Spectroscopic Factor Investigation in the N=40 Island of Inversion*

The focus of this work is on the Fe and Mn neutron-rich isotopes with N~40, which lie within one of the so-called Islands of Inversion. Here, a quenching of the N=40 shell gap allows deformation to develop in the ground-state configurations. Limited spectroscopic information is available in the region of N~40 below the Ni isotopes. For the even-even nuclei, this consists of systematics of 2⁺₁ and 4⁺₁ state energies and, for the Fe and Cr isotopes, of B(E2; 2⁺₁→0⁺₁) values up to ⁶⁸Fe and ⁶⁴Cr. Large-scale shell model calculations well reproduce the energy systematics of the observed low-lying states of the even-even Fe and Cr isotopes around N=40. A good agreement is found also within the rotational Nilsson model. Such two descriptions, however, provide different predictions for proton spectroscopic factors. A measurement of such quantity would thus allow us to probe the validity of the considered models.

In this context, proton knockout reactions on the neutron-rich N=38 and N=40 isotopes ^64,66Fe and ^63,65Mn have been performed to investigate the proton spectroscopic factors of the parent nuclei. The experiment took place at the NSCL laboratory in the US and exploited the ??-ray tracking array GRETINA coupled to the S800 spectrograph to perform an in-beam ??-ray spectroscopic study. Preliminary results of the data analysis will be presented.