Scattering of a and /3 Particles by Matter. 



685 



increase of t. Crowther, using aluminium as scattering 

 material, states that the variation of I/I was in good accord 

 with this theory for small values of t. On the other hand, 

 if single scattering be present, as it undoubtedly is for a rays, 

 the curve showing the relation between I/I and t should be 

 nearly linear in the initial stages. The experiments of 

 Madsen * on scattering of /3 rays, although not made with 

 quite so small a thickness of aluminium as that used by 

 Crowther, certainly support such a conclusion. Considering 

 the importance of the point at issue, further experiments on 

 this question are desirable. 



From the table given by Crowther of the value (pj V ' t m for 

 different elements for /3 ravs of velocity 2'68 X 10 10 cms. 

 per second, the values of the central charge N# can be 

 calculated on the theory of single scattering. It is supposed, 

 as in the case of the u rays v that for the given value of 

 <£/ \/ t m the fraction of the /3 particles deflected by single 

 scattering through an angle greater than dj> is *46 instead 

 of -5. 



The values of N calculated from Crowther's data are 

 given below. 



Element. 



Atomic 

 weight. 



0/ V tm. 



N. 



Aluminium 



27 



632 

 108 

 194 



4-25 

 10-0 

 154 

 29 



22 



42 



78 



138 



i 



Copper 



Silver 



Platinum 





It will be remembered that the values of N for gold 

 deduced from scattering of the a rays were in two calcula- 

 tions 97 and 114. These numbers are somewhat smaller 

 than the values given above for platinum (viz. 138), whose 

 atomic weight is not very different from gold. Taking into 

 account the uncertainties involved in the calculation from 

 the experimental data, the agreement is sufficiently close to 

 indicate that the same general laws of scattering hold for the 

 u and /3 particles, notwithstanding the wide differences in 

 the relative velocity and mass of these particles. 



As in the case of the a rays, the value of N should be 

 most simply determined for any given element by measuring 



* Phil. Mag. xviii. p. 909 (1909). 



