that would weigh up to 10.5 mg with a
+sensitivity of 0.02 microgram were developed. The "test tubes" and
+"beakers" used had internal diameters of 0.1 to 1 mm and could measure
+volumes of 1/10 to 1/10,000 ml with an accuracy of 1%. The fact that
+there was no intermediate stage of experimentation, but a direct
+scale-up at Hanford of ten billion times, required truly heroic skill
+and courage.
+
+By 1944 sufficient plutonium was available from uranium piles (reactors)
+so that it was available as target material for cyclotrons. At Berkeley
+it was bombarded with 32-MeV doubly charged helium ions, and the
+following reactions took place:
+
+    {94}Pu<239> ([alpha], n) {96}Cm<242> [alpha] / 150 days --> {94}Pu<238>.
+
+This is to be read: plutonium having an atomic number of 94 (94
+positively charged protons in the nucleus) and a mass number of 239 (the
+whole atom weighs approximately 239 times as much as a proton), when
+bombarded with alpha particles (positively charged helium nuclei) reacts
+to give off a neutron and a new element, curium, that has atomic number
+96 and mass number 242. This gives off alpha particles at such a rate
+that half of it has decomposed in 150 days, leaving plutonium with
+atomic number 94 and mass number 238. The radiochemical work leading to
+the isolation and identification of the atoms of element 96 was done at
+the metallurgical laboratory of the University of Chicago.
+
+The intense neutron flux available in modern reactors led to a new
+element, americium (Am), as follows:
+
+    {94}Pu<239> (n, [gamma]) {94}Pu<240> (n, [gamma]) {94}Pu<241> [beta]
+            --> {95}Am<241>.
+
+The notation (n, [gamma]) means that the plutonium absorbs a neutron and
+gives off some energy in the form of gamma rays (very hard x rays); it
+first forms {94}Pu<240> and then {94}Pu<241>, which is unstable and gives
+off fast electrons ([beta]), leaving {95}Am<241>.
+
+Berkelium and californium, elements 97 and 98, were produced at the
+University of California by methods analogous to that used for curium,
+as shown in the following equations:
+
+    {95}Am<240> + [alpha] --> {97}Bk<243> + {0}n<1>,
+
+and {96}Cm<241> + [alpha] --> {98}Cf<244> + {0}n<1>.
+
+The next two elements, einsteinium ({99}Es) and fermium ({100}Fm), were
+originally found in the debris from the thermonuclear device "Mike,"
+which was detonated on Eniwetok atoll November 1952. (This method of
+creating new substances is somewhat more extravagant than the mythical
+Chinese method of burning down a building to get a roast pig.)
+
+These elements have since been made in nuclear reactors and by
+bombardment. This time the "bullet" was N<14> stripped of electrons till it
+had a charge of +6, and the target was plutonium.
+
+Researchers at the University of California used new techniques in
+forming and identifying element 101, mendelevium. A very thin layer of
+{99}Es<253> was electroplated onto a thin gold foil and was then bombarded,
+from behind the layer, with 41-MeV [alpha] particles. Unchanged {99}Es<253>
+stayed on the gold, but those atoms hit by [alpha] particles were
+knocked off and deposited on a "catcher" gold foil, which was then
+dissolved and analyzed (Fig. 3). This freed the new element from most of
+the very reactive parent substances, so that analysis was easier. Even
+so, the radioactivity was so weak that the new element was identified
+"one atom at a time"; this is possible because its daughter element,
+fermium, spontaneously fissions and releases energy in greater bursts
+than any possible contaminant.
+
+[Illustration: Fig. 3. The production of mendelevium.]
+
+In 1957, in Stockholm, element 102 was reported found by an
+international team of scientists (who called it nobelium), but diligent
+and extensive research failed to duplicate the Stockholm findings.
+However, a still newer technique developed at Berkeley showed the
+footprints--if not the living presence--of 102 (see Fig. 4). The rare
+isotope curium-246 is coated on a small piece of nickel foil, enclosed
+in a helium-filled container, and placed in the heavy-ion linear
+accelerator (Hilac) beam. Positively charged atoms of element 102 are
+knocked off the foil by the beam, which is of carbon-12 or carbon-13
+nuclei, and are deposited on a negatively charged conveyor apron. But
+element 102 doesn't live long enough to be actually measured. As it
+decays, its daughter product, {100}Fm<250>, is attracted onto a charged
+aluminum foil where it can be analyzed. The researchers have decided
+that the hen really did come first: they have the egg; therefore the hen
+must have existed. By measuring the time distance between target and
+daughter product, they figure that the hen-mother (element 102) must
+have a half-life of three seconds.
+
+[Illustration: Fig. 4. The experimental arrangement used in the
+discovery of element 102.]
+
+In an experiment completed in 1961, researchers at the University of
+California at Berkeley unearthed similar "footprints" belonging to
+element 103 (named lawrencium in honor of Nobel prizewinner Ernest O.
+Lawrence). They found that the bombardment of californium with boron
+ions released [alpha] particles which had an energy of 8.6 MeV and
+decayed with a half-life of 8 ± 2 seconds. These particles can only be
+produced by element 103, which, according to one scientific theory, is a
+type of "dinosaur" of matter that died out a few weeks after creation of
+the universe.
+
+The half-life of lawrencium (Lw) is about 8 seconds, and its mass number
+is thought to be 257, although further research is required to establish
+this conclusively.
+
+Research on lawrencium is complicated. Its total [alpha] activity
+amounts to barely a few counts per hour. And, since scientists had the
+[alpha]-particle "footprints" only and not the beast itself, the
+complications increased. Therefore no direct chemical techniques could
+be used, and element 103 was the first to be discovered solely by
+nuclear methods.[A]
+
+For many years the periodic system was considered closed at 92. It has
+now been extended by at least eleven places (Table I), and one of the
+extensions (plutonium) has been made in truckload lots. Its production
+and use affect the life of everyone in the United States and most of the
+world.
+
+Surely the end is again in sight, at least for ordinary matter, although
+persistent scientists may shift their search to the other-world "anti"
+particles. These, too, will call for very special techniques for
+detection of their fleeting presence.
+
+Early enthusiastic researchers complained that a man's life was not long
+enough to let him do all the work he would like on an element. The
+situation has now reached a state of equilibrium; neither man nor
+element lives long enough to permit all the desired work.
+
+[A] In August 1964 Russian scientists claimed that they created element
+104 with a half-life of about 0.3 seconds by bombarding plutomium with
+accelerated neon-22 ions.
+
+
+Table I. THE TRANSURANIUM ELEMENTS
+
+  ========================================================================
+  Element    Name (Symbol)     Mass     Year Discovered; by whom;
+                              Number          where; how
+  ------------------------------------------------------------------------
+     93     Neptunium (Np)      238    1940; E. M. McMillan, P. H.
+                                       Abelson; University of California
+                                       at Berkeley; slow-neutron
+                                       bombardment of U<238> in the
+                                       60-inch cyclotron.
+  ------------------------------------------------------------------------
+     94     Plutonium (Pu)      238    1941; J. W. Kennedy, E. M.
+                                       McMillan, G. T. Seaborg, and A. C.
+                                       Wahl; University of California at
+                                       Berkeley; 16-MeV deuteron
+                                       bombardment of U<238> in the
+                                       60-inch cyclotron.
+
+                      (Pu)      239    Pu<239>; the fissionable isotope
+                                       of plutonium, was also discovered
+                                       in 1941 by J. W. Kennedy, G. T.
+                                       Seaborg, E. Segrč and A. C. Wahl;
+                                       University of California at
+                                       Berkeley; slow-neutron bombardment
+                                       of U<238> in the 60-inch
+                                       cyclotron.
+  ------------------------------------------------------------------------
+     95     Americium (Am)      241    1944-45; Berkeley scientists A.
+                                       Ghiorso, R. A. James, L. O.
+                                       Morgan, and G. T. Seaborg at the
+                                       University of Chicago; intense
+                                       neutron bombardment of plutonium
+                                       in nuclear reactors.
+  ------------------------------------------------------------------------
+     96     Curium (Cm)         242    1945; Berkeley scientists A.
+                                       Ghiorso, R. A. James, and G. T.
+                                       Seaborg at the University of
+                                       Chicago; bombardment of Pu<239>
+                                       by 32-MeV helium ions from the
+                                       60-inch cyclotron.
+  ------------------------------------------------------------------------
+     97     Berkelium (Bk)      243    1949; S. G. Thompson, A. Ghiorso,
+                                       and G. T. Seaborg; University of
+                                       California at Berkeley; 35-MeV
+                                       helium-ion bombardment of
+                                       Am<241>.
+  ------------------------------------------------------------------------
+     98     Californium (Cf)    245    1950; S. G. Thompson, K. Street,
+                                       A. Ghiorso, G. T. Seaborg;
+                                       University of California at
+                                       Berkeley; 35-MeV helium-ion
+                                       bombardment of Cm<242>.
+  ------------------------------------------------------------------------
+     99     Einsteinium (Es)    253    1952-53; A. Ghiorso, S. G.
+    100     Fermium (Fm)        255    Thompson, G. H. Higgins, G. T.
+                                       Seaborg, M. H. Studier, P. R.
+                                       Fields, S. M. Fried, H. Diamond,
+                                       J. F. Mech, G. L. Pyle, J. R.
+                                       Huizenga, A. Hirsch, W. M.
+                                       Manning, C. I. Browne, H. L.
+                                       Smith, R. W. Spence; "Mike"
+                                       explosion in South Pacific; work
+                                       done at University of California
+                                       at Berkeley, Los Alamos Scientific
+                                       Laboratory, and Argonne National
+                                       Laboratory; both elements created
+                                       by multiple capture of neutrons in
+                                       uranium of first detonation of a
+                                       thermonuclear device. The elements
+                                       were chemically isolated from the
+                                       debris of the explosion.
