214 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



The availability of this isotope of americium made it possible to 

 study the chemical properties of this element using the tracer tech- 

 nique. Deductions from this work led to the conclusion that this 

 element probably exists in aqueous solution in only the one oxidation 

 state, the III state. This is in line with the tendency toward the 

 stabilization of the lower oxidation states in going to the heavier ele- 

 ments in this region. 



It has recently been possible to isolate americium in the form of a 

 pure compound of this element. B. B. Cunningham, working at the 

 Metallurgical Laboratory, has succeeded in isolating this element and 

 in studying its chemical properties using a weighable amount on the 

 ultramicrochemical scale. This is a remarkable achievement in that 

 the amounts available here were even smaller than those in the case of 

 neptunium and plutonium. This, then, is the third synthetic element 

 which has been isolated in pure form. The work of Cunningham and 

 L. B. Werner with pure americium in aqueous solution has confirmed 

 the tracer work by showing that the III oxidation state is very stable 

 in solution and is the predominant and most important state. 



Americium, with its 500-year half-life, has a higher specific a-activ- 

 ity than even Pu^^^. Its specific a-activity amounts to some 7 billion 

 a disintegrations per minute per milligram. Thus even if this element 

 should become available in ordinary amounts, let us say, milligram 

 amounts, it will always be necessary to conduct its investigation with 

 special precautions and using the special techniques for handling 

 highly a-active material. The investigation of the chemical properties 

 of americium will demand investigators who are well trained with 

 handling highly a-active materials. 



CURIUM 



Curium was the third transuranium element to be discovered. The 

 first isotope of this element was the isotope, Cm^*^, which was identified 

 in 1944 by G. T. Seaborg, E. A. James, and A. Ghiorso at the Metal- 

 lurgical Laboratory as the result of its production in the Berkeley 

 60-inch cyclotron by the following reaction : 



Pu^^HjHe^ > Crn^'+n (9) 



The isotope, Cm^*^, is an a-paiticle emitter with a half -life of about 5 

 months. 



The availability of this isotope of curium made it possible to study 

 the chemical properties of this element by use of the tracer technique. 

 Extensive investigations have led to the conclusion that curium prob- 

 ably exists exclusively in the III oxidation state in aqueous solution. 

 It is carried quantitatively by the rare earth fluorides in precipitation 

 reactions and can be separated from them only with difficulty. 



