Extracting Neutron Spectroscopic Factors From 34Ar(p,d)33Ar and 46Ar(p,d)45Ar

Juan Manfredi, Michigan State University

Photo of Juan Manfredi

The nuclear shell model describes the nucleus in terms of energy levels occupied individually by the constituent protons and neutrons. In the simplest model, called the Independent Particle Model (IPM), these nucleons occupy individual single-particle states in a mean field. Spectroscopic factors (SFs) quantify the single-particle nature of states in a nucleus.

A recent interesting puzzle in nuclear physics is the quenching of the SF observed in knockout reactions. SFs extracted from a recent knockout experiment indicate that the agreement of SFs with shell model predictions is reduced for proton-rich nuclei relative to neutron-rich nuclei. But the SFs for the same systems extracted from transfer reaction (where a nucleon is transferred to another nucleus) data suggest that agreement with the shell model stays relatively constant across the nuclear landscape.

To provide better understanding of this mystery, we measured (p,d) reactions for 34Ar (Z=18, N=16, where strong quenching was seen in knockout reactions) and 46Ar (Z=18 and N=28, where no quenching was seen) at the same beam energy (70 MeV) as the knockout measurements. The experiment was done at the National Superconducting Cyclotron Laboratory at Michigan State University using the High Resolution Array (HiRA). HiRA is a modular array of position-sensitive silicon detectors and CsI scintillators that provides energy, angle and particle identification. The results of the SF analysis will be compared to the previous experiment done at a lower beam energy (E/A = 35 MeV) and to the knockout results. Ultimately, the goal of this effort is to resolve this controversy between transfer and knockout results in order to properly quantify how nuclear shell structure evolves from proton-rich to neutron-rich nuclei.

Abstract Author(s): Juan Manfredi on behalf of the HiRA collaboration