[RUTHERFORD] PROPERTIES OF THE a RAYS FROM RADIU.AI IB 



explanation. The action of the a rays in proJucing photographic 

 and phosphorescent action is primarily a result of ionization. This 

 ionization may possibly give rise to secondary actions which influence 

 the effects observed. 



This point of view is of interest in connection with the origin of 

 the "scintillations " observed in zinc sulphide and other substances when 

 exposed to the action of the oc rays. This effect is ascribed by 

 Becquerel to the cleavage of the crystals under the bombardment of the 

 a particles. Tnese results, however, show that we must look deeper 

 for the explanation of this phenomenon. The effect is primarily due 

 to the production of ions in the phosphorescent material and not to 

 direct bombardment, for we have seen that the a particle produces no 

 scintillations when it still possesses a large amount of kinetic energy. 

 It seems not unlikely that the scintillations produced by the a rays 

 must be ascribed to the recombination of the ions which are produced 

 by the a particle in the crystalline mass. It is difficult to see how this 

 ionization could residt in a cleavage of the crystals. 



This close connection of the photographic and phosphorescent 

 actions of the a rays with their property of producing ions raises the 

 question, whether photographic and phosphorescent actions in general 

 may not, in the first place, be due to a production of ions in the 

 substance. 



Bayless Changes. 



The results already discussed show that the a particles from the 

 radioactive substances are projected with an average velocity not more 

 than 30 per cent greater than the critical velocity below which the a 

 particles are unable to produce any ionizing, photographic or phos- 

 phorescent action. Such a conclusion suggests that the property of 

 the radioactive substances of emitting rays has been primarily defected 

 in thesç substances, because the a particles were projected slightly 

 above this critical velocity. A similar disintegration of matter may be 

 taking place in other substances at a rate much greater than in uranium 

 without producing much electrical effect, provided the a particles are 

 projected below the critical velocity. 



The particle, on an average, produces about 100,000 ions in the gas 

 before it is absorbed, so that the electrical effects observed are about 

 100,000 times as great as those due to the charge carried by the a 

 particles alone when the velocity falls below the minimum value. 



It is not imlikely that the numerous rayless products which have 

 been observed may undergo disintegration of a similar character to the 



