Competing asymmetric fusion-fission and quasifission in neutron-deficient sub-lead nuclei

Hg178 and asymmetric fission of neutron-deficient pre-actinides

“…the pre-neutron A pre and TKE distributions. These correspond to the bulk of information collected so far in the region for low-energy fission [9,20,28,29,33,[49][50][51][52][53][54][55][56][57][58][59][60]. The present work supplements the existing set of systems with 178 Hg, and discusses its features in the context of the asymmetric-fission island southwest of 208 Pb.…”

Evidence for the general dominance of proton shells in low-energy fission

“…Clear evidence of asymmetric fission in pre-actinides near β stability, namely in 201 Tl, was established in light-ion induced fission by Itkis et al [7]. The recent observation of almost exclusively asymmetric fission in the neutron-deficient 180 Hg, for which two doubly-magic 90 Zr fragments were expected [21] has led to a resurgence of interest in fissioning pre-actinides, and measurements of additional systems [22][23][24][25][26][27][28] ascertained the occurence of asymmetric fission over an enlarged domain around lead. Finally, a consistent understanding of the fragment properties running from the "old" (actinide) to the "new" (pre-actinide) region of asymmetric fission is still missing [3,29].…”

“…The asymmetric components, clearly visible in the β-delayed [21,22] and electromagnetic-induced [23] fission experiments, in terms of the mean position of the light and heavy partners, in either mass A L,H or charge Z L,H depending on availability, are deduced from the measured fragment A (or Z) distributions. As for the fusion-induced fission approach, the location of the asymmetric peaks was determined in the corresponding references [24][25][26][27][28] based on the adjustment of the mass distribution by a superposition of Gaussian functions. The mean neutron and/or proton numbers of the fission partners are then derived in this work under the Unchanged-Charge-Density (UCD) assumption [32].…”

“…FIG.1: Mean (a) proton Z L(H) and (b) neutron N L(H ) numbers of the light (heavy) fragment as a function of fissioning system ZCN and NCN , respectively, from fusion-(red), β-delayed-(blue) and electromagnetic-induced (green) fission[7,[21][22][23][24][25][26][27][28]. The best fits and ZL= 36 are shown as continuous and dashed lines, respectively.…”

“…For clarity, isotopes of a same element are shifted according to mass. The points are from Refs [7,15,18,19,[21][22][23][24][25][26][27][28]. and therein.…”