The 16-in. double-focusing mass spectrometer at the University of Minnesota has been employed to measure the atomic mass of ${\mathrm{H}}^1$ and the atomic masses and isotopic mass differences of chlorine, barium, cerium, and neodymium. Recent improvements in instrumentation have increased the precision of both narrow and wide doublet measurements. The doublet ${\mathrm{C}}_{11}$${\mathrm{H}}_{22}$-${\mathrm{C}}_{12}$${\mathrm{H}}_{10}$ was used to relate the ${\mathrm{H}}^1$ mass directly to the ${\mathrm{C}}^{12}$ mass standard with a precision of ±30 eV. The chlorine masses obtained in this investigation have a precision greater than previous measurements and provide further information about disagreements which were present in previous work. Additional atomic masses are calculated from the stable-mass data of barium, cerium, and neodymium, together with alpha-decay, beta-decay, and nuclear-reaction energies. The resultant table of masses is used to calculate nuclear systematic energies in the region near $N=82\mathrm{}$. The systematics of the separation energies display very smooth characteristics except at the shell closure of $N=82\mathrm{}$ and are so regular as to be a powerful aid in the evaluation of some possible errors in reaction and decay data used in the calculation of these nuclear systematics.

• Received 30 August 1965

DOI:https://doi.org/10.1103/PhysRev.141.1112