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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.

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