by u Particles from Radium Emanation. 913 



To render the results as accurate as possible, a large number 

 of experiments were made for the same target and the same 

 thickness of absorption material, and the mean value taken. 

 Also, since the first reliable readings in each experiment 

 could not be taken at times much less than 30 sees, from 

 zero, the process of extrapolating the curve to zero is open 

 to some objection on the grounds of personal error. Also 

 even at 30 sees, from zero the products radium B and 

 radium Q, which emit primary 7 radiation, are present in 

 minute quantity, and although their effect is small compared 

 with the initial activity observed, their presence has some 

 influence on the shape of the curve at the initial stages. 

 However, the flattening of the rise curve in its initial 

 stages is so marked and so invariable, that with some 

 certainty the radiation may be attributed to the a particles 

 from the emanation. 



Discussion of Radiation, 



The origin of this hard 7 radiation which is emitted when 

 the a. particles bombard metals such as lead and tin is 

 difficult to ascertain, with the meagre evidence at our disposal 

 concerning the mechanism by which the hard 7 radiations 

 emitted by many radioactive elements are excited. The radia- 

 tion under investigation differs but little in quality when the 

 radiator is changed from lead of high atomic number to tin 

 of medium atomic number. It is slightly harder for lead 

 than tin, and the intensity is about 50 per cent, greater for 

 the former than the latter under the same absorption con- 

 ditions. There seems to be little doubt, from the character 

 of these experiments, that the radiation is produced by the 

 a particles from radium emanation impinging on matter. 

 On any theory existing at present, the possibility of such a 

 hard radiation being generated by such collisions is highly 

 improbable. 



There is the question of the nucleus of the atom emitting 

 radiation after a close collision with an a particle. Some 

 evidence can be obtained from the results of these expe- 

 riments, indicating that this is a distinct possibility, in the 

 following way. The number of radium C atoms disinte- 

 grating per second at the equilibrium value is approximately 

 equal to the number of radium emanation atoms disinte- 

 grating per second initially — i. e., at the moment when the 

 emanation is admitted to the examination-tube. When it is 

 assumed that each radium C atom disintegrating emits 0110 

 7-ray, if such an expression may be used, and that one close 

 collision of the a particle with a lead nucleus emits one 7-ray 