+  ------------------------------------------------------------------------
+    101     Mendelevium (Md)    256    1955; A. Ghiorso, B. G. Harvey, G.
+                                       R. Choppin, S. G. Thompson, G. T.
+                                       Seaborg; University of California
+                                       at Berkeley; 41-MeV helium-ion
+                                       bombardment of Es<253> in 60-inch
+                                       cyclotron.
+  ------------------------------------------------------------------------
+    102     Unnamed[B]          254    1958; A. Ghiorso, T. Sikkeland, A.
+                                       E. Larsh, R. M. Latimer;
+                                       University of California, Lawrence
+                                       Radiation Laboratory, Berkeley;
+                                       68-MeV carbon-ion bombardment of
+                                       Cm<246> in heavy-ion linear
+                                       accelerator (Hilac).
+  ------------------------------------------------------------------------
+    103     Lawrencium          257    1961; A. Ghiorso, T. Sikkeland, A.
+                                       E. Larsh, R. M. Latimer;
+                                       University of California, Lawrence
+                                       Radiation Laboratory, Berkeley;
+                                       70-MeV boron-ion bombardment of
+                                       Cf<250>, Cf<251>, and Cf<252>
+                                       in Hilac.
+  ========================================================================
+
+[B] A 1957 claim for the synthesis and identification of element 102 was
+accepted at that time by the International Union of Pure and Applied
+Chemistry, and the name nobelium (symbol No) was adopted. The University
+of California scientists, A. Ghiorso et al., cited here believe they
+have disproved the earlier claim and have the right to suggest a
+different name for the element.
+
+
+
+
+
+End of the Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
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+<pre>
+
+The Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: A Brief History of Element Discovery, Synthesis, and Analysis
+
+Author: Glen W. Watson
+
+Release Date: March 13, 2010 [EBook #31624]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELEMENT DISCOVERY ***
+
+
+
+
+Produced by Mark C. Orton, Erica Pfister-Altschul and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+</pre>
+
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/bcover.png" width="383" height="600" alt="Back Cover: A Brief History of Element Discovery, Synthesis, and Analysis" title="" />
+<img src="images/fcover.png" width="383" height="600" alt="Front Cover: A Brief History of Element Discovery, Synthesis, and Analysis" title="" />
+</div>
+
+<h1>A Brief History<br />
+of<br />
+ELEMENT DISCOVERY,<br />
+SYNTHESIS, and ANALYSIS</h1>
+
+
+<h3>Glen W. Watson</h3>
+<h4>September 1963</h4>
+
+<div class="figcenter" style="width: 100px;">
+<img src="images/logo.png" width="100" height="190" alt="Lawrence Radiation Laboratory logo" title="" />
+</div>
+
+<h3>LAWRENCE RADIATION LABORATORY<br />
+University of California<br />
+Berkeley and Livermore</h3>
+
+
+<h4>Operating under contract with the<br />
+United States Atomic Energy Commission</h4>
+
+<div class="figcenter" style="width: 400px;">
+<a href="images/fig0_800.png"><img src="images/fig0_400.png" width="400" height="544" alt="Radioactive elements: alpha particles from a speck of radium
+leave tracks on a photographic emulsion. (Occhialini and Powell, 1947)" title="" /></a>
+<span class="caption">Radioactive elements: alpha particles from a speck of radium
+leave tracks on a photographic emulsion. (Occhialini and Powell, 1947)</span>
+</div>
+
+
+
+<hr style="width: 65%;" />
+<div><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></div>
+<h2>A BRIEF HISTORY OF<br />
+ELEMENT DISCOVERY, SYNTHESIS,<br />
+AND ANALYSIS</h2>
+
+
+<p>It is well known that the number of elements has grown from
+four in the days of the Greeks to 103 at present, but the change in
+methods needed for their discovery is not so well known. Up until
+1939, only 88 naturally occurring elements had been discovered.
+It took a dramatic modern technique (based on Ernest O. Lawrence's
+Nobel-prize-winning atom smasher, the cyclotron) to synthesize
+the most recently discovered elements. Most of these
+recent discoveries are directly attributed to scientists working under
+the Atomic Energy Commission at the University of California's
+Radiation Laboratory at Berkeley.</p>
+
+<p>But it is apparent that our present knowledge of the elements
+stretches back into history: back to England's Ernest Rutherford,
+who in 1919 proved that, occasionally, when an alpha particle
+from radium strikes a nitrogen atom, either a proton or a hydrogen
+nucleus is ejected; to the Dane Niels Bohr and his 1913 idea
+of electron orbits; to a once unknown Swiss patent clerk, Albert
+Einstein, and his now famous theories; to Poland's Marie Curie
+who, in 1898, with her French husband Pierre laboriously isolated
+polonium and radium; back to the French scientist H. A. Becquerel,
+who first discovered something he called a "spontaneous
+emission of penetrating rays from certain salts of uranium"; to
+the German physicist W. K. Roentgen and his discovery of x rays
+in 1895; and back still further.</p>
+
+<p>During this passage of scientific history, the very idea of
+"element" has undergone several great changes.</p>
+
+<div><span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span></div><p>The early Greeks suggested earth, air, fire, and water as being
+the essential material from which all others were made. Aristotle
+considered these as being combinations of four properties: hot,
+cold, dry, and moist (see Fig. 1).</p>
+
+<div class="figcenter" style="width: 600px;">
+<a href="images/fig1_1200.png"><img src="images/fig1_600.png" width="600" height="562" alt="Fig. 1. The elements as proposed by the early Greeks." title="" /></a>
+<span class="caption">Fig. 1. The elements as proposed by the early Greeks.</span>
+</div>
+
+<p>Later, a fifth "essence," ether, the building material of the
+heavenly bodies was added.</p>
+
+<p>Paracelsus (1493-1541) introduced the three alchemical symbols
+salt, sulfur, and mercury. Sulfur was the principle of combustability,
+salt the fixed part left after burning (calcination), and
+mercury the essential part of all metals. For example, gold and
+silver were supposedly different combinations of sulfur and
+mercury.</p>
+
+<div><span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span></div><p>Robert Boyle in his "Sceptical Chymist" (1661) first defined
+the word element in the sense which it retained until the discovery
+of radioactivity (1896), namely, a form of matter that could not be
+split into simpler forms.</p>
+
+<p>The first discovery of a true element in historical time was
+that of phosphorus by Dr. Brand of Hamburg, in 1669. Brand
+kept his process secret, but, as in modern times, knowledge of
+the element's existence was sufficient to let others, like Kunkel
+and Boyle in England, succeed independently in isolating it
+shortly afterward.</p>
+
+<p>As in our atomic age, a delicate balance was made between
+the "light-giving" (desirable) and "heat-giving" (feared) powers
+of a discovery. An early experimenter was at first "delighted with
+the white, waxy substance that glowed so charmingly in the dark
+of his laboratory," but later wrote, "I am not making it any
+more for much harm may come of it."</p>
+
+<p>Robert Boyle wrote in 1680 of phosphorus, "It shone so
+briskly and lookt so oddly that the sight was extreamly pleasing,
+having in it a mixture of strangeness, beauty and frightfulness."</p>
+
+<p>These words describe almost exactly the impressions of eye
+witnesses of the first atom bomb test at Alamagordo, New Mexico,
+July 16, 1945.</p>
+
+<p>For the next two and three-quarters centuries the chemists
+had much fun and some fame discovering new elements. Frequently
+there was a long interval between discovery and recognition.
+Thus Scheele made chlorine in 1774 by the action of "black
+manganese" (manganese dioxide) on concentrated muriatic acid
+(hydrochloric acid), but it was not recognized as an element till
+the work of Davy in 1810.</p>
+
+<p>Occasionally the development of a new technique would lead
+to the "easy" discovery of a whole group of new elements. Thus
+Davy, starting in 1807, applied the method of electrolysis, using
+a development of Volta's pile as a source of current; in a short
+time he discovered aluminum, barium, boron, calcium, magnesium,
+potassium, sodium, and strontium.</p>
+
+<div><span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span></div><p>The invention of the spectroscope by Bunsen and Kirchhoff
+in 1859 provided a new tool which could establish the purity of
+substances already known and lead to the discovery of others.
