Atomic Masses in the Heavy Mass Region

A six-inch double-focusing mass spectrometer has been employed to determine 61 mass doublets in the region of gadolinium to gold. The present results and other Minnesota mass data have been combined with nuclear reaction, β-decay, and α-decay energies in order to construct a mass table for more than 200 stable and radioactive isotopes in the region from samarium to radon. Total atomic binding energies as well as nucleon separation and pairing energies have been computed, wherever possible.The present data confirm with greater detail the previously reported anomalies in the nucleon separation and pairing energies in the regions around 90 neutrons and 116 neutrons. The proton pairing energies are found to show rather pronounced "maxima" around $N=88$ and $N=116$, a behavior similar to the previously reported behavior of neutron pairing energies. The nature of the discontinuities in these two regions does not appear to follow the patterns found at major shell closures but seems to be caused by a change in the nuclear structure in these regions. It is known that such a change is indicated also by other nuclear properties.Major discontinuities connected with the shell closures at $Z=82$ and $N=126$ are brought out in greater detail than has previously been possible.The mass data have also been employed for the study of isotopic assignments for several nuclear reactions in this region.