Deeply-bound nucleon removal and transfer from light exotic nuclei

Wednesday 2 November 2011, 1.15PM

Speaker(s): Dr Alexandre Obertelli, CEA, France


The distribution of spectroscopic strength in nuclei can be extracted from direct-reaction cross section measurements, assuming a proper modelling of the reaction mechanism. Direct transfer or knockout reactions in inverse kinematics, at low and intermediate energies respectively, are essential tools to study the shell structure of unstable nuclei.
Recently, a compilation of one-nucleon removal at intermediate energies from sd-shell exotic nuclei showed that the measured cross sections of knocking out a deeply-bound nucleon (namely a neutron in 32Ar, 28Ar and 24Si) are about four times smaller than predictions from state-of-the-art calculations [1]. On the other hand, at low energy, a study of the (p,d) neutron transfer on the proton-rich 34Ar and on the neutron-rich 42Ar provides experimental spectroscopic factors in agreement to within 20% with large-basis shell model calculations [2]. These findings which are in agreement with a previous systematic study of transfer reactions [3] are inconsistent with the trend observed in knockout. Therefore, it is suggested that these two probes lead systematically to different spectroscopic factors. The origin of this difference has to be understood.
To further investigate this question, we performed one-nucleon removal on 14O and 16C at the NSCL at 53 and 75 MeV/nucleon respectively. Both have a large difference of proton and neutron separation energies, of about 20 MeV, similar to the cases where a strong discrepancy  between knockout measurements and theoretical cross section predictions were observed. Moreover, in order to have a complete description of a same proton-rich nucleus both in knockout and transfer, we also studied 14O via the one-nucleon transfer reactions 14O(d,t)13O and 14O(d,3He)13N at 18 MeV/nucleon at GANIL. The results of both experiments will be presented and compared.
Recent theoretical investigations on the reliability of approximations usually considered in the eikonal formalism will also be discussed [4,5].
[1] A. Gade et al. , Phys. Rev. C 77, 044306 (2008).
[2] J. Lee et al. , Phys. Rev. Lett. 104, 112701 (2010).
[3] M. B. Tsang et al. , Phys. Rev. Lett. 102, 062501 (2009).
[4] F. Flavigny et al., Phys. Rev. C 79, 064617 (2009).
[5] C. Louchart et al., Phys. Rev. C 83, 011601(R) (2011).

Location: P/T103