Fusion Hindrance and Pauli Blocking in 58 Ni + 64 Ni

• Published in: EPJ Web of conferences Vol. 223; p. 1062
• Main Authors: Stefanini, Alberto M., Montagnoli, Giovanna, Del Fabbro, Mirco, Colucci, Giulia, Čolović, Petra, Corradi, Lorenzo, Fioretto, Enrico, Galtarossa, Franco, Goasduff, Alain, Grebosz, Jerzy, Heine, Marcel, Jaworski, Grzegorz, Mazzocco, Marco, Mijatović, Tea, Szilner, Suzana, Bajzek, Martin, Brugnara, Daniele, Siciliano, Marco, Zanon, Irene
• Format: Journal Article
• Language: English
• Published: 2019
• ISSN: 2100-014X; 2100-014X
• DOI: 10.1051/epjconf/201922301062

58
Ni +
64
Ni is the first case where the influence of positive Q-value transfer channels on sub-barrier fusion was evidenced, in a very well known experiment by Beckerman et al., by comparing with the two systems
58
Ni +
58
Ni and
64
Ni+
64
Ni. Subsequent measurements on
64
Ni +
64
Ni showed that fusion hindrance is clearly present in this case. On the other hand, no indication of hindrance can be observed for
58
Ni +
64
Ni down to the measured level of 0.1 mb. In the present experiment the excitation function has been extended by two orders of magnitude downward. The cross sections for
58
Ni + 64Ni continue decreasing very smoothly below the barrier, down to '1 µb. The logarithmic slope of the excitation function increases slowly, showing a tendency to saturate at the lowest energies. No maximum of the astrophysical
S
-factor is observed. Coupled-channels (CC) calculations using a Woods-Saxon potential and includinginelastic excitations only, underestimate the sub-barrier cross sections by a large amount. Good agreement is found by adding two-neutron transfer couplings to a schematical level. This behaviour is quite different from what already observed for
64
Ni+
64
Ni (no positive
Q
-value transfer channels available), where a clear low-energy maximum of the
S
-factorappears, and whose excitation function is overestimated by a standard Woods-Saxon CC calculation. No hindrance effect is observed in
58
Ni+
64
Ni in the measured energy range. This trend at deep sub-barrier energies reinforces the recent suggestion that the availability of several states following transfer with
Q
>0, effectively counterbalances the Pauli repulsion that, in general, is predicted to reduce tunneling probability inside the Coulomb barrier.