The 16-in. double-focusing mass spectrometer at the University of Minnesota has been employed to measure the atomic mass of 42 stable isotopes in the region $A=69\mathrm{} \mathrm{to} 100$. The standard error associated with these results is approximately 5 parts in ${10}^8$. Improvements in the instrument are described that result in an increase of useful resolution of a factor of 2 to 3. A set of 64 radioactive masses is calculated from the stable mass data together with $\beta$-decay energies and nuclear reaction $Q$ values. The resultant table of masses is used to calculate total nuclear binding energies, separation energies and pairing energies for a number of nuclei in the region near $N=50\mathrm{}$. The systematics of the separation energies display very smooth characteristics except at the shell closure. Neutron pairing energies show a marked decrease in value following the shell closure.

• Received 14 June 1963

DOI:https://doi.org/10.1103/PhysRev.132.1662