+Thus, helium was discovered in the sun's spectrum by Jansen and
+isolated from uranite by Ramsay in 1895.</p>
+
+<p>The discovery of radioactivity by Becquerel in 1896 (touched
+off by Roentgen's discovery of x rays the year before) gave an
+even more sensitive method of detecting the presence or absence
+of certain kinds of matter. It is well known that Pierre and Marie
+Curie used this new-found radioactivity to identify the new
+elements polonium and radium. Compounds of these new elements
+were obtained by patient fractional recrystallization of their salts.</p>
+
+<p>The "explanation" of radioactivity led to the discovery of
+isotopes by Rutherford and Soddy in 1914, and with this discovery
+a revision of our idea of elements became necessary. Since Boyle,
+it had been assumed that all atoms of the individual elements
+were identical and unlike any others, and could not be changed
+into anything simpler. Now it became evident that the atoms of
+radioactive elements were constantly changing into other elements,
+thereby releasing very large amounts of energy, and that
+many different forms of the same element (lead was the first
+studied) were possible. We now think of an element as a form of
+matter in which all atoms have the same nuclear charge.</p>
+
+<p>The human mind has always sought order and simplification
+of the external world; in chemistry the fruitful classifications
+were Dobereiner's Triads (1829), Newland's law of octaves (1865),
+and Mendeleev's periodic law (1869). The chart expressing this
+periodic law seemed to indicate the maximum extent of the elements
+and gave good hints "where to look for" and "the probable
+properties of" the remaining ones (see Fig. 2).</p>
+
+<p>By 1925, all but four of the slots in the 92-place file had been
+filled. The vacancies were at 43, 61, 85, and 87.</p>
+
+<div><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span></div>
+<div class="figcenter" style="width: 600px;">
+<a href="images/fig2_1200.png"><img src="images/fig2_600.png" width="600" height="312" alt="Fig. 2. Periodic chart of the elements (1963)" title="" /></a>
+<span class="caption">Fig. 2. Periodic chart of the elements (1963)</span>
+</div>
+
+<p>Workers using traditional analytical techniques continued to
+search for these elements, but their efforts were foredoomed to
+failure. None of the nuclei of the isotopes of elements 43, 61, 85,<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span>
+and 87 are stable; hence weighable quantities of them do not exist
+in nature, and new techniques had to be developed before we
+could really say we had "discovered" them.</p>
+
+<p>In 1919, Rutherford accomplished scientifically what medieval
+alchemists had failed to do with "magic" experiments and
+other less sophisticated techniques. It wasn't gold (the goal of
+the alchemists) he found but something more valuable with even
+greater potential for good and evil: a method of transmuting one
+element into another. By bombarding nitrogen nuclei with alpha
+particles from radium, he found that nitrogen was changed into
+oxygen.</p>
+
+<p>The process for radioactive transmutation is somewhat like
+a common chemical reaction. An alpha particle, which has the
+same charge (+2) and atomic mass (4) as a helium nucleus, penetrates
+the repulsive forces of the nitrogen nucleus and deposits
+one proton and one neutron; this changes the nitrogen atom into
+an oxygen atom. The reaction is written</p>
+
+<div class="figcenter">
+<a name="Eqn_1" id="Eqn_1"><img src="images/eqn1.png" width="269" height="23" alt="[7]N[14] + [2]He[4] &rarr; [1]H[1] + [8]O[17]" title="[7]N[14] + [2]He[4] &rarr; [1]H[1] + [8]O[17]" /></a>
+</div>
+
+<p>The number at the lower left of each element symbol in the
+above reaction is the proton number. This number determines
+the basic chemical identity of an atom, and it is this number
+scientists must change before one element can be transformed into
+another. The common way to accomplish this artificially is by
+bombarding nuclei with nuclear projectiles.</p>
+
+<p>Rutherford used naturally occurring alpha particles from
+radium as his projectiles because they were the most effective he
+could then find. But these natural alpha particles have several
+drawbacks: they are positively charged, like the nucleus itself,
+and are therefore more or less repulsed depending on the proton
+number of the element being bombarded; they do not move fast
+enough to penetrate the nuclei of heavier elements (those with
+many protons); and, for various other reasons (some of them
+unexplained), are inefficient in breaking up the nucleus. It is
+estimated that only 1 out of 300,000 of these alpha particles will
+react with nitrogen.</p>
+
+<div><span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></div>
+<p>Physicists immediately began the search for artificial means
+to accelerate a wider variety of nuclear particles to high energies.</p>
+
+<p>Protons, because they have a +1 charge rather than the +2
+charge of the alpha particles, are repulsed less strongly by the
+positive charge on the nucleus, and are therefore more useful as
+bombarding projectiles. In 1929, E. T. S. Walton and J. D. Cockcroft
+passed an electric discharge through hydrogen gas, thereby
+removing electrons from the hydrogen atom; this left a beam
+of protons (i. e., hydrogen ions), which was then accelerated by
+high voltages. This Cockcroft-Walton voltage multiplier accelerated
+the protons to fairly high energies (about 800,000 electron
+volts), but the protons still had a plus charge and their energies
+were still not high enough to overcome the repulsive forces
+(Coulombic repulsion) of the heavier nuclei.</p>
+
+<p>A later development, the Van de Graaff electrostatic generator,
+produced a beam of hydrogen ions and other positively
+charged ions, and electrons at even higher energies. An early
+model of the linear accelerator also gave a beam of heavy positive
+ions at high energies. These were the next two instruments devised
+in the search for efficient bombarding projectiles. However, the
+impasse continued: neither instrument allowed scientists to crack
+the nuclei of the heavier elements.</p>
+
+<p>Ernest O. Lawrence's cyclotron, built in 1931, was the first
+device capable of accelerating positive ions to the very high
+energies needed. Its basic principle of operation is not difficult
+to understand. A charged particle accelerated in a cyclotron is
+analogous to a ball being whirled on a string fastened to the top of
+a pole. A negative electric field attracts the positively charged
+particle (ball) towards it and then switches off until the particle
+swings halfway around; the field then becomes negative in front
+of the particle again, and again attracts it. As the particle moves
+faster and faster it spirals outward in an ever increasing circle,
+something like a tether ball unwinding from a pole. The energies
+achieved would have seemed fantastic to earlier scientists. The
+Bevatron, a modern offspring of the first cyclotron, accelerates
+protons to 99.13% the speed of light, thereby giving them 6.2
+billion electron volts (BeV).</p>
+
+<div><span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span></div><p>Another instrument, the heavy-ion linear accelerator (Hilac),
+accelerates ions as heavy as neon to about 15% the speed of
+light. It is called a linear accelerator because it accelerates particles
+in a straight line. Stanford University is currently (1963) in
+the process of building a linear accelerator approximately two
+miles long which will accelerate charged particles to 99.9% the
+speed of light.</p>
+
+<p>But highly accelerated charged particles did not solve all of
+science's questions about the inner workings of the nucleus.</p>
+
+<p>In 1932, during the early search for more efficient ways to
+bombard nuclei, James Chadwick discovered the neutron. This
+particle, which is neutral in charge and is approximately the same
+mass as a proton, has the remarkable quality of efficiently producing
+nuclear reactions even at very low energies. No one exactly
+knowns why. At low energies, protons, alpha particles, or other
+charged particles do not interact with nuclei because they cannot
+penetrate the electrostatic energy barriers. For example, slow
+positive particles pick up electrons, become neutral, and lose
+their ability to cause nuclear transformations. Slow neutrons, on
+the other hand, can enter nearly all atomic nuclei and induce
+fission of certain of the heavier ones. It is, in fact, these properties
+of the neutron which have made possible the utilization of atomic
+energy.</p>
+
+<p>With these tools, researchers were not long in accurately
+identifying the missing elements 43, 61, 85, and 87 and more&mdash;indeed,
+the list of new elements, isotopes, and particles now
+seems endless.</p>
+
+<p>Element 43 was "made" for the first time as a result of
+bombarding molybdenum with deuterons in the Berkeley cyclotron.
+The chemical work of identifying the element was done by
+Emilio Segr&egrave; and others then working at Palermo, Sicily, and
+they chose to call it technetium, because it was the element first
+made by artificial technical methods.</p>
+
+<p>Element 61 was made for the first time from the fission disintegration
+products of uranium in the Clinton (Oak Ridge)<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span>
+reactor. Marinsky and Glendenin, who did the chemical work of
+identification, chose to call it promethium because they wished to
+point out that just as Prometheus stole fire (a great force for good
+or evil) from the hidden storehouse of the gods and presented it to
+man, so their newly assembled reactor delivered to mankind an
+even greater force, nuclear energy.</p>
+
+<p>Element 85 is called astatine, from the Greek astatos, meaning
+"unstable," because astatine <i>is</i> unstable (of course all other
+elements having a nuclear charge number greater than 84 are
+unstable, too). Astatine was first made at Berkeley by bombarding
+bismuth with alpha particles, which produced astatine and released
+two neutrons. The element has since been found in nature as a
+small constituent of the natural decay of actinium.</p>
+
+<p>The last of the original 92 elements to be discovered was
+element 87, francium. It was identified in 1939 by French scientist
+Marguerite Perey.</p>
+
+<p>Children have a game in which they pile blocks up to see
+how high they can go before they topple over. In medieval times,
+petty rulers in their Italian states vied with one another to see who
+could build the tallest tower. Some beautiful results of this game
+still remain in Florence, Siena, and other Italian hill cities. Currently,
+Americans vie in a similar way with the wheelbase and
+overall length of their cars. After 1934, the game among scientists
+took the form of seeing who could extend the length of the
+periodic system of the elements; as with medieval towers, it was
+Italy that again began with the most enthusiasm and activity
+under the leadership of Enrico Fermi.</p>
+
+<p>Merely adding neutrons would not be enough; that would
+make only a heavier isotope of the already known heaviest elements,
+uranium. However, if the incoming neutron caused some
+rearrangement within the nucleus and if it were accompanied by
+expulsion of electrons, that <i>would</i> make a new element. Trials by
+Fermi and his co-workers with various elements led to unmistakeable
+evidence of the expulsion of electrons (beta activity) with at
+least four different rates of decay (half-lives). Claims were advanced<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span>
+for the creation of elements 93 and 94 and possibly further (the
+transuranium elements, Table I). Much difficulty was experienced,
+however, in proving that the activity really was due to the formation
+of elements 93 and 94. As more people became interested
+and extended the scope of the experiments, the picture became
+more confused rather than clarified. Careful studies soon showed
+that the activities did <i>not</i> decay logarithmically&mdash;which means
+that they were caused by mixtures, not individual pure substances&mdash;and
+the original four activities reported by Fermi grew
+to at least nine.</p>
+
+<p>As a matter of fact, the way out of the difficulty had been
+indicated soon after Fermi's original announcement. Dr. Ida
+Noddack pointed out that no one had searched among the products
+of Fermi's experiment for elements <i>lighter</i> than lead, but no one
+paid any attention to her suggestion at the time. The matter was
+finally cleared up by Dr. Otto Hahn and F. Strassmann. They
+were able to show that instead of uranium having small pieces like
+helium nuclei, fast electrons, and super-hard x-rays, knocked off
+as expected, the atom had split into two roughly equal pieces,
+together with some excess neutrons. This process is called nuclear
+fission. The two large pieces were unstable and decayed further
+with the loss of electrons, hence the &beta; activity. This process is so
+complicated that there are not, as originally reported, only four
+half-lives, but at least 200 different varieties of at least 35 different
+elements. The discovery of fission attended by the release of
+enormous amounts of energy led to feverish activity on the part
+of physicists and chemists everywhere in the world. In June 1940,
+McMillan and Abelson presented definite proof that element 93
+had been found in uranium penetrated by neutrons during deuteron
+bombardment in the cyclotron at the University of California
+Radiation Laboratory.</p>
+
+<p>The California scientists called the newly discovered element
+neptunium, because it lies beyond the element uranium just as
+the planet Neptune lies beyond Uranus. The particular isotope
+formed in those first experiments was <sub>93</sub>Np<sup>239</sup>; this is read neptunium
+having a nuclear charge of 93 and an atomic mass number<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span>
+of 239. It has a half-life of 2.3 days, during which it gives up
+another electron (&beta; particle) and becomes element 94, or plutonium
+(so called after Pluto, the next planet beyond Neptune). This
+particular form of plutonium (<sub>94</sub>Pu<sup>239</sup>) has such a long half-life
+(24,000 years) that it could not be detected. The first isotope of
+element 94 to be discovered was Pu<sup>238</sup>, made by direct deuteron
+bombardment in the Berkeley 60-inch cyclotron by Radiation
+Laboratory scientists Seaborg, McMillan, Kennedy, and Wahl; it
+had an &alpha;-decay half-life of 86.4 years, which gave it sufficient
+radioactivity so that its chemistry could be studied.</p>
+
+<p>Having found these chemical properties in Pu<sup>238</sup>, experimenters
+knew <sub>94</sub>Pu<sup>239</sup> would behave similarly. It was soon shown
+that the nucleus of <sub>94</sub>Pu<sup>239</sup> would undergo fission in the same way
+as <sub>92</sub>U<sup>235</sup> when bombarded with slow neutrons and that it could
+be produced in the newly assembled atomic pile. Researchers
+wished to learn as much as possible about its chemistry; therefore,
+during the summer of 1942 two large cyclotrons at St. Louis and
+Berkeley bombarded hundreds of pounds of uranium almost continuously.
