Einsteinium and Fermium

After synthesis of californium scientists in America (and in other countries) started a serious reassessment of their plans. They asked whether it was reasonable to plan for syntheses of heavier transuranium elements in the foreseeable future. 

Indeed, there were no practicable methods for accumulation of berklium and californium in sufficient quantities to prepare targets to be bombarded by alpha particles as a means of synthesizing elements 99 and 100. This was due to short half-lives of berklium and californium measured in hours and minutes (long-lived isotopes were unknown at the time). There was only one more or less feasible method, namely, to bombard plutonium with a high-intensity neutron beam but then the results would be obtained only many years later. 

Of course, it would be desirable to obtain such a high-intensity neutron beam that would solve all the problems at once. If uranium or plutonium could capture a large number of neutrons in a short period they would convert into very heavy isotopes, for instance. 

It had long been known that nuclei get rid of excess neutrons by converting them into protons, that is, by way of beta decay. These chains of successive beta transformations can prove to be so long that they will lead to the formation of isotopes of elements 99 and 100. 

But according to calculations the intensities of neutron fluxes in nuclear reactors were too low to sustain such reactions. Moreover, theorists predicted short half-lives for the isotopes of elements 99 and 100. 

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The use of larger particles in the cyclotron, for example carbon, nitrogen or oxygen ions, enabled elements of several units of atomic number beyond uranium to be synthesised. Einsteinium and fermium were obtained by this method and separated by ion-exchange. and indeed first identified by the appearance of their concentration peaks on the elution graph at the places expected for atomic numbers 99 and 100. The concentrations available when this was done were measured not in gcm but in atoms cm. The same elements became available in greater quantity when the first hydrogen bomb was exploded, when they were found in the fission products. Element 101, mendelevium, was made by a-particle bombardment of einsteinium, and nobelium (102) by fusion of curium and the carbon-13 isotope. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

It is possible to prepare very heavy elements in thermonuclear explosions, owing to the very intense, although brief (order of a microsecond), neutron flux furnished by the explosion (3,13). Einsteinium and fermium were first produced in this way they were discovered in the fallout materials from the first thermonuclear explosion (the "Mike" shot) staged in the Pacific in November 1952. It is possible that elements having atomic numbers greater than 100 would have been found had the debris been examined very soon after the explosion. The preparative process involved is multiple neutron capture in the uranium in the device, which is followed by a sequence of beta decays. Eor example, the synthesis of EM in the Mike explosion was via the production of from followed by a long chain of short-Hved beta decays,... 

The effects of a rather distinct deformed shell at = 152 were clearly seen as early as 1954 in the alpha-decay energies of isotopes of californium, einsteinium, and fermium. In fact, a number of authors have suggested that the entire transuranium region is stabilized by shell effects with an influence that increases markedly with atomic number. Thus the effects of shell substmcture lead to an increase in spontaneous fission half-Hves of up to about 15 orders of magnitude for the heavy transuranium elements, the heaviest of which would otherwise have half-Hves of the order of those for a compound nucleus (lO " s or less) and not of milliseconds or longer, as found experimentally. This gives hope for the synthesis and identification of several elements beyond the present heaviest (element 109) and suggest that the peninsula of nuclei with measurable half-Hves may extend up to the island of stabiHty at Z = 114 andA = 184. 

H. G. Jackson Isotopes of Einsteinium and Fermium Produced by Neutron Irradiation of Plutonium. Report AECL-287. Phys. Rev. 102, 203 (1956). 

The complexity of the reactions involved in the bombardment of plutonium and the production of higher transuranium elements can be seen from the following scheme which indicates the method of synthesis of einsteinium and fermium ... 

But for chemists, the hydrogen bomb tests had a happier fallout too. Scientists at the Mike test collected coral from a nearby atoll contaminated with radioactive debris, and sent it to Berkeley for analysis. There the nuclear chemists found two new elements, with atomic numbers 99 and 100. They were named after two of the century s most creative physicists einsteinium and fermium. 

EINSTENIUM. CAS 7429-92-71. Chemical element symbol Es, at. no. 99. at. wt. 254 (mass number of the most stable isotope), radioactive metal of the Actinide series, also one of the Transuranium elements. Both einsteinium and fermium were formed tit a thermonuclear explosion that occurred in the South Pacific in 1952. The elements were identified by scientists from the University of California s Radiation Laboratory- the Argonnc National Laboratory, and the I. os Alamos Scientific Laboratory. It was observed that very heavy uranium isotopes which resulted from the action of the instantaneous neutron dux on uranium (contained in the explosive device) decayed to form Es and Fm. The probable electronic configuration of Es is... 

Einsteinium, the tenth member of the actinide series, was discovered in 1952. Einsteinium and fermium (element 100) were most unexpectedly produced... 

