THE Scattering of the fi Rays of Radium. 



By J. P. V. Madsen, D.Sc. (Adel.), B.E. (Syd.), Lecturer 

 in Electrical Engineering, University of Adelaide. 



Preliminary Account read before the Australasian Associa- 

 tion for Advancement of Science, Brisbane, January 

 13, 1909. 



[Read April 6, 1909.] 



Introductory. 



In a paper by the author upon the secondary y rays (i) 

 it was shown that in passing through matter the y rays were 

 scattered and softened. The scattered radiation showed a 

 distinct lack of symmetry about a plane perpendicular to the 

 direction of the original stream, more scattered radiation 

 moving on in the direction of the original stream than was 

 turned back. The distribution of the scattered radiation was 

 found to depend upon the quality of the incident radiation 

 and also upon the nature of the medium in which the scat- 

 tering occurred. 



As the results arrived at in that investigation were used 

 as an argument in support of the material theory of y rays 

 proposed by Professor Bragg, and as J. A. Crowther (2) has 

 recently shown that the ;8 rays are subject to scattering by 

 even very thin layers of material, it became of special in- 

 terest to see whether any parallel could be drawn between 

 the effects of scattering in the case of the material jS par- 

 ticles and the y rays. 



It will be seen from the present paper that the parallel 

 is very close in many respects, the differences being such as 

 might reasonably be expected on the theory that the y ray 

 is a neutral pair. 



At the same time it is hoped that some of the . results 

 to be described may help to clear up some of the difficulties 

 which have arisen in the study of the absorption of )8 rays. 



(1) Trans. Roy. Soc, S.A., vol. xxxii. (1908). 

 (2' Proc. Roy. Soc, Sec. A., vol. Ixxx. (1908). 



A 



