The Disintegration of Boron by Slow Neutrons

The total ionization produced by the ${\mathrm{Li}}^7$ and $\alpha$-particles from the ${\mathrm{B}}^{10}(n,\alpha ){\mathrm{Li}}^7$ reaction has been measured in an argon-boron trifluoride gas mixture, and that produced by the two particles separately with a thin boron film. Electron collection has been employed, using a fast amplifier feeding a 30-channel pulse-analyzer. The results indicate a departure from linearity in the relation between ionization and energy. Using the formula suggested by Cranshaw and Harvey in their work on natural $\alpha$-emitters, values of the $Q$ of the boron reaction have been obtained. They are 2.793±0.027 Mev and 2.320±0.020 Mev for the ground state and excited state transitions, in agreement with the recently published values of Tollestrup, Fowler, and Lauritsen. The branching ratio, that is the probability of the reaction going to the ground state, has been measured as 5.8±0.1 percent.