36-4 Mr. J. Crosby Chapman on 



efficient than radiator T. in producing such radiation. Two 

 sheets of paper were used to separate the gold leaves in 

 radiator I. so as to ensure in all parts a sufficient thickness to 

 -absorb the whole of the incident corpuscular energy. 

 The research resolves itself into three parts : — 



(1) to test the efficiency of the two X-radiators ; 



(2) to determine the penetrating power of the exciting 



primary beam ; 



(3) to investigate what fraction of the total corpuscular 



radiation produced in one gold leaf escapes from 

 that leaf. 



Efficiency of the two X-radiators. 

 The following were measured : — 



(a) the efficiency of radiator I. as a fluorescent X-ray 



producer ; 

 (p) the efficiency of radiator II. as a fluorescent X-ray 



producer ; 

 (c) the intensity of scattered radiation from the third 



radiator consisting only of paper. 



Using the results so obtained, the ratio of the efficiencies of 

 the radiators I. -f II. was calculated. It only remained to show 

 that the radiation which was being measured was actually 

 the gold characteristic radiation. In order to prove this the 

 absorption in aluminium of the radiations from the gold 

 radiators was determined, allowance being made for the 

 scattered radiation from the paper. No correction was 

 applied for the scattered radiation from the gold itself ; this 

 correction is of such a small order that in the experiment it 

 w r ould have served no purpose. The absorption coefficient 



/-) of these rays in aluminium was equal to 20*6, while 



the most accurate value of — for gold radiation in alumi- 



P 

 nium = 21*6, and this is after somewhat tedious corrections 

 have been applied. This near agreement of 20*6 and 21*6 

 showed that the radiation, the intensity of which was being 

 determined, was actually the gold radiation. 



The results obtained after subtraction of the scattered 

 radiation from the paper are given below in tabular form. 

 In each case the radiation when radiator I. was used is taken 

 .as the standard. 



