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LXXII. Recoil Atoms in Ionized Air. By Alois F. Kovarik, 

 Ph.D., Assistant Professor of Physics, University of 

 Minnesota *. 



WHEN a radioactive emanation disintegrates, the atom 

 o£ the newly formed substance may be drawn to a 

 negatively charged electrode. This was investigated by 

 Rutherford and others. Rutherford f also measured the 

 velocity in air of the atoms formed from radium emanation 

 and from thorium emanation, and found these to be the 

 same as the velocity of the positive ion in air. Schmidt { has 

 shown that the RaA atom behaves like a positive ion in air. 

 The recoil experiments of Halm and Meitner § show that the 

 atoms formed after the disintegration of other radioactive 

 substances are also drawn to the negative electrode in an 

 electric field. Franck || using the recoil atoms, thorium 1), 

 showed that their velocity in an electric field was the same 

 as that of the positive ion in the corresponding gas. It 

 therefore appears that the recoil atoms of all disintegrating 

 radioactive atoms behave like positive ions in the same gas. 

 A theory attempting to explain these results has been put 

 forth by Wellisch IT. 



The present experiments were undertaken principally to 

 ascertain if the recoil atoms could be collected on a negatively 

 charged electrode when the air between the plates of the field 

 was strongly ionized. From the experiments referred to 

 above, one would anticipate that the number of atoms drawn 

 to the negative electrode through ionized air would diminish 

 with the intensity of the ionization on account of the neutrali- 

 zation of the charge of the atoms with the negative ions of 

 the air. The results of these experiments confirm this idea. 

 Wellisch and Bronson**, however, in some of their recently 

 published experiments, come to the conclusion that the effect 

 of the Rontgen rays passing through a gas in which the recoil 

 atoms, Ra A, were collected was appreciable only when the 

 activity and ionization were far from saturation. 



An investigation was also made showing that the number 

 of recoil atoms drawn to the negative electrode increased as 

 the potential difference between the plates was increased, the 

 distance remaining constant ; and also, that the number 



* Communicated by Prof. E. Rutherford, F.R.S. 

 f Rutherford, Phil. Mag. v. p. 95 (1903). 

 J Schmidt, Phys. Zeit. ix. p. 184 (1908). 



§ Harm and Meitner, Verh. Jl Phys. Ges. xi. (3) p. 55 (1909). 

 || J. Franck, Verh. 1). Phys. Ges. xi. (19) p. 397 (1909). 

 «| Wellisch, Ver. I). Phys. Ges. xiii. p. 159 (1911). 

 ** Wellisch and Bronson, Phil. Mag. xxiii. p. 714 (1912). 



