Slow Neutron Disintegration ofB10andLi6

The disintegration of ${\mathrm{B}}^{10}$ by slow neutrons is found to result in two groups of alpha-particles, of ranges 0.80±0.03 and 0.66±0.05 cm and with relative intensities 1: 3, corresponding to disintegration into the ground state of the ${\mathrm{Li}}^7$ product nucleus and the 0.44 Mev excited state, respectively. The reaction energies obtained from these ranges with the best available range energy relation check well with those computed from atomic masses if a mass of ${\mathrm{B}}^{10}$ is used which is consistent with other nuclear disintegrations. The slow neutron disintegration of ${\mathrm{Li}}^6$ results in ${\mathrm{H}}^3$ particles of 5.90±0.06 cm range, indicating a reaction energy of 4.86 Mev. This is in disagreement with the value obtained from atomic masses and suggests errors in the mass values or the proton range energy relation. Techniques for the measurement of very short particle ranges are described, including methods for the determination of the depth of penetration into the recording ionization chamber.