a Part cles witJi Ligld Atoms. 539 



number of H scintillations from an a-ray tube immediately 

 alter it was tilled with emanation. It is well known that 

 the amount of radium C in such a tube increases at first very 

 slowly. For example, after filling a tube with emanation, 

 the fraction of the final amount of radium C present after 

 10 minutes is only. 2 per cent., but reaches 9 per cent, 

 after 20 minutes *. Consequently, observations made on 

 the number of scintillations within 10 minutes after filling 

 should decide definitely whether the scintillations arise from 

 radium C alone and not from the other a-ray products 

 present, viz. the emanation and radium A. In the latter 

 case, the number of scintillations after 10 minutes should be 

 only 2 per cent, of the final number reached about three 

 hours later when radium C is in transient equilibrium with 

 the emanation. 



A number of a-ray tubes were kindly made and filled for 

 me by Mr. X. Tunstall, B.Sc. The whole process of filling 

 and removal for testing was done as rapidly as possible, and 

 the counting of scintillations was usually begun within four 

 minutes after filling. The a-ray tube was placed between 

 the poles of a strong electromagnet in order to reduce the 

 luminosity due to j3 rays on the zinc sulphide screen, placed 

 2 centimetres beyond the range of the a rays. After every 

 precaution had been taken to avoid radioactive contami- 

 nation, the number of scintillations observed between 4 and 

 10 minutes was greatly in excess of the number to be 

 expected if they had their origin in the transformation of 

 radium alone. The actual ratio of the maximum number 

 varied with the thickness of the a-ray tube, hut the fraction 

 observed initially was from 20 to 40 per cent, of the maximum 

 reached three hours later. 



These results showed conclusively that, if the H atoms from 

 a glass a-ray tube were a product of radioactive disintegration, 

 they arose not only from radium C but also from radium A 

 or the emanation or both. It is hoped to discuss in a later 

 paper the results of a number of experiments to test whether 

 hydrogen is a product of radioactive change. It is not easy 

 to give a decisive answer to this important problem on 

 account of the numerous factors involved. It will be seen 

 later that the number of scintillations from hydrogen is 

 much greater than is to be expected on the simple theory, 

 and it is difficult to be sure of the absence of hydrogen as a 

 contamination in the source and absorbers of the radiation. 

 In addition, both nitrogen and oxygen atoms are set in such 

 swift motion by collision with a particles that they cause 



* ' Radioactive Substances and their Radiations,' Rutherford, p. 499. 



2 P 2 



