Channel coupling effects on the fusion excitation functions forSi28+Zr90,94

Abstract

Fusion excitation functions and angular distributions of evaporation residues (ERs) have been measured for 28 Si + 90,94 Zr systems around the Coulomb barrier using the recoil mass spectrometer, Heavy Ion Reaction Analyzer (HIRA). For both systems, the experimental fusion cross sections are strongly enhanced compared to the predictions of the one-dimensional barrier penetration model (1-d BPM) below the barrier. Coupled channels formalism has been employed to theoretically explain the observed sub-barrier fusion cross section enhancement. The enhancement could be explained by considering the coupling of the low-lying inelastic states of the projectile and target in the 28 Si + 90 Zr system. In the sub-barrier region, the measured fusion cross sections for 28 Si + 94 Zr turned out to be about an order of magnitude higher than the ones for the 28 Si + 90 Zr system, which could not be explained by coupling to inelastic states alone. This observation indicates the importance of multinucleon transfer reaction channels with positive Q values in the sub-barrier fusion cross section enhancement, because 90,94 Zr are believed to have similar collective strengths. This implies that no strong isotopic dependence of fusion cross sections is expected as far as the couplings to collective inelastic states are concerned. In addition, the role of projectile and multiphonon couplings in the enhancement has been explored.

Breakup and n -transfer effects on the fusion reactions Li6,7+Sn120,Fisichella1, Shotter2, Фігуера3 et al. 2017Phys. Rev. C20030View full textAdd to dashboardCite

“…For example, enhanced fusion cross sections have been observed for 28 Si + 94 Zr [10], 32 S + 96 Zr, 110 Pd [11,12] and 40 Ca + 48 Ca, 96 Zr, 124,132 Sn [13][14][15][16] systems compared to their isotopic counterparts characterized by lower Q values for neutron transfer. However, the fusion excitation functions for systems like Sn+Ni, Te+Ni [17], O+Ge [18], and Ni+Mo [19] do not show significant differences, when different isotopes of the colliding nuclei are considered, even though the systems present very different Q values for multineutron transfer channels.…”

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

“…The fusion cross-sections were calculated using the yield of evaporation residues (ERs) which were separated from the beam-like particles at the focal plane using energy loss in MWPC versus time of flight (TOF) spectrum [5]. For the cross-section calculations, transmission efficiency of HIRA was estimated experimentally by gamma ray coincidence technique [5] and it was found to be 7.8% at 130 MeV laboratory energy. It was also calculated as 7.6% using Monte-Carlo code TERS [19].…”

“…It was pointed out that strong transfer couplings may be the reason for this observation. Beside these observations, the importance of multi-neutron transfer on sub-barrier fusion was also indicated in an article [5].…”

“…The influence of transfer on fusion was noticed in systems having a positive Q-value for neutron transfer channels [3][4][5][6][7][8][9]. 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].…”

Sub-barrier fusion enhancement with radioactive134Te

“…A variety of experimental measurements have shown strong correlations between the presence of positive Q-value neutron transfer (PQNT) channels and enhanced sub-barrier fusion probabilities (see Refs. [1,[10][11][12][13][14][15][16][17][18][19][20] and references therein). For example, the fusion of the symmetric 40 Ca+ 40 Ca and 48 Ca+ 48 Ca systems show very similar excitation functions when taking into account the differences in the barrier height and nuclear radii.…”