Decembee 26, 1919] 



SCIENCE 



583 



hydrogen rays. His experiments furnish con- 

 clusive evidence that hy this bombardment, 

 nitrogen atoms may be disrupted and thus 

 transformed or transmuted. 

 ' In the paper preceding the one just men- 

 tioned, Rutherford describes other secondary 

 rays produced by alpha ray bombardment in 

 both nitrogen and oxygen, which have a range 

 in air of 9 cm. instead of 28 cm. These rays, 

 he states, are presumably swift, singly charged 

 nitrogen and oxygen atoms, respectively. The 

 purpose of this note is merely to point out that 

 their nature may be more interesting than their 

 discoverer suggests. 



The conclusion that they may be singly 

 charged atomic rays is based on the fact that 

 the computed ranges for such rays, 9.3 cm. 

 the same as the observed ranges, 9 cm. in each 

 case, whereas doubly charged atomic rays 

 would be expected to have only one fourth 

 these ranges. But the agreement is not very 

 convincing, and there are other reasons for 

 doubting the correctness of the hypothesis. 



The alpha-ray experiments practically force 

 us to accept the nuclear atom. In the case of 

 such an atom, is it possible that a singly 

 charged nitrogen ray may be produced as a re- 

 sult of a close collision between an alpha ray 

 and a nitrogen nucleus? I think not; for 

 since a singly charged nitrogen atom is a nu- 

 cleus with six orbit electrons attached, a singly 

 charged nitrogen ray could be produced only 

 if each of the electrons as well as the nucleus 

 were acted upon by the relatively large force 

 required to give it a speed of aibout 10° om./sec. 

 in less than 10"'* sec. It can easily be com- 

 puted that the field of the nucleus is insuffi- 

 cient to hold the electrons under these circum- 

 stances. Therefore, unless we postulate a 

 stability which ionization phenomena seem to 

 disprove, we must conclude that after such col- 

 lisions, the orbit electrons are left behind. 

 Moreover, even if singly charged rays were 

 shot out, it is difficult to believe that most of 

 the orbit electrons would not soon be detached 

 as a result of the passage of the rays through 

 many atoms. In other words, various experi- 

 ments have given us a conception of the struc- 

 ture of atoms which makes it highly improb- 



able that singly charged nitrogen rays would 

 be produced as a result of bombardment by 

 alpha rays. 



Now the secondary nitrogen rays can not be 

 multiply charged nitrogen atoms or nuclei, for 

 such rays would have too short a range. And 

 they can not be hydrogen rays because the 

 scintillations they produce are too bright. 

 Therefore they must be fragments of nitrogen 

 nuclei which are larger than hydrogen nuclei. 

 Rutherford has proved, as stated above, that 

 nitrogen nuclei can be disrupted by alpha rays. 

 If we suppose, as seems probable, that the ni- 

 trogen nucleus is made up of hydrogen and 

 helium nuclei, then the disruption of the nu- 

 cleus would be expected to result in both hy- 

 drogen and helium rays. It is therefore pos-- 

 sible that the less penetrating secondary rays 

 ohserved hy Rutherford when nitrogen is 

 homiarded are alpha rays produced by the dis- 

 ruption of nitrogen nuclei. The similar rays 

 observed with oxygen may also be secondary 

 alpha rays originating in disrupted oxygen 

 nuclei. The fact that the scintillations pro- 

 duced by these rays are much like those due to 

 alpha rays of the same range supports this 

 suggestion. 



. But how is it possible for the range of the 

 secondary alpha rays to be greater than that of 

 the primary rays, in violation of the laws of 

 mechanics? Just as the energy of alpha rays 

 comes from the jwtential energy released when 

 a radioactive atom becomes unstaible, so the 

 rays resulting from the disruption of a nitro- 

 gen nucleus may be expected to receive energy 

 as a result of the mutual repulsion of the frag- 

 ments. If the secondary rays are alpha rays, 

 then, the effect of the bombarding alpha rays 

 must be to make the nuclei unstable, produc- 

 ing an artificial radioactivity. 



It is believed that the difficulty of explain- 

 ing why so many of the secondary rays travel 

 in the direction of the bombarding rays is no 

 greater from this point of view than from the 

 other. 



It will be extremely interesting to determine 

 by deflection methods the mass and charge of 

 these rays so as to decide whether they are in 

 fact nuclear fragments. In this way we may 



