A Precise Determination of the Energy Released in the Production of Deuterium from Beryllium under Proton Bombardment

The kinetic energy of the deuterons liberated in the reaction ${\mathrm{Be}}^9 \mathrm{}(p,d)\mathrm{} {\mathrm{Be}}^8$ has been measured by deflecting the deuterons in an accurately known electrostatic field. The technique of the use of the electrostatic deflector is discussed, and experimental arrangements appropriate to the determination are described. From measurements at proton energies of 258, 262, and 315 kv the energy released in the reaction is found to be 0.557±0.006 Mev. The shift of the high energy limit of the deuterons with bombarding voltage establishes the masses of the particles involved. By combining the result with other energy data as known at present it is shown that ($a$) the threshold for the disintegration of ${\mathrm{Be}}^9$ by gamma-rays is 1.62±0.02 Mev. ($b$) ${\mathrm{Be}}^8$ is stable with respect to disintegration into two alpha-particles by 0.174±0.09 Mev. Revision of the present values of the mass-spectrographic bracket between deuterium molecules and helium, or the value of the energy released in the reaction ${\mathrm{Li}}^6 (d,\alpha ) {\mathrm{He}}^4$ would necessitate revision of conclusion ($b$). The experimental evidence on the stability of ${\mathrm{Be}}^8$ is briefly discussed.