A sixteen-inch double-focusing mass spectrometer employing the peak matching method of measurement has been used to measure the atomic masses of all stable isotopes in the region ruthenium to xenon. Atomic masses of 53 radioactive nuclei have been calculated from mass differences derived from nuclear reaction and $\beta$-decay energies. Nucleon binding and pairing energies have been calculated from the resulting mass table. The effect of the shell closure at $Z=50\mathrm{}$ on the systematics of nucleon binding and pairing energies has been investigated in greater detail than has previously been possible. The discontinuity in proton binding energy is shown to be caused by a decrease in binding energy of protons beyond $Z=50\mathrm{}$. The main result of the study of nuclear systematics in this region seems to be that the binding energies of both neutrons and protons exhibit smooth behavior except for discontinuities at a shell closure. The presence of doubly charged, diatomic tellurium satellites which interfere with the singly charged ion peaks is also noted.

• Received 14 June 1963

DOI:https://doi.org/10.1103/PhysRev.132.1673