+This resulted in the formation of 200 micrograms of
+plutonium. From this small amount, enough of the chemical
+properties of the element were learned to permit correct design of
+the huge plutonium-recovery plant at Hanford, Washington. In
+the course of these investigations, balances that would weigh up
+to 10.5 mg with a sensitivity of 0.02 microgram were developed.
+The "test tubes" and "beakers" used had internal diameters of
+0.1 to 1 mm and could measure volumes of 1/10 to 1/10,000 ml
+with an accuracy of 1%. The fact that there was no intermediate
+stage of experimentation, but a direct scale-up at Hanford of ten
+billion times, required truly heroic skill and courage.</p>
+
+<p>By 1944 sufficient plutonium was available from uranium
+piles (reactors) so that it was available as target material for
+cyclotrons. At Berkeley it was bombarded with 32-MeV doubly
+charged helium ions, and the following reactions took place:</p>
+
+<div class="figcenter">
+<a name="Eqn_2" id="Eqn_2"><img src="images/eqn2.png" width="379" height="42" alt="[94]Pu[239] (&alpha;, n) [96]Cm[242] &alpha;/150 days &rarr; [94]Pu[238]" title="[94]Pu[239] (&alpha;, n) [96]Cm[242] &alpha;/150 days &rarr; [94]Pu[238]" /></a>
+</div>
+
+<div><span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span></div><p>This is to be read: plutonium having an atomic number of 94 (94
+positively charged protons in the nucleus) and a mass number of
+239 (the whole atom weighs approximately 239 times as much as
+a proton), when bombarded with alpha particles (positively
+charged helium nuclei) reacts to give off a neutron and a new element,
+curium, that has atomic number 96 and mass number 242.
+This gives off alpha particles at such a rate that half of it has
+decomposed in 150 days, leaving plutonium with atomic number 94
+and mass number 238. The radiochemical work leading to the
+isolation and identification of the atoms of element 96 was done
+at the metallurgical laboratory of the University of Chicago.</p>
+
+<p>The intense neutron flux available in modern reactors led to
+a new element, americium (Am), as follows:</p>
+
+<div class="figcenter" style="width: 438px;">
+<a name="Eqn_3" id="Eqn_3"><img src="images/eqn3.png" width="438" height="25" alt="[94]Pu[239] (n, &gamma;) [94]Pu[240] (n, &gamma;) [94]Pu[241] &beta; &rarr; [95]Am[241]." title="[94]Pu[239] (n, &gamma;) [94]Pu[240] (n, &gamma;) [94]Pu[241] &beta; &rarr; [95]Am[241]." /></a>
+</div>
+
+<p>The notation (n, &gamma;) means that the plutonium absorbs a neutron
+and gives off some energy in the form of gamma rays (very hard x
+rays); it first forms <sub>94</sub>Pu<sup>240</sup> and then <sub>94</sub>Pu<sup>241</sup>, which is unstable and
+gives off fast electrons (&beta;), leaving <sub>95</sub>Am<sup>241</sup>.</p>
+
+<p>Berkelium and californium, elements 97 and 98, were produced
+at the University of California by methods analogous to
+that used for curium, as shown in the following equations:</p>
+
+<div class="figcenter">
+<a name="Eqn_4" id="Eqn_4"><img src="images/eqn4.png" width="293" height="24" alt="[95]Am[240] + &alpha; &rarr; [97]Bk[243] + [0]n[1]," title="[95]Am[240] + &alpha; &rarr; [97]Bk[243] + [0]n[1]," /></a>
+</div>
+
+<p>and</p>
+
+<div class="figcenter">
+<a name="Eqn_5" id="Eqn_5"><img src="images/eqn5.png" width="288" height="23" alt="[96]Cm[241] + &alpha; &rarr; [98]Cf[244] + [0]n[1]." title="[96]Cm[241] + &alpha; &rarr; [98]Cf[244] + [0]n[1]." /></a>
+</div>
+
+<p>The next two elements, einsteinium (<sub>99</sub>Es) and fermium
+(<sub>100</sub>Fm), were originally found in the debris from the thermonuclear
+device "Mike," which was detonated on Eniwetok atoll
+November 1952. (This method of creating new substances is somewhat
+more extravagant than the mythical Chinese method of
+burning down a building to get a roast pig.)</p>
+
+<p>These elements have since been made in nuclear reactors and
+by bombardment. This time the "bullet" was N<sup>14</sup> stripped of
+electrons till it had a charge of +6, and the target was plutonium.</p>
+
+<div><span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span></div><p>Researchers at the University of California used new techniques
+in forming and identifying element 101, mendelevium. A
+very thin layer of <sub>99</sub>Es<sup>253</sup> was electroplated onto a thin gold foil
+and was then bombarded, from behind the layer, with 41-MeV &alpha;
+particles. Unchanged <sub>99</sub>Es<sup>253</sup> stayed on the gold, but those atoms
+hit by &alpha; particles were knocked off and deposited on a "catcher"
+gold foil, which was then dissolved and analyzed (Fig. 3). This
+freed the new element from most of the very reactive parent substances,
+so that analysis was easier. Even so, the radioactivity
+was so weak that the new element was identified "one atom at a
+time"; this is possible because its daughter element, fermium,
+spontaneously fissions and releases energy in greater bursts than
+any possible contaminant.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a href="images/fig3_1200.png"><img src="images/fig3_600.png" width="600" height="312" alt="Fig. 3. The production of mendelevium." title="" /></a>
+<span class="caption">Fig. 3. The production of mendelevium.</span>
+</div>
+
+<p>In 1957, in Stockholm, element 102 was reported found by
+an international team of scientists (who called it nobelium), but
+diligent and extensive research failed to duplicate the Stockholm
+findings. However, a still newer technique developed at Berkeley
+showed the footprints&mdash;if not the living presence&mdash;of 102 (see
+Fig. 4). The rare isotope curium-246 is coated on a small piece of
+nickel foil, enclosed in a helium-filled container, and placed in the<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span>
+heavy-ion linear accelerator (Hilac) beam. Positively charged atoms
+of element 102 are knocked off the foil by the beam, which is of
+carbon-12 or carbon-13 nuclei, and are deposited on a negatively
+charged conveyor apron. But element 102 doesn't live long enough
+to be actually measured. As it decays, its daughter product,
+<sub>100</sub>Fm<sup>250</sup>, is attracted onto a charged aluminum foil where it can be
+analyzed. The researchers have decided that the hen really did
+come first: they have the egg; therefore the hen must have existed.
