922 Excitation ofy Radiation hy « Particles from Radium. 



Summary. 



Part I — A hard 7 radiation is emitted when the a particles 

 from radium emanation impinge on metals like lead 

 and tin. 



The radiation differs but little in quality when the radiator 

 is changed from one o£ high atomic number to one of 

 medium atomic number. The coefficients of absorption in 

 lead are 1*8 cm. -1 for lead and 2*1 cm. -1 for tin. 



The intensity obtained is very small, and only a small 

 fraction of the impinging a particles can be effective. For 

 the same absorption conditions the intensity is about 50 per 

 cent, greater for the lead radiation than for the tin radiation. 



It appears to be emitted fairly uniformly in all directions, 

 but differs in all other respects from the characteristic 

 radiations. 



It is probably emitted from the nuclei of the atoms in the 

 radiator after direct collision with the « particles. 



No hard radiation is emitted by the disintegration of the 

 radium emanation nucleus in the ordinary course of radio- 

 active transformation. 



Part II. — Elements of high atomic number, when bom- 

 barded by « particles, emit two well-defined types of 

 radiation, corresponding roughly with their characteristic 

 " K " and " L " radiations. 



Tin, an element of medium atomic number, emits one type 

 (within the experimental range) of quality roughly the same 

 as its " L " radiation. 



The quantity of radiation emitted by any element is so 

 small that a very small fraction of the impinging « particles 

 can cause excitation. 



Radium emanation emits no soft radiation (within experi- 

 mental limits) on disintegration. 



Table III. 



Coeffs. are for [ijp in Aluminium, except where otherwise 



stated. 



Lead. Gold. 



Platinum. Tin. 



130 21-0 

 0-22 0-25 



, ,. .... | 



13-40 T85 

 0-32 



016 

 {fijp in Lead) 



— 



0-18 

 (/z/jO in Lead) 



