COULOMB DISPLACEMENT ENERGIES FOR ZN-GA ISOBARS

Fast neutrons from (p, n) reactions due to 18 MeV protons incident on zinc targets are detected by means of the 28Si(n, α)25Mg reaction taking place in the volume of a 2 mm deep surface barrier-detector. Energy resolution for 8 to 12 MeV neutrons was observed to be 160 keV. Despite the difficulties of a continuous neutron background and the fact that (n, α) reactions in silicon can leave the 25Mg in many allowed excited states, it was possible to see isobaric analogs of the ground states of the zinc target nuclei in the gallium isotopes. By using the detector to measure the energy of neutrons corresponding to these states, Coulomb displacement energies for the ZnGa isobars are determined to be 9890, 9800, 9790, 9760 and 9620±50 keV for A = 64, 66, 67, 68 and 70, respectively. These result are consistent with the A- 1 3 dependence which is characteristic of other nuclei in this mass region. © 1969.