+By measuring the time distance between target and daughter
+product, they figure that the hen-mother (element 102) must have
+a half-life of three seconds.</p>
+
+<div class="figcenter" style="width: 600px;">
+<a href="images/fig4_1200.png"><img src="images/fig4_600.png" width="600" height="327" alt="Fig. 4. The experimental arrangement
+used in the discovery of element 102." title="" /></a>
+<span class="caption">Fig. 4. The experimental arrangement
+used in the discovery of element 102.</span>
+</div>
+
+<p>In an experiment completed in 1961, researchers at the
+University of California at Berkeley unearthed similar "footprints"
+belonging to element 103 (named lawrencium in honor of Nobel
+prizewinner Ernest O. Lawrence). They found that the bombardment
+of californium with boron ions released &alpha; particles which
+had an energy of 8.6 MeV and decayed with a half-life of 8 &plusmn; 2
+seconds. These particles can only be produced by element 103,
+which, according to one scientific theory, is a type of "dinosaur"
+of matter that died out a few weeks after creation of the universe.</p>
+
+<div><span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span></div><p>The half-life of lawrencium (Lw) is about 8 seconds, and its
+mass number is thought to be 257, although further research is
+required to establish this conclusively.</p>
+
+<p>Research on lawrencium is complicated. Its total &alpha; activity
+amounts to barely a few counts per hour. And, since scientists
+had the &alpha;-particle "footprints" only and not the beast itself, the
+complications increased. Therefore no direct chemical techniques
+could be used, and element 103 was the first to be discovered solely
+by nuclear methods.<a name="FNanchor_A_1" id="FNanchor_A_1"></a><a href="#Footnote_A_1" class="fnanchor">[A]</a></p>
+
+<p>For many years the periodic system was considered closed
+at 92. It has now been extended by at least eleven places (Table I),
+and one of the extensions (plutonium) has been made in truckload
+lots. Its production and use affect the life of everyone in the
+United States and most of the world.</p>
+
+<p>Surely the end is again in sight, at least for ordinary matter,
+although persistent scientists may shift their search to the other-world
+"anti" particles. These, too, will call for very special
+techniques for detection of their fleeting presence.</p>
+
+<p>Early enthusiastic researchers complained that a man's life
+was not long enough to let him do all the work he would like on
+an element. The situation has now reached a state of equilibrium;
+neither man nor element lives long enough to permit all the
+desired work.</p>
+
+<div class="footnote"><p><a name="Footnote_A_1" id="Footnote_A_1"></a><a href="#FNanchor_A_1"><span class="label">[A]</span></a> In August 1964 Russian scientists claimed that
+they created element 104 with a half-life of about
+0.3 seconds by bombarding plutomium with accelerated
+neon-22 ions.</p></div>
+
+<hr style="width: 65%;" />
+<div><span class='pagenum'><a name="Page_12" id="Page_12">[<i>Pg 12</i>]</a></span></div>
+<div class="figcenter" style="width: 600px;">
+<span class="caption">Table I. THE TRANSURANIUM ELEMENTS</span></div>
+
+<table>
+<tr class="toprow">
+  <td style="width:100px">Element</td>
+  <td style="width:150px">Name (Symbol)</td>
+  <td style="width:100px">Mass Number</td>
+  <td style="width:300px">Year Discovered; by whom; where; how</td>
+</tr><tr class="midrow">
+  <td>93</td>
+  <td>Neptunium (Np)</td>
+  <td>238</td>
+  <td>1940; E. M. McMillan, P. H. Abelson; University of California at Berkeley; slow-neutron bombardment of U<sup>238</sup> in the 60-inch cyclotron.</td>
+</tr><tr class="midrow-noline">
+  <td>94</td>
+  <td>Plutonium (Pu)</td>
+  <td>238</td>
+  <td>1941; J. W. Kennedy, E. M.McMillan, G. T. Seaborg, and A. C. Wahl; University of California at Berkeley; 16-MeV deuteron bombardment of U<sup>238</sup> in the 60-inch cyclotron.</td>
+</tr><tr class="midrow">
+  <td>&nbsp;</td>
+  <td><span class="invisible">Plutonium</span> (Pu)</td>
+  <td>239</td>
+  <td>Pu<sup>239</sup>; the fissionable isotope of plutonium, was also discovered in 1941 by J. W. Kennedy, G. T. Seaborg, E. Segr&egrave; and A. C. Wahl; University of California at Berkeley; slow-neutron bombardment of U<sup>238</sup> in the 60-inch cyclotron.</td>
+</tr><tr class="midrow">
+  <td>95</td>
+  <td>Americium (Am)</td>
+  <td>241</td>
+  <td>1944-45; Berkeley scientists A. Ghiorso, R. A. James, L. O. Morgan, and G. T. Seaborg at the University of Chicago; intense neutron bombardment of plutonium in nuclear reactors.</td>
+</tr><tr class="midrow">
+  <td>96</td>
+  <td>Curium (Cm)</td>
+  <td>242</td>
+  <td>1945; Berkeley scientists A. Ghiorso, R. A. James, and G. T. Seaborg at the University of Chicago; bombardment of Pu<sup>239</sup> by 32-MeV helium ions from the 60-inch cyclotron.</td>
+</tr><tr class="midrow">
+  <td>97</td>
+  <td>Berkelium (Bk)</td>
+  <td>243</td>
+  <td>1949; S. G. Thompson, A. Ghiorso, and G. T. Seaborg; University of California at Berkeley; 35-MeV helium-ion bombardment of Am<sup>241</sup>.</td>
+</tr><tr class="midrow">
+  <td>98</td>
+  <td>Californium (Cf)</td>
+  <td>245</td>
+  <td>1950; S. G. Thompson, K. Street, A. Ghiorso, G. T. Seaborg; University of California at Berkeley; 35-MeV helium-ion bombardment of Cm<sup>242</sup>.</td>
+</tr><tr class="midrow">
+  <td><span class='pagenum'><a name="Page_13" id="Page_13">[<i>Pg 13</i>]</a></span>99<br />100</td>
+  <td>Einsteinium (Es)<br />Fermium (Fm)</td>
+  <td>253<br />255</td>
+  <td>1952-53; A. Ghiorso, S. G. Thompson, G. H. Higgins, G. T. Seaborg, M. H. Studier, P. R. Fields, S. M. Fried, H. Diamond, J. F. Mech, G. L. Pyle, J. R. Huizenga, A. Hirsch, W. M. Manning, C. I. Browne, H. L. Smith, R. W. Spence; "Mike" explosion in South Pacific; work done at University of California at Berkeley, Los Alamos Scientific Laboratory, and Argonne National Laboratory; both elements created by multiple capture of neutrons in uranium of first detonation of a thermonuclear device. The elements were chemically isolated from the debris of the explosion.</td>
+</tr><tr class="midrow">
+  <td>101</td>
+  <td>Mendelevium (Md)</td>
+  <td>256</td>
+  <td>1955; A. Ghiorso, B. G. Harvey, G. R. Choppin, S. G. Thompson, G. T. Seaborg; University of California at Berkeley; 41-MeV helium-ion bombardment of Es<sup>253</sup> in 60-inch cyclotron.</td>
+</tr><tr class="midrow">
+  <td>102</td>
+  <td>Unnamed<a name="FNanchor_B_2" id="FNanchor_B_2"></a><a href="#Footnote_B_2" class="fnanchor">[B]</a></td>
+  <td>254</td>
+  <td>1958; A. Ghiorso, T. Sikkeland, A. E. Larsh, R. M. Latimer; University of California, Lawrence Radiation Laboratory, Berkeley; 68-MeV carbon-ion bombardment of Cm<sup>246</sup> in heavy-ion linear accelerator (Hilac).</td>
+</tr><tr class="botrow">
+  <td>103</td>
+  <td>Lawrencium</td>
+  <td>257</td>
+  <td>1961; A. Ghiorso, T. Sikkeland, A. E. Larsh, R. M. Latimer; University of California, Lawrence Radiation Laboratory, Berkeley; 70-MeV boron-ion bombardment of Cf<sup>250</sup>, Cf<sup>251</sup>, and Cf<sup>252</sup> in Hilac.</td>
+</tr>
+</table>
+
+<div class="footnote"><p><a name="Footnote_B_2" id="Footnote_B_2"></a><a href="#FNanchor_B_2"><span class="label">[B]</span></a> A 1957 claim for the synthesis and identification of element 102 was accepted at that time by
+the International Union of Pure and Applied Chemistry, and the name nobelium (symbol No) was
+adopted. The University of California scientists, A. Ghiorso et al., cited here believe they have
+disproved the earlier claim and have the right to suggest a different name for the element.</p></div>
+
+<div class="figcenter" style="width: 800px;">
+<img src="images/bcover.png" width="383" height="600" alt="Back Cover: A Brief History of Element Discovery, Synthesis, and Analysis" title="" />
+<img src="images/fcover.png" width="383" height="600" alt="Front Cover: A Brief History of Element Discovery, Synthesis, and Analysis" title="" />
+</div>
+
+<div id="tnote"><h4>Transcriber's Note</h4>
+Table I (The Transuranium Elements) was originally located in the middle of the text on pages <a href="#Page_12">12</a>-<a href="#Page_13">13</a>.
+To improve readability of the e-book text, it has been relocated to the end of the text.<br />
+<br />
+The following errors are noted, but left as printed:<br />
+<div class="blockquot">
+<a href="#Page_8">Page 8</a>: "knowns" should be "knows"<br />
+<a href="#FNanchor_B_2">Page 17, footnote B</a>: "plutomium" should be "plutonium"<br />
+A more accurate rendering of the <a href="#Eqn_2">equation</a> on <a href="#Page_11">page 11</a> would be<br />
+<a name="Eqn_2-alt" id="Eqn_2-alt"><img src="images/eqn2-alt.png" width="354" height="35" alt="[94]Pu[239] (&alpha;, n) [96]Cm[242] &alpha;/150 days &rarr; [94]Pu[238]" title="[94]Pu[239] (&alpha;, n) [96]Cm[242] &alpha;/150 days &rarr; [94]Pu[238]" /></a>
+</div></div>
+
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
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+</pre>
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+The Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: A Brief History of Element Discovery, Synthesis, and Analysis
+
+Author: Glen W. Watson
+
+Release Date: March 13, 2010 [EBook #31624]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK ELEMENT DISCOVERY ***
+
+
+
+
+Produced by Mark C. Orton, Erica Pfister-Altschul and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+[Transcriber's Notes: The following errors are noted, but have not been
+corrected:
+
+    Page 17, footnote: "plutomium" should be "plutonium"
+    Page 8: "knowns" should be "knows"
+
+In element names, {} represents subscripted numbers and <> represents
+superscripted numbers. Readers may also refer to the HTML version of the
+text, in which super and subscripted numbers are represented visually.