Investigation of the amalgamation behavior of trivalent actinides in acetate and citrate solutions by treatment with sodium amalgam showed that Bk(III) does not readily form an amalgam. This behavior is in contrast to that of the heavier actinides californium, einsteinium, and fermium, which readily amalgamate (216, 217). 

The berkelium, californium, einsteinium, and fermium products are then packaged and transferred from the main cell bank to other facilities in which they are purified further. 

There are other methods of preparing these same isotopes of einsteinium and fermium, and one of these involves the use of the chain-reacting atomic pile which produces a high intensity of bombarding neutrons. 

The original einsteinium isotope discovered in Enewetak fallout was Es with a half-life of 20 days. Eventually other einsteinium isotopes were created under controlled conditions. The longest-lived is Es, ty, = 275 days. The longest-lived isotope of fermium is Fm, ti/, = 100.5 days. Chemically speaking, einsteinium and fermium are... 

In the final design for the Super the heat to initiate the fusion reaction is provided by a fission reaction, and once ignited, the reaction spreads like a normal thermochemical reaction (such as combustion), hence thermonuclear. The first test of a thermonuclear device, code-named Mike, was in 1952, and it completely leveled the small atoll in the Marshall Islands on which it was detonated. This weapon may have fulfilled the prediction of Alfred Nobel Perhaps my factories will end war sooner than your peace conferences. - War in the 1950s became Cold and Limited. There was another bit of fallout from the Mike test, chemical instead of political Sifting through debris from the Mike explosion, scientists found elements number 99 and 100 einsteinium and fermium. 

Thus, the discoveries of einsteinium and fermium were, so to say, unplanned. 

Ghiorso A, Thompson SG, Hi ins GH et al (1955b) New elements einsteinium and fermium, atomic numbers... 

Einsteinium (Es) and fermium (Fm) were identified in 1952 in the radioactive debris from the Mike thermonuclear explosion that took place in the Pacific. Ion-exchange separation was applied, and the new elements, einsteinium and fermium, were isolated by processing larger amounts of the radioactive coral material (Ghiorso et al. 1955a). Chemical identification was made by ion-exchange separations, while isotopic assignments were made as the result of the... 

For the purpose of transmutation, the minor actinides of concern in spent fuel are neptunium, americium, and curium although small amounts of the higher actinides, berkeUum, californium, einsteinium, and fermium can be made under the right conditions. The reaction pathways leading to the production of the transuranium elements are given in Fig. 61.4. 

The elements with atomic numbers higher than 92, the transuranium elements are generally produced by bombarding suitable nuclei either with neutrons in a nuclear reactor or with accelerated positive particles. Elements 99 and 100 (einsteinium and fermium) were initially detected among the products of the first hydrogen bomb explosion in 1952. All the transuranium elements are artificial, with the exception of plutonium, one isotope of which is found in natural uranium and is formed as a result of neutron bombardment in the mineral deposit. Using... 

Though now produced in prolonged reactor irradiations, einsteinium and fermium were first detected in the debris of the 1952 above-ground thermonuclear explosion of the MIKE device [81]. In MIKE, uranium was subjected to an enormous flux of neutrons, and the r-process resulted in the production of heavy elements. One of the distinctions between the stellar r-process and the thermonuclear r-process is the time over which the neutron exposure is delivered. While... 

Hoff, R.W. Production of einsteinium and fermium in nuclear explosions. Lawrence Livermore LabOTaUny reprat UCRL-81566 (1978)... 

Very heavy elements have been detected under circumstances where very intense neutron fluxes were produced. Such is the case for a few microseconds after a thermonuclear explosion. Isotopes of einsteinium and fermium were first discovered in the debris of the first thermonuclear explosion detonated at Eniwetok Atoll in November 1952 [2,5]. It is possible that elements of atomic number greater than 100 might have been detected had the debris been examined immediately after the explosion. The route whereby elements of high atomic number are formed in the detonation of a thermonuclear device is again multiple neutron capture in which is a component of the device. Thus, the synthesis... 

In ethanol solution, californium, einsteinium, and fermium can also be reduced to the divalent state by Sm(II) or Yb(II) even if the solutions contain 15 % water [223, 224]. Attempts to reduce mendelevium further to the monovalent state, which would correspond to a filled f shell, appear to have failed, although this matter remains controversial [224] (see also Chapter 13). 

The citrate ion was the eluting agent used in the first isolation of berkelium and californium [189,190]. Soon afterwards, however, the lactate and tartrate ions were found to give considerably improved separations between americium(iii) and curium (ill) [191]. Lactate elution also proved superior to the classic citrate elution for the first isolation of einsteinium and fermium [188]. Later on, an even more selective eluant for actinide(iii) ions has been found in the a-hydroxyisobutyrate ion [192], With this ligand, very clean separations of the heavy actinide(iii) ions can be achieved, as illustrated in Fig. 21.12. The first isolation of mendelevium was achieved by this procedure [193]. 

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