Influence of entrance-channel magicity and isospin on quasi-fission

Systematic study of quasifission characteristics and timescales in heavy element formation reactions

“…Quasifission mass-angle distributions (MAD) first measured at GSI in the 1980s [2,5] showed that quasifission timescales could often be shorter than the rotation time of ∼10 −20 s. However, subsequently only a few measurements [6,7] were made until recent years, when an extensive series of experiments (using the Australian National University Heavy Ion Accelerator Facility and CUBE spectrometer) were carried out [3,[8][9][10][11][12][13][14][15][16]. The kinematic coincidence technique used in the measurements [2,3,17] provides direct information on the mass-ratio of the fragments at scission; thus, the data are represented in terms of mass ratio M R , rather than pre-or According to the characteristics of the MAD (minimum mass yield at symmetry, mass-angle correlation with peak yield at symmetry, and no significant mass-angle correlation), they are assigned as type MAD1, MAD2 and MAD3 respectively [3].…”

“…There is a clear correlation between the MAD class and the entrance channel charge product. Other entrance channel characteristics are important in determining the sticking times and MAD characteristics, including neutron richness [14,18], and shell structure including static deformation [11] and magic numbers [14].To improve our quantitative understanding of the role of shell structure in the dynamics of quasifission, we make an analogy with the liquid drop model approach to nuclear masses, in which localized shell effects can be quantified when the underlying smooth (liquid drop) trends are well defined. To define the smooth trends in quasifission, a large number of MAD measurements have been selected, for beam energies somewhat above the capture barrier (typically by ∼ 6%).…”

“…There is a clear correlation between the MAD class and the entrance channel charge product. Other entrance channel characteristics are important in determining the sticking times and MAD characteristics, including neutron richness [14,18], and shell structure including static deformation [11] and magic numbers [14].…”

Microscopic study ofCa40+Ni58,64fusion reactions

“…Similar times were obtained for near barrier collisions in lighter [38,71] and similar [14,28] mass regions. These times are relatively short in comparison with heavier systems computed with TDHF where typical contact times of few zeptoseconds [72] or more in case of quasi-fission reactions [43,53,[73][74][75] are often obtained, leading to possible large mass transfer [76,77]. Nevertheless, contact times of ∼ 1 zs are long enough to allow transfer of one or more nucleons [23,30,31,78], in particular in the case of positive Q value reactions as will be seen in section III C. The resulting fusion thresholds are listed in Table I.…”

Fusion – fission dynamics: fragment mass distribution studies

“…Two kinds of shell-effects on the di-nuclear system have been observed. The first one is due to shell closures in the entrance channel [28], the second one, as studied here in the case of fusion fission, is due to shell-effects in final fragments [29][30][31]. It is known that with the increase in excitation energy, nuclear shell effect decreases.…”