Examining the stability of thermally fissile Th and U isotopes

The properties of recently predicted thermally fissile Th and U isotopes are studied within the framework of the relativistic mean-field approach using the axially deformed basis. We calculate the ground, first intrinsic excited state for highly neutron-rich thorium and uranium isotopes. The possible modes of decay such as $\alpha$ decay and $\beta$ decay are analyzed. We found that neutron-rich isotopes are stable against $\alpha$ decay, however, they are very unstable against $\beta$ decay. The lifetime of these nuclei is predicted to be tens of seconds against $\beta$ decay. If these nuclei are utilized before their decay time, a lot of energy can be produced with the help of multifragmentation fission. Also, these nuclei have great implications from the astrophysical point of view. In some cases, we found that the isomeric states with energy range from 2 to 3 MeV and three maxima in the potential energy surface of ${}^{228-230}\mathrm{Th}$ and ${}^{228-234}\mathrm{U}$ isotopes.

Figure 1

Variations of the (a) calculated binding energy (BE), (b) charge radius ($r_c$), and (c) quadrupole deformation parameter (${\beta }_2$) are given with the bosonic and fermionic basis.

Figure 2

The potential energy surface is a function of the quadrupole deformation parameter (${\beta }_2$) for Th isotopes. The difference between the leftmost (blue) and the middle (green) circles represents the first fission barrier height $B_f$ (in MeV). See text for details.

Figure 3

Same as Fig. 2, but for U isotopes.

Figure 4

Single-particle energy levels for ${}^{232}\mathrm{Th}$ as a function of the quadrupole deformation parameter ${\beta }_2$. Fermi levels are denoted by the dotted (red) curve.

Figure 5

Same as Fig. 4, but for the ${}^{236}\mathrm{U}$ nucleus.

Figure 6

The $Q_{\alpha }$ and half-life time $T_{1/2}^{\alpha }$ of the $\alpha$-decay chain for Th isotopes are calculated using the RMF, FRMD [28, 29], and ELDM [52] and compared with the experiment (EXP.) [30].

Figure 7

Same as Fig. 6, but for U.

Figure 8

The $\beta$-decay half-lives for Th and U isotopes are calculated using the formula of Fiset and Nix [55] [Eq. (24)]. Ground-state binding energies are taken from the FRDM [29], INM [56], and RMF models.