The Disintegration of the Nuclei of Nitrogen and Other Light Atoms by Neutrons. I

Disintegration experiments with N, C and Ne.---Thirtyone disintegrations of nitrogen have been found in 7600 pairs of photographs of a Wilson chamber through which neutrons were shot from a Be-Ms Th source. Of these, nineteen were disintegrations in which the neutron was captured according to the reaction N₀¹⁴+n₁¹→N₁¹⁵→B₁¹¹+He₀⁴. The distribution curve which shows the number of disintegrations for each velocity interval of the neutrons at capture exhibits a peak at 3.2×{}10⁹ cm/sec. The lowest velocity which produces such a disintegration is 1.9×{}10⁹ and the highest 5.5×{}10⁹. The form of the curve is explained by the assumption that the probability that a neutron will be effective in producing disintegration increases rapidly with its velocity but that, as the velocity considered lies higher and higher above 3.2×{}10⁹ cm/sec., the number of neutrons present at such a velocity decreases rapidly. The data are too few to show any indication of resonance. The highest energy found for a neutron at capture is 15.8×{}10⁶ electron-volts, while, according to theory, it should be 14.7×{}10⁶ provided the α-particle comes from Th C'.Disappearance of energy and emission of γ-rays.---Without exception, for every disintegration of an atomic nucleus by capture of a neutron, kinetic energy (a) has been conserved or (b), much more often, disappears. It is assumed that this energy plus any energy in the form of mass which disappears, is converted into γ-rays. The values obtained suggest that the spectrum of these γ-rays is a line spectrum, which obviously may be superimposed upon a continuous spectrum. Conclusive evidence of this cannot be obtained until the accuracy of the work is increased by an increase in the range of the disintegration products.Disintegration as related to scattering.---Nine disintegrations of the nitrogen nucleus were obtained in which it is probable that either (a) the neutron was first deflected by a nucleus and later disintegrated a nitrogen nucleus with capture or (b) the neutron was not captured.Modified Wilson cloud track apparatus.---The features of a modified Wilson apparatus, which are considered essential to the accuracy of this work, are described.Disintegrations of neon and carbon.---On June 12 thirteen disintegrations of neon nuclei were found in 3200 pairs of photographs. The kinetic energy which disappeared was found to vary from 5 to nearly 11 million electronvolts. The same number of photographs gave only 2 disintegrations in ethylene. Presumably these were disintegrations of carbon nuclei but it is possible that they were due to the oxygen of the water.