Evolution of the neutron 1d3/2-1d5/2 spin-orbit splitting in N=19 isotones and Fermi surface in 34Si

The e869_22 experiment aims to probe the neutron magicity at N=20 in 34Si by determining whether the f and p valence orbitals located above the N=20 gap are populated or not; and to determine the evolution of the d5/2–d3/2 splitting between the nuclei 34Si, 36S, and 40Ca, in order to better understand the role of spin–orbit and tensor components of the nuclear force.

The neutron orbitals of this nucleus are populated via the (p,d) reaction, which transfers a neutron from a radioactive 34Si projectile. This projectile is produced by fragmentation and selected in flight at 50 MeV/u using the LISE spectrometer, and it interacts with the protons of a CH2 target of 5 mg/cm2, placed within the CATS–MUST2–EXOGAM2–ZDD setup. The removal of a neutron from 34Si and the characterization of the neutron orbitals of the residual nucleus 33Si are carried out by studying the energy and emission angle of the deuterons emitted at forward angles, using the MUST2 array of charged-particle detectors, in coincidence with the detection of the residual 33Si nuclei in the ZDD identification chamber at 0°.

When the 33Si nucleus is populated in an excited state, it is characterized in energy through its gamma decay, detected by EXOGAM2. The CATS trackers placed upstream of the target allow for Doppler correction of the detected gamma-ray energies and, more generally, for monitoring the kinematic parameters of the observed reactions.

For the purpose of calibrating the experimental setup and validating the data analysis protocol, the same (p,d) reactions were also performed using the stable primary beam of 36S, leading to the production of 35S.