JINR model describes alpha decay, cluster radioactivity and fission of heavy nuclei in one framework
A theoretical model from JINR with two collective parameters reproduced measured half-lives of isotopes from uranium to hassium, which differ by tens of orders of magnitude.
Scientists at the Joint Institute for Nuclear Research (JINR) have proposed a single theoretical model that describes three decay modes of heavy and superheavy nuclei: alpha decay, cluster radioactivity and spontaneous fission, according to Poisk. These processes were usually treated separately, although in each case the parent nucleus splits into two parts poisknews.ru
Поискpoisknews.ruOpen source ↗. The model uses two collective parameters: charge asymmetry and the distance between the centers of the future fragments.
How the model works
The ground state of a heavy nucleus is treated as a sum of a "mono-configuration" and small contributions from dinuclear systems, that is, pairs of clusters. Decay is split into two stages: a suitable pair of fragments must first form, and then it must separate by overcoming a potential barrier. For alpha decay, barrier penetrability plays the key role; for cluster radioactivity both stages matter. In spontaneous fission the barrier along the distance between fragments is often already absent, so the lifetime is determined mainly by the probability of forming the fissioning configuration.
The model was tested on isotopes of uranium, plutonium, curium, californium, fermium, nobelium, rutherfordium, seaborgium and hassium. The calculations reproduced experimental half-lives, which can differ by tens of orders of magnitude.
Isotopic trends and K isomers
The model explains the known enhanced stability of fermium and nobelium isotopes with neutron number N = 152 and the weaker manifestation of this effect in rutherfordium and seaborgium. The calculations also predict stability features near N = 162 for alpha decay and N = 164 for spontaneous fission poisknews.ru
Поискpoisknews.ruOpen source ↗.
Half-lives for spontaneous fission from K-isomeric states of actinides and superheavy nuclei were calculated for the first time. The decay of such states depends on a competition of two factors: increasing spin usually hinders fission, while the isomer energy can facilitate it. For even-odd nuclei, the authors linked the spontaneous-fission hindrance factor to the nuclear spin, which changes the barrier height through the rotational potential; the largest contribution comes from the configuration containing an alpha particle.
Another result is a method for estimating nuclear spin from the delay of spontaneous fission in experimental alpha-decay chains. The authors applied it to the chains of darmstadtium isotopes 273Ds and 275Ds. The study was published in the journal Physics of Particles and Nuclei.
