Competing decay modes and stability analysis of superheavy nuclei with Z = 120 using relativistic mean-field approach

TL;DR

We address the stability of $Z=120$ superheavy nuclei with $256 le A le 304$, focusing on the competition between α-decay and spontaneous fission. Predictions are obtained with a fully microscopic RMF NL3 input in the Preformed Cluster Decay Model (PCM), using double-folding NN potentials with both M3Y and R3Y, and results are benchmarked against the Universal Decay Law (UDL), Horoi-type formulas, and the Xu et al. SF prescription. The analysis finds extended α-decay chains toward fermium for $296 le A le 304$, with maxima in $\\log_{10} T_{1/2}$ near neutron numbers $N ≈ 166$–$182$, and identifies $^{296}$120, $^{298}$120, $^{300}$120, $^{302}$120, and $^{304}$120 as particularly favorable against SF. The study highlights the crucial roles of shell effects, deformation, and pairing in shaping $Q_α$, the preformation factor $P_0$, and the barrier properties, offering a self-consistent microscopic framework to guide future experimental searches for $Z=120$.

Abstract

We systematically study the competition between α-decay and spontaneous fission in even-even superheavy nuclei with (Z=120) and 256 \leq A \leq 304 within the preformed cluster-decay model using microscopic inputs from relativistic mean-field calculations with the NL3 parameter set. The α-decay half-lives are obtained from WKB barrier penetration with empirically determined preformation factors, self-consistent Q_α values from RMF, and nuclear interaction potentials constructed using both M3Y and relativistic R3Y nucleon-nucleon forces, and are benchmarked against standard semi-empirical formulas. Our results predict reduced spontaneous fission probabilities and extended α-decay chains toward the fermium region for isotopes with 296 \leq A \leq 304, with enhanced stability reflected in maxima of log_{10} T_{1/2} around neutron numbers N \approx 166-182. In particular, the nuclei 296,298,300,302,304_{120} are identified as the most favorable candidates for survival against fission, demonstrating the crucial role of shell effects, deformation, and pairing correlations and providing quantitative guidance for future experimental searches of Z=120 nuclei.

Figures (5)

• Figure 1: (Color online) The total ($V_{T}$) nucleus-nucleus interaction potential (in MeV) and its components - nuclear and Coulomb potentials - are presented as a function of the radial separation $R$ (in fm) for the M3Y (NL3) and R3Y NN potentials, using the alpha decay $^{304}$120 $\rightarrow$$^{300}$Og + $\alpha$ as a representative case. The inset provides a magnified view of the barrier height and its position corresponding to the total interaction potentials.
• Figure 2: (Color online) The $\alpha$-decay (Q$_{\alpha}$) energies for five different Z = 120 chains, namely, $^{296}120$$\rightarrow$$^{256}$Fm, $^{298}120$$\rightarrow$$^{258}$Fm, $^{300}120$$\rightarrow$$^{260}$Fm, $^{302}120$$\rightarrow$$^{262}$Fm, and $^{304}120$$\rightarrow$$^{264}$Fm, calculated using RMF (NL3), are given along with the available experimental data wang12. See text for details.
• Figure 3: (Color online) The variation of preformation probability w.r.t. the neutron number for five isotopes of Z = 120 chains, namely, $^{296}120$$\rightarrow$$^{256}$Fm, $^{298}120$$\rightarrow$$^{258}$Fm, $^{300}120$$\rightarrow$$^{260}$Fm, $^{302}120$$\rightarrow$$^{262}$Fm, and $^{304}120$$\rightarrow$$^{264}$Fm.
• Figure 4: (Color online) The $\alpha$-decay half-life ($T_{1/2}^{\alpha}$) for five different Z = 120, namely, $^{296}120$$\rightarrow$$^{256}$Fm, $^{298}120$$\rightarrow$$^{258}$Fm, $^{300}120$$\rightarrow$$^{260}$Fm, $^{302}120$$\rightarrow$$^{262}$Fm, and $^{304}120$$\rightarrow$$^{264}$Fm, calculated using R3Y and M3Y potential are given along with the UDL isma24, HOROI isma24 formulae, and available experimental data Audi17audi21. SF denotes spontaneous fission. The decay modes and their intensities in percentages are also given along with the experimental data. A question mark (?) alone indicates a decay mode which is energetically allowed but has not yet been observed experimentally. See text for details.
• Figure 5: (Color online) The estimated $\log_{10}b$ for five different Z = 120 chains, namely, $^{296}120$$\rightarrow$$^{256}$Fm, $^{298}120$$\rightarrow$$^{258}$Fm, $^{300}120$$\rightarrow$$^{260}$Fm, $^{302}120$$\rightarrow$$^{262}$Fm, and $^{304}120$$\rightarrow$$^{264}$Fm, calculated using R3Y and M3Y potential within the PCM framework are given along with the UDL isma24, and HOROI isma24 formulae. See text for details.