JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol.11 October 4. 1921 No. 16 



PHYSICS. — A radioactive quantity requiring a name.'^ N. Krnest 

 DoRSEY, Bureau of Standards. 



The problems that are encountered in the quantitative study of 

 radioactive materials and processes may be divided into two classes. 

 In one class will be placed the strictly chemical problems; such as, 

 the amount of the element that is contained in a ton of ore, the ratio 

 of the amounts of different elements that are found associated, the 

 atomic weights and the chemical properties of the several elements. 

 In the other class will be placed the problems that are primarily con- 

 cerned with radioactive phenomena; such as, the rate of transforma- 

 tion, the rate of emission of energy, the rate of production of alpha 

 or of beta particles or of gamma pulses. 



In problems of the first class one is concerned with the total weight 

 or with the total number of atoms present, and the amount of the 

 element may appropriately be expressed in grams or in terms of the 

 number (N) of atoms present. These problems do not differ in any 

 essential respect from those encountered in dealing with other ele- 

 ments ; the radioactiA^e properties of the element enter into the problem 

 mainly as a means by which different amounts of the material can be 

 compared. 



In problems of the second class the results may likewise be expressed 

 as functions of the total weight, or of the total number of atoms, of 

 the element present, but when this is done certain fundamental rela- 

 tions are obscured. Only a relatively small fraction (XA^ of the 

 atoms present take part in the phenomenon studied, and the thing 

 that is of fundamental interest is the effect produced per atom actively 

 concerned. It is in this eft'ect per active atom that information re- 

 garding the atomic forces, structure, and instability, and the way 

 these vary from element to element, are to be sought. In such prob- 

 lems one is concerned with the number of atoms that have trans- 

 formed in a certain time ; he is but incidentally interested in the pres- 

 ence of atoms that have remained untraiisformed. He wishes to know 



' Contril)ution from the Bureau of Standards. Received August I, 192L 



381 



