Superheavy Nuclei

Abstract

The semiempirical mass formula and other data previously extrapolated by one of us indicated possible existence of nuclei with mass values up to twice the largest now known. Here this mass region is further explored. Extrapolations are revised and the properties of such superheavy nuclei are estimated in more detail. Despite $Z$ values substantially higher than 137, the $K$ electrons behave perfectly normally because of the finite extension of the nucleus. Vacuum polarization and vacuum fluctuations are roughly estimated to make relatively minor alterations in the $K$ electron binding—which exceeds $m{c}^2$. The effect of nuclear attraction in speeding up beta decay is calculated approximately. Calculated beta lives are never much less than ${10}^{-4\mathrm{}}$ sec. Beta decay energies and neutron binding energies are calculated from the semiempirical mass formula. Fission barriers and cross sections for the ($n, \gamma$) process are estimated. Branching ratios in beta decay are calculated for the processes of simple beta decay and for "delayed" neutron emission and "delayed" fission. The latter quantity sets an irreducible minimum to the losses that occur in the process of buildup under even the heaviest neutron flux. The calculated fractional yield of nuclei which reach $Z=147\mathrm{}$, $A=500\mathrm{}$ is >0.05. Under a lower flux the losses are greater. All stability calculations in this paper depend upon substantial extrapolations, with complete disregard of shell effects and other particularities that may be important, and therefore can be completely in error. Conversely, observation of existence or absence of superheavy nuclei with lives less than a second should test stringently the semiempirical mass formula and the semiempirical estimates of spontaneous fission barriers.