Coulomb displacement energies for 1f-2p shell nuclei

Abstract

Coulomb displacement energies for 29 stable isotopes between A = 42 and A = 70 have been measured to an accuracy of ±6 keV using the ( 3He, t) reaction at 24.6 MeV incident 3He energy. Coulomb energy shifts between members of an isotopic sequence have been determined to an accuracy of ±3 keV. Triton spectra were obtained at 18° using a calibrated position-sensitive detector in the focal plane of an Enge split-pole magnetic spectrometer. In most of the spectra a single, strong transition could be identified as the transition to the isobaric analogue of the target nucleus ground state and an unambiguous Coulomb displacement energy was calculated from the measured Q-value. The triton spectra for the residual nuclei 56Co, 58Co and 64Cu showed two strong transitions in the energy region expected for the analogue state. In these nuclei, the ( 3He, t) cross sections to any single state were lower than those expected from the systematics obtained from neighbouring isotopes. This indicates a fragmentation of the analogue strength. Off-diagonal Coulomb matrix elements in the range 5 to 35 keV can account for the observed energy splittings and ( 3He, t) cross-section ratios. The experimental Coulomb displacement energies were analysed using various models. The experimental isotopic shifts in Coulomb displacement energies were used together with measured shifts in charge radii to extract isotopic shifts in the radii of the neutron excess distribution.