210 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



The relatively low specific a-activity of the isotope Np^^ places the 

 element neptunium in a class by itself in the transuranium group 

 because it is relatively safe to handle from the health standpoint. 

 The other transuranium elements are so highly a-radioactive that spe- 

 cial techniques and precautions are mandatory when they are handled in 

 ordinary, let us say milligi-am, amounts. However, the half -life of 

 Np^% 2.25X10^ years, corresponds to a specific a-particle activity of 

 some 1% million a-particles per minute per milligram, only about 

 1,000 times that of ordinary uranium. Material of this level of radio- 

 activity can be handled without special equipment, provided reasonable 

 care and precautions are observed. 



It seems desirable to work toward the modification of the chemical 

 separation processes used in the plutonium manufacturing plants in 

 such a manner that the neptunium will be completely recovered in a 

 routine manner and it seems likely that this will be done sometime in 

 the future. When neptunium becomes available in moderate amounts, 

 one can visualize its eventual classification as an element whose avail- 

 ability to chemists as a whole for study will rank along with a number 

 of the rarer elements in the classical periodic table. In fact, it is not 

 out of the question that neptunium may some day be used sparingly 

 in university laboratory courses in qualitative analysis and advanced 

 inorganic chemistry and in courses in nuclear chemistry and physics. 



PLUTONIUM 



Plutonium was the second transuranium element to be discovered. 

 The first isotope to be fund was Pu^, an a-emitter of some 50 years' 

 half-life, formed according to the following reactions: 



U^s-^ji^ , Np238^2n (4) 



Np238 . , Pu238 (5) 



2.0-day 



The chemistry of plutonium was first investigated by the tracer 

 technique using this isotope. These experiments showed that the 

 chemical properties of this element are similar to those of neptunium 

 and uranium, differing in that the lower oxidation states of plutonium 

 are more stable. 



The isotope of major importance is, of course, Pu^^^ This isotope, 

 which is an a-emitter with a half-life of about 24,000 years, is 

 synthesized according to reactions 1 and 2 above, and its tremendous 

 importance stems from its property of being fissionable with slow 

 neutrons, together with the fact that the problem of its mass production 

 has been solved. 



