494 Professor Sir Ernest Rutherford [June 4, 



WEEKLY EVENING MEETING, 



Friday, June 4, 1915. 



Charles Hawksley, Esq., M.Inst.C.E., Vice-President, 

 in the Chair. 



Professor Sir- Ernest Rutherford, LL.D. D.Sc. F.R.S. M.R.T. 

 (Nobel liaureate). 



Radiations from Exploding Atoms. 



It is now well established that the radio-active substances are under- 

 going spontaneous transformation, and that their characteristic 

 radiations— the a, y8, and y rays— accompany the actual disintegra- 

 tion of the atoms. The transformation of each atom results from 

 an atomic explosion of an exceedingly violent character, and in 

 general results in a liberation of energy many million times greater 

 than from an equal mass of matter in tlie most vigorous chemical 

 reaction. 



In the majority of cases the atomic explosion is accompanied by 

 the expulsion of an actual atom of matter— an a particle — with a 

 very high speed. It is known that the a particle is an atom of 

 helium which carries two unit positive charges, and which leaves the 

 atom with a velocity of about 10,000 miles per second. In some 

 transformations no a particle is ejected, but its place is taken by a 

 swift /? particle or electron. These p rays carry with them a large 

 amount of energy, for in some cases they are expelled very close to 

 the velocity of light, which is the limiting velocity possible for such 

 particles. The expulsion of high-speed /? particles is usually accom- 

 panied by the appearance of y rays, which correspond to X-rays, 

 only of greater penetrating power than has so far been obtained 

 from an X-ray tube even when a high voltage is employed. The 

 emission of energy in the form of y rays is not negligible, for in 

 some cases it is even greater than the energy emitted in the form 

 of high-speed /3 particles, and may amount per atom to as much as 

 20 per cent, of the energy released in the form of a swift a particle. 



By the application of a high voltage to a vacuum tube it is 

 quite possible to produce types of radiation analogous to those 

 spontaneously arising from radium. For example, if helium were 

 one of the residual gases in the tube, some of its atoms would 

 become charged, and would be set into swift motion in the strong 



