Examining the enhancement of sub-barrier fusion cross sections by neutron transfer with positiveQ values

Abstract

Background: Significant enhancement of sub-barrier fusion cross sections owing to neutron rearrangement with positive Q values were found for many combinations of colliding nuclei. However, several experimental results on fusion reactions were reported recently in which such enhancement has not been observed in spite of a possibility for neutron rearrangement with positive Q values. Purpose: We aim to clarify much better the mechanism of neutron rearrangement in sub-barrier fusion reactions to find the other requirements (beside positive Q values) which favor (or prevent) sub-barrier fusion enhancement. Methods: A channel coupling approach along with the semiclassical model for neutron transfer has been used for analysis of available experimental data on sub-barrier fusion of heavy ions. Results: The role and interplay of different factors determining the enhancement of sub-barrier fusion (such as Q values for neutron rearrangement, properties of collective excitations, and neutron binding energies) have been studied and clarified. Conclusions: (1) Only 1n and 2n transfers with positive Q values have a noticeable impact on sub-barrier fusion. A positive Q value for neutron rearrangement is a necessary but not sufficient requirement for additional sub-barrier fusion enhancement to take place. (2) The "rigidity" of colliding nuclei with respect to collective excitations is important for sub-barrier fusion enhancement due to neutron rearrangement with positive Q values to be clearly visible. (3) The neutron binding energy of the "donor" nucleus has a strong impact only in the case of fusion of light weakly bound nuclei.

Breakup and n -transfer effects on the fusion reactions Li6,7+Sn120,Fisichella1, Shotter2, Фігуера3 et al. 2017Phys. Rev. C19030View full textAdd to dashboardCite

“…11) are very close in spite of the different n-transfer Q values. This behavior seems to be consistent with the one observed in fusion reactions of heavier systems [17][18][19] and appears to confirm the idea, proposed in [21][22][23], that it is not just the difference in the n-transfer Q value itself which generates a modification of the behavior of the fusion cross section.…”

“…Therefore, within this approach, in systems where transfer does not modify significantly the deformation of the colliding nuclei there is little effect on the fusion cross section. Similar conclusions were reached in [23].…”

Cross sections for the production of superheavy nuclei

“…Recent systematic study of the problem [18] shows that all available experimental data on near barrier fusion reactions are described quite properly within this model. An example of such agreement is shown in Fig.…”

“…Note, that for the practical applications (calculation of the cross sections) we use the empirical channel coupling model. At the same time, the existing approximations to the CC approach with [18] and without [20] accounting for neutron rearrangement could be also useful for data analysis and/or better qualitative understanding of the underling physics.…”

Influence of neutron transfer channels on fusion enhancement in sub-barrier region

“…However, in few recent work, in spite of positive Q-values, no effect of the transfer channel on fusion enhancement was observed [10][11][12]. Apart from this, it was demonstrated in a literature that only outermost neutrons (up to two neutrons) of nuclei give a significant contribution to the fusion enhancement [13]. The importance of two neutrons pick-up channel was also highlighted for system 40 Ca + 64 Ni whose experimental data was well reproduced by coupling with two neutron transfer.…”