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Synthesis, and Analysis, by Glen W. Watson
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Title: A Brief History of Element Discovery, Synthesis, and Analysis
Author: Glen W. Watson
Release Date: March 13, 2010 [EBook #31624]
Language: English
*** 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 Segrè 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. Segrè 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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