+
+Italic emphasis is indicated by surrounding the word with _underscores_.
+
+Greek letters in the original text are marked in brackets, e. g. [alpha]
+or [gamma].
+
+Table I (THE TRANSURANIUM ELEMENTS) has been moved from pages 12-13, in
+the middle of the book, to the end of the text.]
+
+
+
+
+    A Brief History
+    of
+    ELEMENT DISCOVERY,
+    SYNTHESIS, and ANALYSIS
+
+
+    Glen W. Watson
+    September 1963
+
+    [Illustration]
+
+    LAWRENCE RADIATION LABORATORY
+    University of California
+    Berkeley and Livermore
+
+
+    Operating under contract with the
+    United States Atomic Energy Commission
+
+[Illustration: Radioactive elements: alpha particles from a speck of
+radium leave tracks on a photographic emulsion. (Occhialini and Powell,
+1947)]
+
+
+
+
+A BRIEF HISTORY OF ELEMENT DISCOVERY, SYNTHESIS, AND ANALYSIS
+
+
+It is well known that the number of elements has grown from four in the
+days of the Greeks to 103 at present, but the change in methods needed
+for their discovery is not so well known. Up until 1939, only 88
+naturally occurring elements had been discovered. It took a dramatic
+modern technique (based on Ernest O. Lawrence's Nobel-prize-winning atom
+smasher, the cyclotron) to synthesize the most recently discovered
+elements. Most of these recent discoveries are directly attributed to
+scientists working under the Atomic Energy Commission at the University
+of California's Radiation Laboratory at Berkeley.
+
+But it is apparent that our present knowledge of the elements stretches
+back into history: back to England's Ernest Rutherford, who in 1919
+proved that, occasionally, when an alpha particle from radium strikes a
+nitrogen atom, either a proton or a hydrogen nucleus is ejected; to the
+Dane Niels Bohr and his 1913 idea of electron orbits; to a once unknown
+Swiss patent clerk, Albert Einstein, and his now famous theories; to
+Poland's Marie Curie who, in 1898, with her French husband Pierre
+laboriously isolated polonium and radium; back to the French scientist
+H. A. Becquerel, who first discovered something he called a "spontaneous
+emission of penetrating rays from certain salts of uranium"; to the
+German physicist W. K. Roentgen and his discovery of x rays in 1895; and
+back still further.
+
+During this passage of scientific history, the very idea of "element"
+has undergone several great changes.
+
+The early Greeks suggested earth, air, fire, and water as being the
+essential material from which all others were made. Aristotle considered
+these as being combinations of four properties: hot, cold, dry, and
+moist (see Fig. 1).
+
+[Illustration: Fig. 1. The elements as proposed by the early Greeks.]
+
+Later, a fifth "essence," ether, the building material of the heavenly
+bodies was added.
+
+Paracelsus (1493-1541) introduced the three alchemical symbols salt,
+sulfur, and mercury. Sulfur was the principle of combustability, salt
+the fixed part left after burning (calcination), and mercury the
+essential part of all metals. For example, gold and silver were
+supposedly different combinations of sulfur and mercury.
+
+Robert Boyle in his "Sceptical Chymist" (1661) first defined the word
+element in the sense which it retained until the discovery of
+radioactivity (1896), namely, a form of matter that could not be split
+into simpler forms.
+
+The first discovery of a true element in historical time was that of
+phosphorus by Dr. Brand of Hamburg, in 1669. Brand kept his process
+secret, but, as in modern times, knowledge of the element's existence
+was sufficient to let others, like Kunkel and Boyle in England, succeed
+independently in isolating it shortly afterward.
+
+As in our atomic age, a delicate balance was made between the
+"light-giving" (desirable) and "heat-giving" (feared) powers of a
+discovery. An early experimenter was at first "delighted with the white,
+waxy substance that glowed so charmingly in the dark of his laboratory,"
+but later wrote, "I am not making it any more for much harm may come of
+it."
+
+Robert Boyle wrote in 1680 of phosphorus, "It shone so briskly and lookt
+so oddly that the sight was extreamly pleasing, having in it a mixture
+of strangeness, beauty and frightfulness."
+
+These words describe almost exactly the impressions of eye witnesses of
+the first atom bomb test at Alamagordo, New Mexico, July 16, 1945.
+
+For the next two and three-quarters centuries the chemists had much fun
+and some fame discovering new elements. Frequently there was a long
+interval between discovery and recognition. Thus Scheele made chlorine
+in 1774 by the action of "black manganese" (manganese dioxide) on
+concentrated muriatic acid (hydrochloric acid), but it was not
+recognized as an element till the work of Davy in 1810.
+
+Occasionally the development of a new technique would lead to the "easy"
+discovery of a whole group of new elements. Thus Davy, starting in 1807,
+applied the method of electrolysis, using a development of Volta's pile
+as a source of current; in a short time he discovered aluminum, barium,
+boron, calcium, magnesium, potassium, sodium, and strontium.
+
+The invention of the spectroscope by Bunsen and Kirchhoff in 1859
+provided a new tool which could establish the purity of substances
+already known and lead to the discovery of others. Thus, helium was
+discovered in the sun's spectrum by Jansen and isolated from uranite by
+Ramsay in 1895.
+
+The discovery of radioactivity by Becquerel in 1896 (touched off by
+Roentgen's discovery of x rays the year before) gave an even more
+sensitive method of detecting the presence or absence of certain kinds
+of matter. It is well known that Pierre and Marie Curie used this
+new-found radioactivity to identify the new elements polonium and
+radium. Compounds of these new elements were obtained by patient
+fractional recrystallization of their salts.
+
+The "explanation" of radioactivity led to the discovery of isotopes by
+Rutherford and Soddy in 1914, and with this discovery a revision of our
+idea of elements became necessary. Since Boyle, it had been assumed that
+all atoms of the individual elements were identical and unlike any
+others, and could not be changed into anything simpler. Now it became
+evident that the atoms of radioactive elements were constantly changing
+into other elements, thereby releasing very large amounts of energy, and
+that many different forms of the same element (lead was the first
+studied) were possible. We now think of an element as a form of matter
+in which all atoms have the same nuclear charge.
+
+The human mind has always sought order and simplification of the
+external world; in chemistry the fruitful classifications were
+Dobereiner's Triads (1829), Newland's law of octaves (1865), and
+Mendeleev's periodic law (1869). The chart expressing this periodic law
+seemed to indicate the maximum extent of the elements and gave good
+hints "where to look for" and "the probable properties of" the remaining
+ones (see Fig. 2).
+
+By 1925, all but four of the slots in the 92-place file had been filled.
+The vacancies were at 43, 61, 85, and 87.
+
+[Illustration: Fig. 2. Periodic chart of the elements (1963)]
+
+Workers using traditional analytical techniques continued to search for
+these elements, but their efforts were foredoomed to failure. None of
+the nuclei of the isotopes of elements 43, 61, 85, and 87 are stable;
+hence weighable quantities of them do not exist in nature, and new
+techniques had to be developed before we could really say we had
+"discovered" them.
+
+In 1919, Rutherford accomplished scientifically what medieval alchemists
+had failed to do with "magic" experiments and other less sophisticated
+techniques. It wasn't gold (the goal of the alchemists) he found but
+something more valuable with even greater potential for good and evil: a
+method of transmuting one element into another. By bombarding nitrogen
+nuclei with alpha particles from radium, he found that nitrogen was
+changed into oxygen.
+
+The process for radioactive transmutation is somewhat like a common
+chemical reaction. An alpha particle, which has the same charge (+2) and
+atomic mass (4) as a helium nucleus, penetrates the repulsive forces of
+the nitrogen nucleus and deposits one proton and one neutron; this
+changes the nitrogen atom into an oxygen atom. The reaction is written
+
+    {7}N<14> + {2}He<4> --> {1}H<1> + {8}O<17>.
+
+The number at the lower left of each element symbol in the above
+reaction is the proton number. This number determines the basic chemical
+identity of an atom, and it is this number scientists must change before
+one element can be transformed into another. The common way to
+accomplish this artificially is by bombarding nuclei with nuclear
+projectiles.
+
+Rutherford used naturally occurring alpha particles from radium as his
+projectiles because they were the most effective he could then find. But
+these natural alpha particles have several drawbacks: they are
+positively charged, like the nucleus itself, and are therefore more or
+less repulsed depending on the proton number of the element being
+bombarded; they do not move fast enough to penetrate the nuclei of
+heavier elements (those with many protons); and, for various other
+reasons (some of them unexplained), are inefficient in breaking up the
+nucleus. It is estimated that only 1 out of 300,000 of these alpha
+particles will react with nitrogen.
+
+Physicists immediately began the search for artificial means to
+accelerate a wider variety of nuclear particles to high energies.
+
+Protons, because they have a +1 charge rather than the +2 charge of the
+alpha particles, are repulsed less strongly by the positive charge on
+the nucleus, and are therefore more useful as bombarding projectiles. In
+1929, E. T. S. Walton and J. D. Cockcroft passed an electric discharge
+through hydrogen gas, thereby removing electrons from the hydrogen atom;
+this left a beam of protons (i. e., hydrogen ions), which was then
+accelerated by high voltages. This Cockcroft-Walton voltage multiplier
+accelerated the protons to fairly high energies (about 800,000 electron
+volts), but the protons still had a plus charge and their energies were
+still not high enough to overcome the repulsive forces (Coulombic
+repulsion) of the heavier nuclei.
