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diff --git a/31624-8.txt b/31624-8.txt new file mode 100644 index 0000000..081bf2a --- /dev/null +++ b/31624-8.txt @@ -0,0 +1,1013 @@ +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. 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