184 Prof. A. Stanley Mackenzie on Secondary Radiation 



From this we see that the ft rays cease increasing their 

 effect after a thickness of lead of about £ mm. is reached. 

 But for the 7 rays it requires more than 6 or 7 mm. before 

 the limit is reached. An important conclusion from this is 

 that some of the secondary rays from lead produced by 7 rays 

 passing into it are of a highly penetrating character and can 

 return through 6 or 7 mm. of lead. Moreover, we saw before 

 from Table II. that the 7 rays produce comparatively little 

 absorbable radiation as compared with that from the ft rays : 

 so that it seems that a large part of secondary radiation is 

 always of a similar type to the primary. Curves A and B 

 of fig. 2 show the growth of the secondary radiation with 









Fig- 



2. 













1 



1 A 











X 



/ 



^ 



1 

 1 











i 

















\\ \ 







B 

















D 











I 



















^*s 



■^■^ 



— _C___ 

















A. Reflected radiation from j3 ravs. Unit absc. = '5 mm. 



Unit ord. = leak of 100. 



B. Reflected radiation from y rays. Unit absc. = 5 mm. 



Unit ord.= leak of 5. 



C. Transmitted radiation from /3 rays. Unit. absc. = "5 mm. 



Unit ord. =leak of 50. 

 — D. Transmitted-radiation from y rays. Unit absc. = 5 mm. 

 Unit ord. = leak of 5. 



thickness for the ft and 7 rays respectively. They are drawn 

 to different scales, but it will be seen that they follow the 

 same general law. They suggest the equation y = a(l — e~ M ) y 

 but the rise is too steep and they flatten too quickly after 

 passing the knee. 



