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LXXXIX. The Artificial Disintegration of Light Elements. 

 By Sir E. Rutherford, F.R.S., Cavendish Professor of 

 Experimental Physics, and J. Chadwick, Ph.D., Clerk 

 Maxwell Scholar, University of Cambridge *: 



IN previous papers, one f of us Las shown that when 

 swift a particles pass through dry air or nitrogen, 

 a few long-range particles are produced which can be 

 detected by their scintillations on a zinc-sulphide screen. 

 These particles were bent in a magnetic field to about the 

 same extent as swift H atoms of the same range, and it was 

 ^concluded that some of the nitrogen atoms were disintegrated 

 by the intense collisions with a. particles and that a positively 

 charged hydrogen atom (H atom) was liberated at a high 

 speed. No such long-range particles were observed in 

 oxygen or carbon dioxide. In these preliminary expe- 

 riments, the scintillations due to the H atoms were so 

 few in number and so feeble in intensity, that it was found 

 difficult to decide with certainty whether the maximum 

 range of the H atoms from nitrogen differed from that for 

 the corresponding H atoms set in swift motion by the 

 passage of » particles through hydrogen or other hydrogen 

 material . 



Recently the optical arrangements of the microscope have 

 been so improved that the counting of scintillations has 

 become much easier and more certain. By this means, it 

 was at once found that the particles from nitrogen had a 

 greater range of penetration than the corresponding H atoms 

 from hydrogen. For example, using radium G as a source 

 of ol rays with a range in air of 7 cm., no H atoms from 

 hydrogen can be detected after passing through absorbing 

 screens of aluminium or mica of stopping-power equivalent 

 to 29 cm. of air. On the other hand, the maximum range of 

 the particles from nitrogen corresponds to 40 cm. of air. 

 This shows at once that the emission of these particles from 

 nitrogen cannot possibly be ascribed to the presence of free 

 hydrogen or l^drogen in combination as a contamination. 

 This observation gave a simple method of testing whether 

 other elements besides nitrogen emitted long-range particles. 

 If the scintillations are counted for absorptions greater than 

 29 cm. of air, the results are quite independent of the 

 presence of hydrogen as an impurity in the substance under 



* Communicated b} r the Authors. 



t Rutherford, Phil. Mag-, xxxvii., I. II. & III., pp. 588 587 (1919) 5 

 Bakerian Lecture, Proc. Roy. Soc. A, xcvii. p. 374 (1920). 



Phil Mag. S. G. Vol. 42. No. 251. Sov. 1921. 3 II 