+
+A later development, the Van de Graaff electrostatic generator, produced
+a beam of hydrogen ions and other positively charged ions, and electrons
+at even higher energies. An early model of the linear accelerator also
+gave a beam of heavy positive ions at high energies. These were the next
+two instruments devised in the search for efficient bombarding
+projectiles. However, the impasse continued: neither instrument allowed
+scientists to crack the nuclei of the heavier elements.
+
+Ernest O. Lawrence's cyclotron, built in 1931, was the first device
+capable of accelerating positive ions to the very high energies needed.
+Its basic principle of operation is not difficult to understand. A
+charged particle accelerated in a cyclotron is analogous to a ball being
+whirled on a string fastened to the top of a pole. A negative electric
+field attracts the positively charged particle (ball) towards it and
+then switches off until the particle swings halfway around; the field
+then becomes negative in front of the particle again, and again attracts
+it. As the particle moves faster and faster it spirals outward in an
+ever increasing circle, something like a tether ball unwinding from a
+pole. The energies achieved would have seemed fantastic to earlier
+scientists. The Bevatron, a modern offspring of the first cyclotron,
+accelerates protons to 99.13% the speed of light, thereby giving them
+6.2 billion electron volts (BeV).
+
+Another instrument, the heavy-ion linear accelerator (Hilac),
+accelerates ions as heavy as neon to about 15% the speed of light. It is
+called a linear accelerator because it accelerates particles in a
+straight line. Stanford University is currently (1963) in the process of
+building a linear accelerator approximately two miles long which will
+accelerate charged particles to 99.9% the speed of light.
+
+But highly accelerated charged particles did not solve all of science's
+questions about the inner workings of the nucleus.
+
+In 1932, during the early search for more efficient ways to bombard
+nuclei, James Chadwick discovered the neutron. This particle, which is
+neutral in charge and is approximately the same mass as a proton, has
+the remarkable quality of efficiently producing nuclear reactions even
+at very low energies. No one exactly knowns why. At low energies,
+protons, alpha particles, or other charged particles do not interact
+with nuclei because they cannot penetrate the electrostatic energy
+barriers. For example, slow positive particles pick up electrons, become
+neutral, and lose their ability to cause nuclear transformations. Slow
+neutrons, on the other hand, can enter nearly all atomic nuclei and
+induce fission of certain of the heavier ones. It is, in fact, these
+properties of the neutron which have made possible the utilization of
+atomic energy.
+
+With these tools, researchers were not long in accurately identifying
+the missing elements 43, 61, 85, and 87 and more--indeed, the list of
+new elements, isotopes, and particles now seems endless.
+
+Element 43 was "made" for the first time as a result of bombarding
+molybdenum with deuterons in the Berkeley cyclotron. The chemical work
+of identifying the element was done by Emilio Segre and others then
+working at Palermo, Sicily, and they chose to call it technetium,
+because it was the element first made by artificial technical methods.
+
+Element 61 was made for the first time from the fission disintegration
+products of uranium in the Clinton (Oak Ridge) reactor. Marinsky and
+Glendenin, who did the chemical work of identification, chose to call it
+promethium because they wished to point out that just as Prometheus
+stole fire (a great force for good or evil) from the hidden storehouse
+of the gods and presented it to man, so their newly assembled reactor
+delivered to mankind an even greater force, nuclear energy.
+
+Element 85 is called astatine, from the Greek astatos, meaning
+"unstable," because astatine _is_ unstable (of course all other elements
+having a nuclear charge number greater than 84 are unstable, too).
+Astatine was first made at Berkeley by bombarding bismuth with alpha
+particles, which produced astatine and released two neutrons. The
+element has since been found in nature as a small constituent of the
+natural decay of actinium.
+
+The last of the original 92 elements to be discovered was element 87,
+francium. It was identified in 1939 by French scientist Marguerite
+Perey.
+
+Children have a game in which they pile blocks up to see how high they
+can go before they topple over. In medieval times, petty rulers in their
+Italian states vied with one another to see who could build the tallest
+tower. Some beautiful results of this game still remain in Florence,
+Siena, and other Italian hill cities. Currently, Americans vie in a
+similar way with the wheelbase and overall length of their cars. After
+1934, the game among scientists took the form of seeing who could extend
+the length of the periodic system of the elements; as with medieval
+towers, it was Italy that again began with the most enthusiasm and
+activity under the leadership of Enrico Fermi.
+
+Merely adding neutrons would not be enough; that would make only a
+heavier isotope of the already known heaviest elements, uranium.
+However, if the incoming neutron caused some rearrangement within the
+nucleus and if it were accompanied by expulsion of electrons, that
+_would_ make a new element. Trials by Fermi and his co-workers with
+various elements led to unmistakeable evidence of the expulsion of
+electrons (beta activity) with at least four different rates of decay
+(half-lives). Claims were advanced for the creation of elements 93 and
+94 and possibly further (the transuranium elements, Table I). Much
+difficulty was experienced, however, in proving that the activity really
+was due to the formation of elements 93 and 94. As more people became
+interested and extended the scope of the experiments, the picture became
+more confused rather than clarified. Careful studies soon showed that
+the activities did _not_ decay logarithmically--which means that they
+were caused by mixtures, not individual pure substances--and the
+original four activities reported by Fermi grew to at least nine.
+
+As a matter of fact, the way out of the difficulty had been indicated
+soon after Fermi's original announcement. Dr. Ida Noddack pointed out
+that no one had searched among the products of Fermi's experiment for
+elements _lighter_ than lead, but no one paid any attention to her
+suggestion at the time. The matter was finally cleared up by Dr. Otto
+Hahn and F. Strassmann. They were able to show that instead of uranium
+having small pieces like helium nuclei, fast electrons, and super-hard
+x-rays, knocked off as expected, the atom had split into two roughly
+equal pieces, together with some excess neutrons. This process is called
+nuclear fission. The two large pieces were unstable and decayed further
+with the loss of electrons, hence the [beta] activity. This process is
+so complicated that there are not, as originally reported, only four
+half-lives, but at least 200 different varieties of at least 35
+different elements. The discovery of fission attended by the release of
+enormous amounts of energy led to feverish activity on the part of
+physicists and chemists everywhere in the world. In June 1940, McMillan
+and Abelson presented definite proof that element 93 had been found in
+uranium penetrated by neutrons during deuteron bombardment in the
+cyclotron at the University of California Radiation Laboratory.
+
+The California scientists called the newly discovered element neptunium,
+because it lies beyond the element uranium just as the planet Neptune
+lies beyond Uranus. The particular isotope formed in those first
+experiments was {93}Np<239>; this is read neptunium having a nuclear charge
+of 93 and an atomic mass number of 239. It has a half-life of 2.3 days,
+during which it gives up another electron ([beta] particle) and becomes
+element 94, or plutonium (so called after Pluto, the next planet beyond
+Neptune). This particular form of plutonium ({94}Pu<239>) has such a long
+half-life (24,000 years) that it could not be detected. The first
+isotope of element 94 to be discovered was Pu<238>, made by direct deuteron
+bombardment in the Berkeley 60-inch cyclotron by Radiation Laboratory
+scientists Seaborg, McMillan, Kennedy, and Wahl; it had an [alpha]-decay
+half-life of 86.4 years, which gave it sufficient radioactivity so that
+its chemistry could be studied.
+
+Having found these chemical properties in Pu<238>, experimenters knew
+{94}Pu<239> would behave similarly. It was soon shown that the nucleus of
+{94}Pu<239> would undergo fission in the same way as {92}U<235> when
+bombarded with slow neutrons and that it could be produced in the newly
+assembled atomic pile. Researchers wished to learn as much as possible
+about its chemistry; therefore, during the summer of 1942 two large
+cyclotrons at St. Louis and Berkeley bombarded hundreds of pounds of
+uranium almost continuously. This resulted in the formation of 200
+micrograms of plutonium. From this small amount, enough of the chemical
+properties of the element were learned to permit correct design of the
+huge plutonium-recovery plant at Hanford, Washington. In the course of
+these investigations, balances that would weigh up to 10.5 mg with a
+sensitivity of 0.02 microgram were developed. The "test tubes" and
+"beakers" used had internal diameters of 0.1 to 1 mm and could measure
+volumes of 1/10 to 1/10,000 ml with an accuracy of 1%. The fact that
+there was no intermediate stage of experimentation, but a direct
+scale-up at Hanford of ten billion times, required truly heroic skill
+and courage.
+
+By 1944 sufficient plutonium was available from uranium piles (reactors)
+so that it was available as target material for cyclotrons. At Berkeley
+it was bombarded with 32-MeV doubly charged helium ions, and the
+following reactions took place:
+
+    {94}Pu<239> ([alpha], n) {96}Cm<242> [alpha] / 150 days --> {94}Pu<238>.
+
+This is to be read: plutonium having an atomic number of 94 (94
+positively charged protons in the nucleus) and a mass number of 239 (the
+whole atom weighs approximately 239 times as much as a proton), when
+bombarded with alpha particles (positively charged helium nuclei) reacts
+to give off a neutron and a new element, curium, that has atomic number
+96 and mass number 242. This gives off alpha particles at such a rate
+that half of it has decomposed in 150 days, leaving plutonium with
+atomic number 94 and mass number 238. The radiochemical work leading to
+the isolation and identification of the atoms of element 96 was done at
+the metallurgical laboratory of the University of Chicago.
+
+The intense neutron flux available in modern reactors led to a new
+element, americium (Am), as follows:
+
+    {94}Pu<239> (n, [gamma]) {94}Pu<240> (n, [gamma]) {94}Pu<241> [beta]
+            --> {95}Am<241>.
+
+The notation (n, [gamma]) means that the plutonium absorbs a neutron and
+gives off some energy in the form of gamma rays (very hard x rays); it
+first forms {94}Pu<240> and then {94}Pu<241>, which is unstable and gives
+off fast electrons ([beta]), leaving {95}Am<241>.
