The Missing Heavy Nuclei

Considerations of the regularities in the distribution of isotopes lead to the following conclusions. (1) Rn, AcA, ThA, and RaA should all be somewhat beta-active but the branching ratios would be too small for detection of the activity except for Rn and RaA. (2) ${}_{93}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Re}}^{239}$ should be beta-active with a roughly estimated half-life of about 1 month, ${}_{93}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Re}}^{237}$ should be an alpha-emitting nucleus, and ${}_{92}{}^{}{}_{}{}^{}\mathrm{U}_{}^{237}{}_{}{}^{}$ should be beta-active. (3) The heaviest beta-stable isotopes of transuranic elements should be as follows: ${}_{93}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Re}}^{237}$, ${}_{94}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Os}}^{244}$, ${}_{95}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Ir}}^{243}$, ${}_{96}{}^{}{}_{}{}^{}\mathrm{Eka}$ ${\mathrm{Pt}}^{250}$. It is shown that isotopes of transuranic elements should undergo fission upon exposure to slow neutrons, which may account for their absence in nature. Their presumable greater probability for spontaneous fission might also account for their absence. The relative abundance of ${\mathrm{U}}^{235}$ and ${\mathrm{U}}^{238}$ is in fair agreement with the hypothesis that the amount of ${\mathrm{U}}^{235}$ was determined by a balance between production from ${\mathrm{U}}^{239}$ and loss by fission. The probable chain of disintegrations of $4n+1$ nuclei is discussed. The estimated half-lives of all are too short for them to have survived. Their absence is to be attributed to the absence of a possible long-lived transuranic ancestor. Either the hypothetical irradiation by neutrons or spontaneous fission of a transuranic ancestor will account for the low abundance of ${\mathrm{Bi}}^{209}$.