Exploring quasifission characteristics for +232Th34S 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 +232Th34S 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 +232Th34S 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.- Publication:
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Physical Review C
- Pub Date:
- February 2016
- DOI:
- 10.1103/PhysRevC.93.024607
- Bibcode:
- 2016PhRvC..93b4607P