The large double-focusing mass spectrometer recently constructed at this laboratory has been used to measure the atomic masses of the stable isotopes of iron, cobalt, nickel, copper, and zinc. Except in the cases of nickel and copper, the new masses agree reasonably well with the results of previous investigations.

The isotopic assignment of neutron capture $\gamma$ rays in the above elements has been examined using the new data and several new ($n, \gamma$) reaction $Q$ values result. Comparison between measured stable isotope mass differences and the mass differences calculated from nuclear disintegration energies shows no outstanding discrepancy in this region, assuming the new ($n, \gamma$) assignments to be correct.

From nuclear energy data a complete mass table has been calculated for these five elements and the resulting masses used to investigate nucleon binding energies. The binding energy of the last proton or last neutron in the nucleus shows a reasonably consistent variation with mass. Pairing energies for the last neutron and last proton pairs have also been calculated wherever sufficient mass data exist. Only partial correlation seems possible between pairing energy and the angular momentum of the level occupied by the pair.

• Received 5 July 1956

DOI:https://doi.org/10.1103/PhysRev.104.461