Atomic Masses in the Region Xenon to Europium

Abstract

A six-inch double-focusing mass spectrometer employing the peak matching method of measurement has been used to measure 36 atomic masses in the region $130\leqq A\leqq 154$ and $54\leqq Z\leqq 63$. Atomic masses of 41 radioactive nuclei have then 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 $N=82\mathrm{}$ on the systematics of nuclear binding and pairing energies has been investigated in greater detail than has previously been possible. The discontinuity in neutron binding energy, observed in reaction measurements and $\beta$-decay systematics, is shown to be caused by a decrease in binding energy of neutrons beyond $N=82\mathrm{}$ rather than a particular large binding energy at $N=82\mathrm{}$. The systematic behavior of proton binding and pairing energies is also studied. The nucleon binding and pairing energy results show departures from uniformity in the region near $N=90\mathrm{}$. Electric quadrupole systematics have also indicated a change in nuclear structure in this region. The present atomic masses are also employed in the isotopic identification of several reactions, in the study of several natural alpha decays, and in the interpretation of several $\beta$-decay disintegration schemes.