Neutron-proton pairing in the N=Z radioactive fp-shell nuclei $^{56}$Ni and $^{52}$Fe probed by pair transfer

B. Le Crom (1) , M. Assié (1) , Y. Blumenfeld (1) , J. Guillot (1) , H. Sagawa , T. Suzuki , M. Honma , N.L. Achouri (2) , B. Bastin (2) , R. Borcea , W.N. Catford , E. Clément (3) , L. Caceres (3) , M. Caamano , A. Corsi (4) , G. de France (3) , F. Delaunay (2) , N. de Séréville (1) , B. Fernandez-Dominguez , M. Fisichella , S. Franchoo (1) , A. Georgiadou (1) , J. Gibelin (2) , A. Gillibert (4) , F. Hammache (1) , O. Kamalou (3) , A. Knapton , V. Lapoux (4) , S. Leblond (2) , A.O. Macchiavelli , F.M. Marques (2) , A. Matta (2) , L. Menager (3) , P. Morfouace (1) , N.A. Orr (2) , J. Pancin (3) , X. Pereira-Lopez (2) , L. Perrot (1) , J. Piot (3) , E. Pollacco (4) , D. Ramos , T. Roger (3) , F. Rotaru , A.M. Sanchez-Benitez , M. Sénoville (4) , O. Sorlin (3) , M. Stanoiu , I. Stefan (1) , C. Stodel (3) , D. Suzuki (1) , J-C Thomas (3) , M. Vandebrouck (3)

1 IJCLab - Laboratoire de Physique des 2 Infinis Irène Joliot-Curie
2 LPCC - Laboratoire de physique corpusculaire de Caen
3 GANIL - Grand Accélérateur National d'Ions Lourds
4 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers

The isovector and isoscalar components of neutron-proton pairing are investigated in the N=Z unstable nuclei of the fp-shell through the two-nucleon transfer reaction (p,³He) in inverse kinematics. The combination of particle and gamma-ray detection with radioactive beams of ⁵⁶Ni and ⁵²Fe, produced by fragmentation at the GANIL/LISE facility, made it possible to carry out this study for the first time in a closed and an open-shell nucleus in the fp-shell. The transfer cross-sections for ground-state to ground-state (J=0⁺, T=1) and to the first (J=1⁺, T=0) state were extracted for both cases together with the transfer cross-section ratios $\sigma (0^{+},\text{T=1})/\sigma (1^{+},\text{T=0})$. They are compared with second-order distorted-wave born approximation (DWBA) calculations. The enhancement of the ground-state to ground-state pair transfer cross-section close to mid-shell, in ⁵²Fe, points towards a superfluid phase in the isovector channel. For the “deuteron-like” transfer, very low cross-sections to the first (J=1⁺, T=0) state were observed both for ⁵⁶Ni(p,³He) and ⁵²Fe(p,³He) and are related to a strong hindrance of this channel due to spin-orbit effect. No evidence for an isoscalar deuteron-like condensate is observed.

Keywords: Radioactive beam; Direct reactions; Neutron-proton pairing; Cooper pairs

Domains: Nuclear Experiment [nucl-ex]

B. Le Crom, M. Assié, Y. Blumenfeld, J. Guillot, H. Sagawa, et al.. Neutron-proton pairing in the N=Z radioactive fp-shell nuclei $^{56}$Ni and $^{52}$Fe probed by pair transfer. Phys.Lett.B, 2022, 829, pp.137057. ⟨10.1016/j.physletb.2022.137057⟩. ⟨hal-03217631⟩