The Disintegration of Nitrogen by Neutrons

Abstract

Measurements made on 29 Wilson cloud chamber photographs of the disintegration of nitrogen by artificially produced neutrons (beryllium+deutons) are presented and discussed. It is shown that the loss in kinetic energy can be satisfactorily accounted for by postulating the momentary production of a radioactive nitrogen ${\mathrm{N}}^{15}$ by a radiative capture of the neutron. This nitrogen disintegrates with the emission of $\ensuremath{\alpha}$-particles so that the half-life on the Gamow theory is around ${10}^{\ensuremath{-}20}$ sec. A distinction is thus made between nuclear transformations in which the energy absorbed is a constant (such as in the case of the disintegration of nitrogen by $\ensuremath{\alpha}$-particles) and those in which the proper disintegration energy $E$ is a constant. Disintegrations caused by neutrons are, as far as the data from cloud chamber measurements go, all of this latter type. For nitrogen $E$ is found to be 3.1 MV. The scatter of the values of $E$ is probably all to be attributed to experimental error but may in part be due to the short life of the radioactive ${\mathrm{N}}^{15}$. The energy level from which the $\ensuremath{\alpha}$-particle leaves the ${\mathrm{N}}^{15}$ nucleus is roughly identified with the resonance level through which an $\ensuremath{\alpha}$-particle may enter a ${\mathrm{B}}^{11}$ nucleus in the reverse reaction. A mass for the radioactive ${\mathrm{N}}^{15}$ of 15.0166 is proposed on the basis of the mechanism here discussed. The data of other workers on the transmutation of oxygen, fluorine and neon are reviewed in the light of these considerations and lend support to them. The values found for $E$ are nearly the same for all of the four elements on which data exist.

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