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Low-lying excited states of the neutron-rich calcium isotopes 48−52 Ca have been studied via γ-ray spectroscopy following inverse-kinematics proton scattering on a liquid hydrogen target using the GRETINA γ-ray tracking array. The energies and strengths of the octupole states in these isotopes are remarkably constant, indicating that these states are dominated by proton excitations.2

We have performed measurements of the 0 + g.s. → 2 + 1 excitations in the neutron-rich isotopes 48,50 Ca via inelastic proton scattering on a liquid hydrogen target, using the GRETINA γ -ray tracking array. A comparison of the present results with those from previous measurements of the lifetimes of the 2 + 1 states provides the ratio of the neutron and proton matrix elements for the 0 + g.s. → 2 + 1 transitions. These results allow the determination of the ratio of the proton and neutron effective charges to be used in shell model calculations of neutron-rich isotopes in the vicinity of 48 Ca.

In the original article we neglected to cite Ref. [1]. That reference had in fact already firmly established via high-resolution bunched-beam collinear laser spectroscopy the J π = 3/2 − value of the ground state of 51 Ca, which we had suggested. This omission does not change any of our conclusions regarding spins and parities of the states we observed in 51 Ca, and in fact strengthens them.

Excited states of the N = 32 nucleus 54 Ti have been studied, via both inverse-kinematics proton scattering and one-neutron knockout from 55 Ti by a liquid hydrogen target, using the GRETINA γ-ray tracking array. Inelastic proton-scattering cross sections and deformation lengths have been determined. A low-lying octupole state has been tentatively identified in 54 Ti for the first time. A comparison of (p, p ′ ) results on low-energy octupole states in the neutron-rich Ca and Ti isotopes with the results of Random Phase Approximation calculations demonstrates that the observed systematic behavior of these states is unexpected.

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The (γ, n) and (γ, p) cross sections in A40 have been measured as a function of photon energy from threshold to 24 Mev. The (γ, n) cross section was found to have a peak value of 38 mbarns at 20 Mev. and an integrated cross section of 0.35 Mev-barn. These values for the (γ, p) cross section were found to be 120 mbarns at > 25 Mev. and 0.54 Mev-barn respectively. In spite of the higher (γ, p) threshold, it was found that the two cross sections were equal at 19.5 Mev. and above this energy the (γ, p) cross section became larger. This interesting result is discussed.

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