Distribution of Energy in Different Types of y Rays. 527 



When v = 0, the pressure is equal to one-third of the energy 

 per unit volume due to the incident and reflected wave-trains 

 — the result used by Boltzmann in proving" Stefan's law. 

 When v is not negligible, but is so small that the second 

 term within the brackets may be neglected, the value o£ the 

 pressure is equal to 



1 2i_ 



'd'SlTC 2 ' C 



LV. On the Distribution of Energy in the Different Types 

 of y Rays emitted from Certain Radioactive Substances. 

 By Jadwiga Szmidt*. 



THE primary y radiation of all known radioactive sub- 

 stances has recently been examined by Rutherford and 

 Richardson f by measurement of its absorption in aluminium. 

 Most of the radio-elements have been found to emit two or 

 three different types of rays, differing widely in penetrating 

 power. The intensity of the different types also varies ; in 

 some cases (as in radium D) the softer rays predominating, 

 and in others the hard ones (as in radium B). The question 

 as to the relative amounts of energy associated with each 

 particular type of y rays has recently become important from 

 the point of view of the light it throws on the relation between 

 the /3 and y radiation, and indirectly on the internal structure 

 of the radioatoms involved. 



In the present investigation, therefore, an attempt has been 

 made to obtain an approximate knowledge of the distribution 

 of energy in the different types of y rays emitted by three 

 radioactive substances — radium B, radium C, and radium D. 

 The method used was to compare the total number of ions 

 each type of rays produces in air or other gas. This com- 

 parison gives directly the ratio of the energies in the different 

 types of y rays if we make the following assumptions : — 

 (1) that the same proportion of energy of the different y rays 

 is spent in ionization, either direct or indirect, (2) that the 

 energy required to produce an ion is the same for y rays 

 of different penetrating power. The first assumption is 

 difficult to test experimentally. Information with regard to 

 the second assumption may be obtained by a careful exami- 

 nation of the relative total ionization in gase* produced by 

 7 rays of different hardness. It is to be expected that if 



* Communicated by Sir Ernest Rutherford, F.R.S. 



f Rutherford and Richardson, Phil. Mag. xxv. p. 722 (1913) ; xxvi. 

 p. 324 (1913) ; xxvi. p. 937 (1913). Richardson, Phil. Mag. xxvii. p. 252 

 <1914). 



