722 Dr. J. A. Crowther on "J" Radiation. 



In the present experiments one of the chambers, Gp, was 

 placed so as to receive the full primary beam, after it had 

 traversed the radiator. The other, C s , was placed at right 

 angles to the primary beam, and measured the intensity of 

 the radiation emitted by the radiator in this direction. The 

 radiator itself was placed with its plane at 45° to the primary 

 beam. Assuming that the primary and secondary radiations 

 are of the same quality, it can be shown that with the 

 radiator in this position the absorptions of the primary and 

 secondary radiations in the radiator are the same, and cor- 

 rection for absorption becomes unnecessaiy. The ratio of the 

 ionization current through C s to that through C p should thus 

 be proportional to the relative intensities of the secondary 

 and primary radiation. 



To investigate the relative absorbabilities of the primary 

 and secondary radiations, a pair of aluminium screens of 

 equal size and thickness were placed one in front of the 

 chamber C s and the other in front of Cp. If the two 

 radiations were of the same quality the absorption produced in 

 each beam should be the same, and the ratio of the ionization 

 currents should be unaltered. If, however, the secondary 

 rays were less penetrating than the primary the former 

 would be more strongly absorbed, and the ratio would 

 diminish. Experiments were made with pairs of screens of 

 different thicknesses. The following table (Table I.) gives 











Table 



I. 











At 



uminium 



Radiator 



•0: 



21 cm. thick. 





I. 



Thickness of 



absorbing screen. 



(cm.) 



II. 

 P 



lo 



III. 



s 





IV. 



lo 



Y. 

 Log. -. 



o-oo 







222 



•805 





2-316 



T-91 



0071 







179 



•712 





2-253 



T-S5 



0120 







154 



•657 





2-188 



TS2 



210 







123 



•G10 





2-090 



7-785 



the results obtained with an aluminium radiator O021 cm. 

 thick. The first column gives the thickness of the aluminium 

 screens placed in front ol the two chambers. The second 

 column gives the ratio of the current through the chamber 

 C_p to that through the ionization chamber A, and thus affords 

 a measure of the absorption of the primary rays in the 



