[d ou glas] 



iS-RAYS FROM RADIUM 



117 



Table I shows the results obtained for (1) Absorption of primary 

 (8-rays; (2) absorption of /3-rays scattered from a lead radiator, 3 mm. 

 thick; (3) absorption of /3-rays scattered from a silver radiator, 0.3 

 mm. thick. The absorber in each case was paper, each sheet of which 

 weighed 0.00848 pms. per sq. cm. 



TABLE I 



In Fig. 4 are given the curves corresponding to (1) and (2) above 

 mentioned. 



These results point very definitely to the fact that the scattered 

 rays have a range only slightly less than that of the primary rays, 

 because it is certain that practically no primary rays go beyond 57 

 sheets, while in the case of the secondary rays it is certain that some do 

 pass 49 or 50 sheets. This represents at most only 10 per cent, or 

 12 per cent, loss of energy as a result of scattering, and for the following 

 reasons it will be shown that this is considered an upper limit, the 

 actual loss being probably very much less, if indeed it exist at all. 



(1) It should be noted that only a small proportion of the rays 

 emitted have a very high velocity and it is the effect of this small 

 proportion which has to be accurately measured as the range is 

 approached. From the table it will be seen that at 56 sheets the 

 intensity of the primary rays has been cut down to 1/500,000 of its 

 original value. The difficulty of measurement arising from this 

 reduction comes into play sooner in the case of scattered radiation 

 since the original intensity is much less, and the proportion of high 

 velocity rays is lower since they are less likely to bis deflected than the 



