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XXXIX. Secondary 7 Radiation. By J. P. V. Madsen,. 



IJ.Sc. {Add.), B.E. {Syd.), Lecturer in Electrical En- 

 gineering, Unhersity of Adelaide *. 



[Plate VIII.] 



Inthoduction. 



AS a result of the passage of 7 rays through matter,. 

 secondary rays of two types make their appearance. 

 As it will be necessary to distinguish between the secondary 

 rays which proceed from the sides at which the original 7 

 rays enter and emerge from the plate which they penetrate, 

 we shall refer to these as the "incidence" and "emergence" 

 rays respectively. 



The secondary radiation consists of j3 and of 7 rays. 



The former appear on both sides of the plate ; the " inci- 

 dence " (3 rays have been recently investigated in some 

 detail by Kleeman (Phil. Mag., Nov. 1907) and by Eve 

 (Phil. Mag., June 1908). 



In papers bv Professor Bragg and myself (Phil. Mag., 

 May 1908 : Trans. Roy. Soc. S. Acis. vol. xxxii. 1908) it is 

 shown that most of the experimental results so far obtained 

 with these rays can be very simply explained on the " mate- 

 rial " theory, if we suppose that the /3 radiation is produced 

 directly from the 7 particle and at the outset moves in the 

 direction of the original 7 radiation, subsequently under- 

 going scattering in the ordinary manner of ft rays. 



The second type of secondary radiation resulting from 

 tiie primary 7 rays, viz., the secondary 7 rays, has been 

 investigated on the incidence side of plates of different 

 material by Kleeman (Phil. Mag., May 1908), and later by 

 Eve (Phil. Mag., Aug. 1908). 



It was a deduction made by Professor Bragg (Trans. Roy. 

 Soc. 8. Aus. Jan. 1908) from the theory of the material 

 nature of X and of 7 rays previously propounded by him, 

 that " the existence of modified or softened 7 rays might be 

 suspected, since there is an analogous effect in the case of 

 X-rays ; and probably they would be found more at the 

 back of the penetrated plate than in front of it." The back 

 and front sides spoken of here refer of course to the sides of 

 emergence and incidence respectively. 



* Communicated by the Author. From 'Transactions of the Royal 

 Society of South Australia, 1 vol. xxxii. 1908. Preliminary account 

 read Julv 17, 1908. 



