PLUTONIUM — SEABORG 215 



The isotope Cm^" is also formed as the result of the strong neutron 

 irradiation of Am-". The Am-*^ absorbs neutrons to form a short- 

 lived (18-hour half-life) yS-emitter, Am^*^, which in turn decays to the 

 Cm^". These nuclear reactions may be summarized as follows : 



Am'^'+n > Am ^*^-{-y (10) 



Am2*2 ,Cm2« (11) 



18-hr. 



Another isotope of curium is also known. The bombardment of 

 Pu239 with 44-Mev. helium ions leads to the production of the 1-month 

 a-emitting Cm^^" by the reaction : 



Pu23»-f-2He* > Cm'^^+Sn 



The relative yield of Cm-^" compared to the yield of Cm^*^ from re- 

 action 9 above increases with increasing energy of the helium ions. 



The element curium has not yet been isolated in the pure state and 

 therefore this is the only one of the four known transuranium ele- 

 ments for which this has not been done.^ It is, of course, of interest to 

 inquire whether it will be possible to do this in the future. Appar- 

 ently this will be difficult with the present isotopes, Cm^*^ or Cm^^, 

 since these have rather short half-lives — namely, approximately 5 

 months and 1 month, respectively. As has been the case for the other 

 three transuranium elements the first isolation of curium in the pure 

 state will probably take place as the result of work on the ultramicro- 

 chemical scale with microgram or less amounts of material. 



The isotope Cm^" with its 5-month half -life has a specific a-activity 

 corresponding to about 10" a disintegrations per minute per milligram. 

 This will mean that even 1 microgram will correspond to some 10^ 

 disintegrations per minute. A specific a-radioactivity of this magni- 

 tude gives rise to problems due to the aggregate recoil of submicro- 

 gram particles as a result of the tremendous rate of a-emission. Never- 

 theless, it seems entirely possible and even likely that curium, prob- 

 ably in the form of the longer-lived isotope Cm^*^, will be isolated in 

 the pure state as soon as the problem of its production in microgram 

 amounts is solved. Once this pure element is available in microgram 

 amounts it will be possible to study its chemistry by means of investi- 

 gations on the ultramicrochemical scale, although each measurement 

 in this case will be most difficult and laborious. Among the difficul- 

 ties here will be the rapid decomposition of the water in the solution, 

 the formation of hydrogen peroxide in the solution, heating of the 

 solution, and other effects. However, as in the cases of the other 



* Curium was Isolated In pure form In the fall of 1947 by L. B. Werner and J. Perlman 

 at the University of California. 



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