Coulomb Displacement Energies Derived from thep,nIsobaric Reaction

Abstract

The agreement of Coulomb displacement energies derived from the nonmirror ($p,n$) isobaric reaction with those obtained from mirror and nonmirror ($T=1$) nuclei beta decay has been previously demonstrated. Using the Livermore 90-in. cyclotron time-of-flight facility, we have measured additional Coulomb displacement energies in the mass region $70\ensuremath{\le}A\ensuremath{\le}108$. These measurements indicate possible shell effects which were previously not observed because of the paucity of data. With the availability of 20.5-MeV protons, Coulomb displacement energy measurements were extended to the mass region $A\ensuremath{\le}165$. Even for nuclei as heavy as ${\mathrm{Ho}}^{165}$, where the Coulomb displacement energy is 16.6 MeV, the width of the isobaric neutron group was not measurable (\ensuremath{\le}150 keV). The variation of the uniform radius parameter with atomic weight ($A$) inferred from these data is compared with that obtained from high-energy electron scattering experiments and is found to be in substantial agreement. A semiempirical formula for calculating Coulomb displacement energies is presented.