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Study of pairing correlations

In mean field calculations, the pairing interaction is largely unconstrained, whereas its nature (force, volume/surface) is determinative in the evolution, for example, of neutron stars. At SPIRAL2, pair transfer reactions such as (p,t) and (t,p) with inverse kinematics will be implemented for neutron-rich nuclei such as 132-136Sn. In this approach, the interesting observables are the angular distributions and the effective cross-section ratios of states 0+ (fundamental and lower states). Theoretical work inside the IPN (see Figure 1) has already begun in order to test the sensitivity of these observables to different pairing interactions. By 2015, this methodology will be testable using stable beams like the proton beams of the IPN Tandem.

Figure 1. Top graph : density profiles of isotopes 124Sn and 136Sn. Bottom graph : pairing field profiles for the 124Sn nucleus evaluated with a surface interaction and with a mixed volume/surface interaction (Hartree-Fock-Bogoliubov calculations)

Neutron-proton pairing, which has not received much experimental study so far, is especially interesting because unlike the pairing of identical nucleons, it can take place not only in isospin channel T=1 but also in T=0. This type of pairing is expected in radioactive N=Z nuclei with high orbital angular momentum. It can be studied by deuton transfer reaction using beams generated by GANIL’s LISE spectrometer and the MUST2 particle detector. An initial experiment with 56Ni and 48Cr beams will be taking place soon and this programme can continue in the future with heavier N=Z nuclei.



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