D3r> 



Mr. D. C. H. Florance 



on 



Two narrow blocks of lead, each 1*5 cm. thick, were used 

 Teens to the 300 mgrs, of RaBr s . The position of the 

 electroscope was at right angles to the normal. 



From the tabic it is seen that the screen has a hardening 

 effect. Similarly it was shown that any other screen always 

 had a hardening effect. The ratio of the absorption coefficients 

 remains the same For each radiator, and the results go to 

 show that this ratio keeps constant for each position of the 

 electroscope. 



Lead has always been used as the absorbing screen in these 

 experiments, as the changes in coefficient of absorption are 

 much more marked than with any of the lighter substances. 

 x . i : similar results are given for screens of iron or zinc. It 

 is well known that lead will cut out the sofl radiation to a 

 much greater extent than iron. Tins holds tor the secondary 

 y-vn\> as well as for the primary. 



Radiator, 



175 cm. of l'b. 



10 cm. of C 



2-5 cm. of Pb 



A Ph = --lG 



„. I! 



1 1 \5 cm. of Fe. '875 cm. of Pb. 

 ■V. ="28 



■24 



Direct Radiation. 



Tb 



1-CO 



105 cm. of Fe. 



■56 



X Fe ='49 



lileotroacope turned through 90°. 



The absorption coefficient is first determined for *875 cm. 

 of lead, then for 1*05 cm. of iron. Hence, while the absorp- 

 tion coefficient of the radiation changes from '70 to 2'iJS 

 when measured by '875 cm. of lead, it only changes from 

 "2$ to "56 in the case of iron. Carbon shows this effect to a 

 less extenl than iron. 



All metals will send out a radiation of the same quality 

 provided the right thickness of radiator is used. 



Incident secondary y-rays. 



A few experiments were carried out on the radiation 

 emitted from the surface of the plate against which the 

 primary rays strike. This radiation from iron and lead was 

 softer than the emergent secondary radiation. This suggests 

 that the softest radiation is most scattered. This incident 

 radiation is similar in type to the emergent secondary and to 

 the primary radiation. 



