Search for long lived heaviest nuclei beyond the valley of stability

Abstract

The existence of long lived superheavy nuclei (SHN) is controlled mainly by spontaneous fission and \ensuremath{\alpha}-decay processes. According to microscopic nuclear theory, spherical shell effects at $Z=114$, 120, 126 and $N=184$ provide the extra stability to such SHN to have long enough lifetime to be observed. To investigate whether the so-called ``stability island'' could really exist around the above $Z$, $N$ values, the \ensuremath{\alpha}-decay half-lives along with the spontaneous fission and \ensuremath{\beta}-decay half-lives of such nuclei are studied. The \ensuremath{\alpha}-decay half-lives of SHN with $Z=102$--120 are calculated in a quantum tunneling model with DDM3Y effective nuclear interaction using ${Q}_{\ensuremath{\alpha}}$ values from three different mass formulas prescribed by Koura-Uno-Tachibana-Yamada (KUTY), Myers-Swiatecki (MS), and Muntian-Hofmann-Patyk-Sobiczewski (MMM). Calculation of spontaneous fission (SF) half-lives for the same SHN are carried out using a phenomenological formula and compared with SF half-lives predicted by Smolanczuk et al. A possible source of discrepancy between the calculated \ensuremath{\alpha}-decay half-lives of some nuclei and the experimental data of GSI, JINR-FLNR, RIKEN, is discussed. In the region of $Z=106$--108 with $N~$ 160--164, the \ensuremath{\beta}-stable SHN ${}_{106}^{268}{\text{Sg}}_{162}$ is predicted to have highest \ensuremath{\alpha}-decay half-life (${T}_{\ensuremath{\alpha}}~3.2$ h) using ${Q}_{\ensuremath{\alpha}}$ value from MMM. Interestingly, it is much greater than the recently measured ${T}_{\ensuremath{\alpha}}$ ($~22$ s) of deformed doubly magic ${}_{108}^{270}{\text{Hs}}_{162}$ nucleus. A few fission-survived long-lived SHN which are either \ensuremath{\beta}-stable or having large \ensuremath{\beta}-decay half-lives are predicted to exist near ${}^{294}{110}_{184}$, ${}^{293}{110}_{183}$, ${}^{296}{112}_{184}$, and ${}^{298}{114}_{184}$. These nuclei might decay predominantly through \ensuremath{\alpha}-particle emission.