+
+Berkelium and californium, elements 97 and 98, were produced at the
+University of California by methods analogous to that used for curium,
+as shown in the following equations:
+
+    {95}Am<240> + [alpha] --> {97}Bk<243> + {0}n<1>,
+
+and {96}Cm<241> + [alpha] --> {98}Cf<244> + {0}n<1>.
+
+The next two elements, einsteinium ({99}Es) and fermium ({100}Fm), were
+originally found in the debris from the thermonuclear device "Mike,"
+which was detonated on Eniwetok atoll November 1952. (This method of
+creating new substances is somewhat more extravagant than the mythical
+Chinese method of burning down a building to get a roast pig.)
+
+These elements have since been made in nuclear reactors and by
+bombardment. This time the "bullet" was N<14> stripped of electrons till it
+had a charge of +6, and the target was plutonium.
+
+Researchers at the University of California used new techniques in
+forming and identifying element 101, mendelevium. A very thin layer of
+{99}Es<253> was electroplated onto a thin gold foil and was then bombarded,
+from behind the layer, with 41-MeV [alpha] particles. Unchanged {99}Es<253>
+stayed on the gold, but those atoms hit by [alpha] particles were
+knocked off and deposited on a "catcher" gold foil, which was then
+dissolved and analyzed (Fig. 3). This freed the new element from most of
+the very reactive parent substances, so that analysis was easier. Even
+so, the radioactivity was so weak that the new element was identified
+"one atom at a time"; this is possible because its daughter element,
+fermium, spontaneously fissions and releases energy in greater bursts
+than any possible contaminant.
+
+[Illustration: Fig. 3. The production of mendelevium.]
+
+In 1957, in Stockholm, element 102 was reported found by an
+international team of scientists (who called it nobelium), but diligent
+and extensive research failed to duplicate the Stockholm findings.
+However, a still newer technique developed at Berkeley showed the
+footprints--if not the living presence--of 102 (see Fig. 4). The rare
+isotope curium-246 is coated on a small piece of nickel foil, enclosed
+in a helium-filled container, and placed in the heavy-ion linear
+accelerator (Hilac) beam. Positively charged atoms of element 102 are
+knocked off the foil by the beam, which is of carbon-12 or carbon-13
+nuclei, and are deposited on a negatively charged conveyor apron. But
+element 102 doesn't live long enough to be actually measured. As it
+decays, its daughter product, {100}Fm<250>, is attracted onto a charged
+aluminum foil where it can be analyzed. The researchers have decided
+that the hen really did come first: they have the egg; therefore the hen
+must have existed. By measuring the time distance between target and
+daughter product, they figure that the hen-mother (element 102) must
+have a half-life of three seconds.
+
+[Illustration: Fig. 4. The experimental arrangement used in the
+discovery of element 102.]
+
+In an experiment completed in 1961, researchers at the University of
+California at Berkeley unearthed similar "footprints" belonging to
+element 103 (named lawrencium in honor of Nobel prizewinner Ernest O.
+Lawrence). They found that the bombardment of californium with boron
+ions released [alpha] particles which had an energy of 8.6 MeV and
+decayed with a half-life of 8 +- 2 seconds. These particles can only be
+produced by element 103, which, according to one scientific theory, is a
+type of "dinosaur" of matter that died out a few weeks after creation of
+the universe.
+
+The half-life of lawrencium (Lw) is about 8 seconds, and its mass number
+is thought to be 257, although further research is required to establish
+this conclusively.
+
+Research on lawrencium is complicated. Its total [alpha] activity
+amounts to barely a few counts per hour. And, since scientists had the
+[alpha]-particle "footprints" only and not the beast itself, the
+complications increased. Therefore no direct chemical techniques could
+be used, and element 103 was the first to be discovered solely by
+nuclear methods.[A]
+
+For many years the periodic system was considered closed at 92. It has
+now been extended by at least eleven places (Table I), and one of the
+extensions (plutonium) has been made in truckload lots. Its production
+and use affect the life of everyone in the United States and most of the
+world.
+
+Surely the end is again in sight, at least for ordinary matter, although
+persistent scientists may shift their search to the other-world "anti"
+particles. These, too, will call for very special techniques for
+detection of their fleeting presence.
+
+Early enthusiastic researchers complained that a man's life was not long
+enough to let him do all the work he would like on an element. The
+situation has now reached a state of equilibrium; neither man nor
+element lives long enough to permit all the desired work.
+
+[A] In August 1964 Russian scientists claimed that they created element
+104 with a half-life of about 0.3 seconds by bombarding plutomium with
+accelerated neon-22 ions.
+
+
+Table I. THE TRANSURANIUM ELEMENTS
+
+  ========================================================================
+  Element    Name (Symbol)     Mass     Year Discovered; by whom;
+                              Number          where; how
+  ------------------------------------------------------------------------
+     93     Neptunium (Np)      238    1940; E. M. McMillan, P. H.
+                                       Abelson; University of California
+                                       at Berkeley; slow-neutron
+                                       bombardment of U<238> in the
+                                       60-inch cyclotron.
+  ------------------------------------------------------------------------
+     94     Plutonium (Pu)      238    1941; J. W. Kennedy, E. M.
+                                       McMillan, G. T. Seaborg, and A. C.
+                                       Wahl; University of California at
+                                       Berkeley; 16-MeV deuteron
+                                       bombardment of U<238> in the
+                                       60-inch cyclotron.
+
+                      (Pu)      239    Pu<239>; the fissionable isotope
+                                       of plutonium, was also discovered
+                                       in 1941 by J. W. Kennedy, G. T.
+                                       Seaborg, E. Segre and A. C. Wahl;
+                                       University of California at
+                                       Berkeley; slow-neutron bombardment
+                                       of U<238> in the 60-inch
+                                       cyclotron.
+  ------------------------------------------------------------------------
+     95     Americium (Am)      241    1944-45; Berkeley scientists A.
+                                       Ghiorso, R. A. James, L. O.
+                                       Morgan, and G. T. Seaborg at the
+                                       University of Chicago; intense
+                                       neutron bombardment of plutonium
+                                       in nuclear reactors.
+  ------------------------------------------------------------------------
+     96     Curium (Cm)         242    1945; Berkeley scientists A.
+                                       Ghiorso, R. A. James, and G. T.
+                                       Seaborg at the University of
+                                       Chicago; bombardment of Pu<239>
+                                       by 32-MeV helium ions from the
+                                       60-inch cyclotron.
+  ------------------------------------------------------------------------
+     97     Berkelium (Bk)      243    1949; S. G. Thompson, A. Ghiorso,
+                                       and G. T. Seaborg; University of
+                                       California at Berkeley; 35-MeV
+                                       helium-ion bombardment of
+                                       Am<241>.
+  ------------------------------------------------------------------------
+     98     Californium (Cf)    245    1950; S. G. Thompson, K. Street,
+                                       A. Ghiorso, G. T. Seaborg;
+                                       University of California at
+                                       Berkeley; 35-MeV helium-ion
+                                       bombardment of Cm<242>.
+  ------------------------------------------------------------------------
+     99     Einsteinium (Es)    253    1952-53; A. Ghiorso, S. G.
+    100     Fermium (Fm)        255    Thompson, G. H. Higgins, G. T.
+                                       Seaborg, M. H. Studier, P. R.
+                                       Fields, S. M. Fried, H. Diamond,
+                                       J. F. Mech, G. L. Pyle, J. R.
+                                       Huizenga, A. Hirsch, W. M.
+                                       Manning, C. I. Browne, H. L.
+                                       Smith, R. W. Spence; "Mike"
+                                       explosion in South Pacific; work
+                                       done at University of California
+                                       at Berkeley, Los Alamos Scientific
+                                       Laboratory, and Argonne National
+                                       Laboratory; both elements created
+                                       by multiple capture of neutrons in
+                                       uranium of first detonation of a
+                                       thermonuclear device. The elements
+                                       were chemically isolated from the
+                                       debris of the explosion.
+  ------------------------------------------------------------------------
+    101     Mendelevium (Md)    256    1955; A. Ghiorso, B. G. Harvey, G.
+                                       R. Choppin, S. G. Thompson, G. T.
+                                       Seaborg; University of California
+                                       at Berkeley; 41-MeV helium-ion
+                                       bombardment of Es<253> in 60-inch
+                                       cyclotron.
+  ------------------------------------------------------------------------
+    102     Unnamed[B]          254    1958; A. Ghiorso, T. Sikkeland, A.
+                                       E. Larsh, R. M. Latimer;
+                                       University of California, Lawrence
+                                       Radiation Laboratory, Berkeley;
+                                       68-MeV carbon-ion bombardment of
+                                       Cm<246> in heavy-ion linear
+                                       accelerator (Hilac).
+  ------------------------------------------------------------------------
+    103     Lawrencium          257    1961; A. Ghiorso, T. Sikkeland, A.
+                                       E. Larsh, R. M. Latimer;
+                                       University of California, Lawrence
+                                       Radiation Laboratory, Berkeley;
+                                       70-MeV boron-ion bombardment of
+                                       Cf<250>, Cf<251>, and Cf<252>
+                                       in Hilac.
+  ========================================================================
+
+[B] A 1957 claim for the synthesis and identification of element 102 was
+accepted at that time by the International Union of Pure and Applied
+Chemistry, and the name nobelium (symbol No) was adopted. The University
+of California scientists, A. Ghiorso et al., cited here believe they
+have disproved the earlier claim and have the right to suggest a
+different name for the element.
+
+
+
+
+
+End of the Project Gutenberg EBook of A Brief History of Element Discovery,
+Synthesis, and Analysis, by Glen W. Watson
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