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THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



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[SIXTH SERIES] ^ ^ 







OCTOBER 191V* 



XLIII. The Origin of ft and 7 i2a#s /ro??i JRadioMbj&ti&fi- 

 stances. By E. Rutherford, F.R.S., Professor of Physics 

 the University of Manchester* . 



in 



FROM a study of the a radiations from active matter, it 

 has been found that each atom of a substance in dis- 

 integrating emits one a particle which is expelled with a 

 definite velocity and with a range in air characteristic of 

 that substance. The only exception is the product thorium 0, 

 which emits two distinct groups of a rays, each of definite 

 but different range in air. In this case, the atom appears to 

 break up in two distinct ways. 



In many transformations ft and 7 rays are emitted, and, 

 from analogy with the a ray transformations, it would be 

 expected that one ft particle of definite speed would be 

 emitted for the disintegration of each atom. The experiments, 

 however, of v. Baeyer, Hahn and Miss Meitner f , and later 

 of Danysz J, have shown that the emission of ft rays from a 

 radioactive substance is in most cases a very complicated 

 phenomenon. The complexity of the radiation is most simply 

 shown by observing the deflexion of a narrow pencil of 

 ft rays by a magnetic field in a vacuum. If the rays fall on 



* Communicated by the Author. A preliminary paper on this subject 

 was read before the Manchester Literary and Philosophical Society, 

 1912. 



t v. Baeyer and Hahn, Phys. Znt. xi. p. 488 (1910) ; v. Baeyer, Hahn 

 and Meitner, Phys. Zeit. xii. pp. 273, 378 (1911) ; xiii. p. 264 (1912). 



J Danysz, C. R. cliii. pp. 339, 1066 (1911; ; Le Radium, ix.p. 1 (1912). 



Phil Mag. S. 6. Vol. 24. No. 142. Oct. 1912. 2 H 



