The disintegration of boron into three α-particles

Abstract The first experiments upon the disintegration of boron under proton bombardment were made by Cockcroft and Walton who reported the emission of α-particles of range about 3.5 cm. Their subsequent researches, together with those of Oliphant and Rutherford, and of Kirchner, proved that the products of this bombardment, unlike those of practically all other transmutation experiments, were not homogeneous in energy, but consisted of a continuous distribution of α-particles with a maximum range of 4.7 cm. The most natural assumption which could be made to interpret these results was that the boron nucleus disintegrated in the manner 115B + 11H → 42He + 42He + 42He (1) this transmutation differing from the usual type in that three instead of two particles were emitted. It was natural to anticipate that the detailed study of a nuclear disintegration into three particles would present great difficulties both in experimental investigation and in the theoretical interpretation of the results. A satisfactory value for the energy liberated in this process could not be derived from the experimental data until quite recently, while even the main features of the distribution of energy among the products have not yet been explained. For a long time the only satisfactory experimental evidence that the disintegration was in the manner postulated lay in the observed inhomogeneity of the products. Much of our work, therefore, has been to obtain direct verification of this hypothesis. The mechanism of disintegration of a nucleus into three particles is a problem of which practically nothing is known and it was hoped that a systematic study of the cloud track photographs of such a process might lead to interesting results.