Exploring quasifission characteristics for ³⁴S+²³²Th forming ²⁶⁶Sg

Abstract

Background: Fission fragments from heavy ion collisions with actinide nuclei show mass-asymmetric and mass-symmetric components. The relative probabilities of these two components vary rapidly with beam energy with respect to the capture barrier, indicating a strong dependence on the alignment of the deformed nucleus with the partner in the collisions. Purpose: To study the characteristics of the mass-asymmetric quasifission component by reproducing the experimental mass-angle distributions to investigate mass evolution and sticking times. Methods: Fission fragment mass-angle distributions were measured for the 34S + 232Th reaction. Simulations to match the measurements were made by using a classical phenomenological approach. Mass ratio distributions and angular distributions of the mass-asymmetric quasifission component were simultaneously fit to constrain the free parameters used in the simulation. Results: The mass-asymmetric quasifission component—predominantly originating from tip (axial) collisions with the prolate deformed 232Th—is found to be peaked near A = 200 at all energies and center-of-mass angles. A Monte Carlo model using the standard mass equilibration time constant of 5.2 × 10−21 s predicts more symmetric mass splits. Three different hypotheses assuming (i) a mass halt at A = 200, (ii) a slower mass equilibration time, or (iii) a Fermi-type mass drift function reproduced the main experimental features. Conclusions:In tip collisions for the 34S + 232Th reaction, mass-asymmetric fission with A ∼ 200 is the dominant outcome. The average sticking time is found to be ∼7 × 10−21 s, independent of the scenario used for mass evolution.