Exploring quasifission dynamics in reactions leading to the formation of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Pa</mml:mi><mml:mprescripts/><mml:none/><mml:mn>225</mml:mn></mml:mmultiscripts></mml:math>
Аннотация
Background: Understanding the dynamics of quasifission reactions for the pre-actinides and actinides is particularly important for choosing suitable target projectile combinations to synthesize of superheavy elements. Measurements of fission-fragment mass distributions by us in reactions populating the pre-actinides nuclei $^{200}\mathrm{Pb}$ showed no indication of the presence of quasifission, contrary to two recent claims from the state-of-the-art theoretical calculations that predicted noncompound nuclear reaction in these reactions.Purpose: The purpose was to investigate the signature of noncompound nuclear fission, if any, in the fission of $^{225}\mathrm{Pa}$ populated via two different entrance channels $^{20}\mathrm{Ne}+^{205}\mathrm{Tl}$ and $^{16}\mathrm{O}+^{209}\mathrm{Bi}$.Methods: Two position-sensitive multiwire proportional counters were placed at the folding angle to detect the fission fragments. Mass distributions were extracted from the measured time-of-flight differences and position information ($\ensuremath{\theta},\ensuremath{\phi}$) of the fission fragments.Results: The mass distributions for both reactions are found to be symmetric at all the measured energies up to the excitation energy of 110 MeV. The variation of the standard deviations of mass distributions increases smoothly with excitation energy. The theoretical calculation indicates a significant amount of quasifission in the mass asymmetric region in both reactions.Conclusion: The measured fission-fragment mass distributions for the two reactions that populated the same compound nucleus, do not provide evidence of quasifission in the mass symmetric region.