Hyperheavy nuclei: existence and stability

TL;DR

This study uses covariant density functional theory to identify stable regions of hyperheavy nuclei with proton numbers above 126, revealing three spherical regions and emphasizing the importance of triaxiality in nuclear stability.

Contribution

First demonstration of stable hyperheavy nuclei regions around Z~138, 156, 174 using covariant density functional theory, highlighting the role of triaxiality in stability boundaries.

Findings

Identified three spherical hyperheavy nuclei regions with potential stability.

Stability boundaries are primarily determined by spontaneous fission, not particle emission.

Triaxiality significantly reduces the stability of hyperheavy nuclei.

Abstract

What are the limits of the existence of nuclei? What are the highest proton numbers $Z$ at which the nuclear landscape and periodic table of chemical elements cease to exist? These deceivably simple questions are difficult to answer especially in the region of hyperheavy ($Z\geq 126$) nuclei. We present the covariant density functional study of different aspects of the existence and stability of hyperheavy nuclei. For the first time, we demonstrate the existence of three regions of spherical hyperheavy nuclei centered around ($Z\sim 138, N\sim 230$), ($Z\sim 156, N\sim 310$) and ($Z\sim 174, N\sim 410$) which are expected to be reasonably stable against spontaneous fission. The triaxiality of the nuclei plays an extremely important role in the reduction of the stability of hyperheavy nuclei against fission. As a result, the boundaries of nuclear landscape in hyperheavy nuclei are defined by spontaneous fission and not by the particle emission as in lower $Z$ nuclei. Moreover, the current study suggests that only localized islands of stability can exist in hyperheavy nuclei.