Question of the Homogeneity of * -Rays. 727 



y-rays needed careful re-examination before any conclusion as 

 to their heterogeneity or homogeneity could be formed, and that 

 the shape o£ the curves and values o£ the absorption coefficients 

 depended greatly on then unknown disturbing influences. 

 A quantitative comparison of the ratio of the intensity of the 

 /3- to y-radiation for uranium and radium showed that the 

 y-rays were relatively about 60 times less intense for uranium 

 than for radium, and on account of the similarity of the 

 penetrating power of the radiations of the two elements it 

 was pointed out that the /3- and y-rays could hardly be 

 regarded any longer as interdependent phenomena. 



In Part I. of the present communication the absorption 

 curves of uranium y-rays for various substances up to thick- 

 ness equivalent to 1 cm. of lead are given and discussed. It 

 is concluded that although for certain metals, for example 

 zinc, the curve can be represented as the sum of two positive 

 exponential terms, one due to the "hard " y-rays previously 

 studied and another due to a " soft " y-ray with absorption 

 coefficient about 14 times greater, this explanation does not 

 hold good for other substances. In any case the supposed 

 soft y-radiation is relatively feeble and unimportant. 



In Part II. it is shown that with certain new experimental 

 dispositions the y-rays of radium are absorbed by lead as a 

 homogeneous non-seaWred radiation with a constant value for 

 the absorption coefficient X ( = 0\50) in the strict sense of the 

 equation dl/dT=— XI over the ichole range up to 7*7 cm. 

 In these experiments the ionization vessel takes the form of 

 two hemispheres with the radium at the centre and the 

 absorbing plates are in the form of truncated hemispheres, 

 this being a disposition for which the theoretical expressions 

 can be evaluated. For zinc hemispheres again some evidence 

 of a secondary penetrating radiation generated in the zinc, 

 with a value for A, about 45 times greater than for the 

 primary, has been obtained. The uranium y-ray curves 

 show, however, small departures from the theoretical over the 

 first part of the range. 



In Part III. further evidence of the homogeneity of the 

 y-rays of radium is given. The departures of the curve from 

 the simple exponential type both at the beginning and the 

 end of the range in lead are shown to be due to disturbing 

 factors. With regard to the departures at the end of the 

 range (Tuomikoski) a simple exponential law has been found, 

 with suitable means of measurement, to hold up to 22 cm. 

 of lead with a value for \, 0*498, practically identical with 

 that given in the earlier paper. These results and others in 

 this paper show that the y-rays are capable of measurement 



