230 



Sf'lEiVCE 



[Vol. L^', Xo. 1418 



gen with tlie ol)jeet of defliiitely establishing 

 the origin of IJiese particles. The imperfec- 

 tion of metal foils, used in the experiments, 

 from the point of view of a rays is very great 

 and as yet no very final conclusions can be 

 drawn from the observations. So far, there is 

 always the possibility that these particles may 

 come from the source of a rays. The H, par- 

 ticles obtained from nitrogen are from five to 

 ten times as numei'ous as the H particles so 

 that if +hese particles really originate in the 

 nuclei of nitrogen atoms, it is clear that the 

 nitrogen nuclei can be disintegrated in two 

 ways and that the two forms of disintegration 

 must be independent and not simultaneous. 

 Since the H., and a particles both carry the 

 positive charge 2e, and the range of the former 

 is 27 per cent, greater than that of the latter, 

 it can easily be shown that the H„ particles 

 have a velocity 20 per cent, greater than that 

 of the a particles. The kinetic energy of the 

 Hg particles must therefore be about 8 per 

 cent, greater than that of the 7 cm. range a 

 particles. If, therefore, the H, particles are 

 ejected from nitrogen nuclei by the a jsarticles 

 there must be a gain of 8 per cent, in energy 

 of motion even though we disregard the suIj- 

 sequent motion of the disintegrated nucleus 

 and of the colliding a particle. It will be 

 interesting to follow developments in connec- 

 tion with these H., particles. If their existence 

 be confirmed by future experiments and it can 

 be shown definitely that they originate in the 

 nuclei of atoms of such elements as oxygen 

 and nitrogen, then we shall have in their pro- 

 duction a second example of the release of 

 atomic energy through the agency of a rays. 



(j) Alpha particles. 



Attention should he drawn to the branched 

 X-ray cloud tracks recently obtained by Takeo 

 Shimizu^^ by the vise of C. T. R. Wilson's 

 beautiful method of making visible the tracks 

 of ionising rays in gases. According to Ruth- 

 erford if about one hundred thousand a rays 

 from Radium C pass through air, on an aver- 

 age there will Ije one close nuclear collision 

 which results in the ejection of a swiftly mov- 



31 Shimizu, Proe. Eoy. Soe., Series A, Vol. 99, 

 pp. 425 aud 432, Aug., 1921. 



ing H particle. In Shimizu's experiments he 

 found that aljout one in every three hundred 

 a rays traversing air produce a branched track. 

 These branched tracks cannot therefore have 

 been produced by the ejection of an H particle. 

 One striking feature of the Shimizu branched 

 traelvs is that their shapes and sizes are very 

 similar aud the lengths of the two limbs of the 

 branches are approximately the same. The 

 angle between the two branches seems to vary 

 but little and judging from the photographs, 

 an example of which taken from Shimizu's 

 paper is shown in Fig. 2, it appears to be 

 aljout equal to a right angle. With these 

 In'anclied tracks the branching always takes 

 place near the end of the path of the a particle. 



Fig. 2 

 Pliotograpli of a branched a-ray track viewed 

 from two positions at right angles to each other. 

 Actual magnification 5.5. 



In this regard they differ from the short- 

 spurred tracks obtained by C. T. R. Wilson''- 

 where the alirupt bending of the a ray track 

 took place at different distances from the 

 source of the a particles. In Wilson's experi- 

 ments the angle between the direction of the 

 short spur and that of the deflected a particle 



3^ C. T. K. Wilson, Proe. Eoy. Soc, A, Vol. 87, 

 1912. 



