Mr Crowther, On the Scattering of jB-rays, etc. 



273 



On the Scattering of the ^-rays from Radium hy Air. (Pre- 

 liminary Note.) By J. A. Crowther, M.A., St John's College. 



[Received 18 August 1909.] 



In a previous paper* I have described some experiments on 

 the scattering of a beam of the ;8-rays from Uranium by thin 

 sheets of various solid substances. It was shewn that a very 

 thin sheet of metal was sufficient to produce almost complete 

 scattering in a narrow pencil of /3-rays ; and further that the 

 diminution in intensity of a definite pencil of rays due to 

 the scattering of the rays, might be expressed by an exponential 

 law. 



The present paper contains a brief preliminary account of 

 some experiments, still in progress, on the scattering of a beam 

 of /3-rays from Radium during its passage through Air. 



A pencil of y8-rays from Radium is spread out into a magnetic 

 spectrum, a portion of which, consisting of rays having a definite 

 small range of velocities, falls on a small aperture in a lead 

 screen. The rays passing through this aperture are further 

 limited by a second screen, so as to form a narrow divergent 

 pencil of small angle consisting of rays of very nearly the 

 same velocity. The intensity of the /3-radiation passing through 

 the geometrical cross-section of this pencil, at various distances 

 from the origin, is measured by the ionization produced in an 

 ionization chamber. It has been found that if /„ is the initial 

 intensity of the pencil of /3-rays, and I the intensity passing 

 through the geometrical cross-section of the beam at a distance d 

 from the origin, then 



where cr is a constant, which may be called the coefficient of 

 scattering. 



The following table gives the values of a for ordinary air 



* Proc. Roy. Soc. A, Vol. 80, p. 186. 1908. 



