Paths to Superheavy Nuclei

TL;DR

This work synthesizes the FRIB-TA topical program 'The path to Superheavy Isotopes' (June 2024), outlining the problem of predicting and guiding the synthesis of superheavy nuclei (SHN) and identifying the necessary theoretical developments to complement experimental efforts. It emphasizes a traditional three-phase production picture—$\sigma_{ER}=\sum_l \sigma_{cap}(l,E)\,P_{CN}(l,E,E_x)\,W_{surv}(l,E_x)$—and surveys a suite of modeling frameworks (TDHF, stochastic dynamics, Fusion-by-Diffusion, DNS, CC methods, coherence dynamics, and hybrid models) while underscoring the need for robust uncertainty quantification. The report highlights critical theory needs across capture, CN formation, and evaporation, including improved fission-barrier and level-density inputs, along with a detailed program for multinucleon transfer and UQ pipelines to constrain predictions. It also discusses experimental strategies (e.g., at LBNL) to benchmark theory, explores alternative production avenues (MNT, doorway states, r-process-like channels, astrophysical sites), and argues for a strengthened international SHN theory community to enable reliable predictions and guide discovery potential.

Abstract

This document summarizes the discussions and outcomes of the Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program "The path to Superheavy Isotopes" held in June 2024 at FRIB. Its content is non-exhaustive, reflecting topics chosen and discussed by the participants. The program aimed to assess the current status of theory in superheavy nuclei (SHN) research and identify necessary theoretical developments to guide experimental programs and determine fruitful production mechanisms. This report details the intersection of SHN research with other fields, provides an overview of production mechanisms and theoretical models, discusses future needs in theory and experiment, explores other potential avenues for SHN synthesis, and highlights the importance of building a strong theory community in this area.

Figures (6)

• Figure 1: Coexisting configurations associated with different density distributions predicted by nuclear DFT for the hypothetical superheavy nucleus $^{780}254_{526}$. Three topologies are considered: normal nuclear densities similar to those found in stable nuclei, bubble nuclei distinguished by a substantial dip at the center, and band configurations forming a thin band of nuclear matter wound into a torus. The contour plots of the total densities are given in the boxes. (From Ref. Nazarewicz2002).
• Figure 2: An attempt to place the superheavy elements into the Periodic Table according to Dirac-Fock and configuration-interaction calculations Savelyev2023. The unambiguous placement of elements $Z=121$, 122, 123, 124, and 168, the double placement of $Z=145$, and doubly occupied and vacant entries in the $8^{\text{th}}$ period highlight the breakdown of Periodic Table periodicity for superheavy elements. (From Ref. Smits2023).
• Figure 3: Cartoon illustrating the traditional three-phase model of superheavy nucleus formation: capture, compound nucleus formation, and evaporation.
• Figure 4: Typical timescales of heavy-ion collision stages at energies near the Coulomb barrier.
• Figure 5: Visual overview of theoretical methods used in describing fusion dynamics towards superheavy nuclei.