Eur. Phys. J. A (2026) 62: 92
https://doi.org/10.1140/epja/s10050-026-01859-8

Code Paper

QMFTMD a code for fission mass distribution within quantum mechanical fragmentation theory-application to Hg isotopes

Department of Physics, Bharathiar University, 641046, Coimbatore, Tamil Nadu, India

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Received: 10 January 2026
Accepted: 9 April 2026
Published online: 12 May 2026

Abstract

Experimental investigations using (p,f) and ($\alpha$,f) reactions on nuclei near the $\beta$-stability line in the mass range A = 190–200 have revealed symmetric fission fragment distributions. However, the experimental observation of an asymmetric mass distribution in the $\beta$-delayed fission of excited $_{}^{180}$Tl has triggered renewed theoretical and experimental interest in understanding the fission dynamics within the pre-actinide region. We investigate the mass distribution of neutron-deficient to neutron-rich even-mass Hg isotopes in the mass range from 178 to 200 within the framework of the quantum mechanical fragmentation theory (QMFT) based on the two-centre shell model. A dedicated Python code QMFTMD has been developed to numerically evaluate fission fragment mass yield distributions. Without temperature and deformation effect, $_{}^{178}$Hg–$_{}^{186}$Hg show symmetric mass distributions, which become asymmetric from $_{}^{188}$Hg to $_{}^{200}$Hg. Introducing deformation (at $T=0$ MeV) yields asymmetric distributions from $_{}^{178}$Hg–$_{}^{190}$Hg and symmetric ones from $_{}^{192}$Hg onward. With both deformation and temperature ($T=1.5$ MeV), a similar trend persists with magnitude changes. The inclusion of nuclear deformation alone is sufficient to drive the transition from asymmetric to symmetric fission fragment mass distributions across the even-mass Hg isotopes. The results are compared with experimental data and GEF calculations for $_{}^{180}$Hg and $_{}^{198}$Hg. Overall, the obtained results successfully capture the qualitative features of the experimental trends in the pre-actinide region, providing an understanding of the mechanisms governing fission in neutron-deficient and neutron-rich mercury isotopes.