March 3, 1922] 



SCIENCE 



229 



This explanation, it will be noted, implicitly 

 assumes that positively charged bodies attract 

 one another at the very small distances involved 

 in the close collisions between alpha particles 

 and atomic nuclei. Rutherford and Chadwick 

 have pointed out that in order that the collid- 

 ing alpha particle may communicate much of 

 its momentum to an H particle satellite the 

 latter must be held by strong forces to the 

 nucleus. If, however, the H satellite is very 

 close to the nucleus the alpha particle may 

 have to communicate a considerable fraction of 

 its momentum to the central nucleus, and the 

 velocity of escape of the H satellite is cor- 

 respondingly reduced. This for example may 

 be the explanation why the . alpha particles 

 from aluminium are ejected at higher speeds 

 than those from phosphorus ■ of higher nuclear 

 charge. In phosphorus the H satellites may 

 move so close to the nucleus that the alpha 

 particle is able to give a sinaller share of its 

 momentum to the H satellite than in the case 

 of the more distant satellite of aluminium. 

 (e) Close satellites. 



So far no H particles have been obtained 

 with elements heavier than phosphorus. The 

 failure to obtain them with such elements may 

 be due to the fact that the H atoms either move 

 very close to the central nucleus or are incor- 

 porated in it. 



(/) Disruption potential. 

 The theory of nuclear disintegration put for- 

 ward would seem to demand a definite disrup- 

 tion potential for nuclei having one or more 

 H satellites revolving about them. The experi- 

 ments with aluminium support this view as 

 no H particles are released from aluminium 

 nuclei by a particles of range in air less than 

 5 cm. The disruption potential for the nuclei 

 of aluminium atoms, i. e., the potential differ- 

 ence required to communicate the same energy 

 to an electron as is possessed by the a particle 

 is of the order of six million volts. The cor- 

 responding potential to liberate an electron 

 from the K or inner ring of electrons^ of the 

 atoms of aluminium is only about 2,200 volts. 

 By a simple calculation it can be shown that 

 the results obtained by Rutherford indicate 

 that by operating at six million volts one could 

 with the daily expenditure of 600,000 H.P. 



disintegrate the nuclei of three cubic feet of 

 nitrogen and obtain thereby not only the re- 

 covery of the 600,000 H.P. but also approxi- 

 mately 80,000 H.P. in addition. 



(g) Atomic weight of nitrogen. 



If the view put forward is correct that the 

 H particles are satellites of the central or main 

 nucleus the mass of the H satellite, — since it is 

 not in the "closely packed" condition, — should 

 not be very different from that of a free H 

 nucleus. Assuming that the nitrogen nucleus 

 is derived from that of carbon by the addition 

 of two H satellites and one electron, one might 

 expect the atomic weight of nitrogen to be 

 14.016, assuming C = 12.00, and H = 1.008 

 in terms of = 16. By a slight refinement of 

 Aston's positive ray analysis it should be pos- 

 sible to examine this point. 



(h) Atomic energy. 



A matter of primary importance which has 

 emerged from the experiments on the disinte- 

 gration of atomic nuclei is that the energy of 

 the H particle as it is ejected from aluminium 

 atoms by the impact of a particles is 1.40 

 times the energy of the impinging a particles. 

 Even when ejected in a backward direction the 

 released H particle has kinetic energy about 13 

 per cent, greater than that of the a particle, 

 causing its ejection. This additional energy 

 must come from the atom in consequence of its 

 disintegration. We have therefore in these 

 experiments of Rutherford strong indications 

 of a method of attack which, if followed up, 

 may open a way to the release of the stores 

 of atomic energy existing in ordinary materials 

 about us. 



(1) H, particles. 



In addition to the long range H particles 

 liberated from nitrogen, the passage of a. par- 

 ticles through oxygen as well as through nitro- 

 gen gives rise to much more numerous swift 

 atoms which have a range in air of about 9 

 cms compared with that of 7.0 cm. for the col- 

 liding a. particles. From preliminary observa- 

 tions on these particles they appear to have a 

 -mass of 3 and to carry a positive charge 2e. 

 They would thus seem to be the nuclei of an 

 isotope of helium. A number of experiments 

 have been made by Rutherford with a particles 

 traversing gases other than oxygen and nitro- 



