The transmutation of heavy hydrogen investigated by the cloud-track method

One of the most important cases of artificial transmutation which have been investigated is that in which compounds containing heavy hydrogen arc bombarded with high velocity 1H2 ions. It was first shown by Oliphant, Harteck and Lord Rutherford that such bombardment resulted in a copious emission of two proton groups of ranges 15·0 cm and 16·0 mm the relative numbers of particles in the two groups being equal within the errors of measurement. They postulated as a mechanism for the process involved the reaction 1H2 + 1H2 → 1H1 + 1H3 (1) and showed that if one assumed the 1H1 particles to constitute the 15·0 cm group then the range of the 1H3 particles, calculated by the application of conservation of momentum to this process, was in approximate agreement with the shorter range. Expansion chamber photographs obtained by one of us showed that in this bombardment the particles of 15·0 cm and 16·0 mm range were emitted in pairs in opposite directions, this result providing strong evidence in favour of the proposed reaction. In addition to this proton emission, however, it was shown by Oliphant. Harteck and Lord Rutherford that an intense neutron emission resulted from this bombardment and from an expansion chamber investigation by one of us of helium nuclei recoiling from these neutrons it was shown that the neutrons were probably homogeneous and that their energy was 1·8 × 106 electron volts. An investigation by Oliphant, Harteck and Lord Rutherford using a linear counting chamber gave a maximum value for the neutron energy of about 2 × 106 electron volts. The reaction proposed by Oliphant, Harteck and Lord Rutherford to account for these neutrons was 1H2 + 1H2 → 0n1 + 2He3. (2) The mass of the 2He3 atom was obtained by them from the data for the disintegration of 3Li6 by protons. {3Li6 + 1H1 → 2He3 + 2He4}, and using the value thus derived (3·0166) and a neutron mass of 1·0067 they showed that the energy of the neutrons calculated from (2) was 2·5 × 106 electron volts in approximate agreement with the observed value. Attempts were made by counting methods to detect the 2He3 nuclei which are to be expected according to the above reaction but were unsuccessful. The range to be expected from the above data is only 5 mm and the detection of particles of so short a range is very difficult and could not be expected under their experimental conditions. We first tried to detect these particles by passing a beam of 1H2 ions into an expansion chamber on to a solid target of heavy ammonium sulphate, but this experiment also failed probably on account of exchange of the heavy hydrogen in the target with the hydrogen of the water used in the chamber.