One-neutron knockout in the vicinity of the $N=32$ sub-shell closure: ${}^9\mathrm{Be}$(${}^{57}\mathrm{Cr}$,${}^{56}\mathrm{Cr}$+γ)X

The one-neutron knockout reaction ${}^9\mathrm{Be}$(${}^{57}\mathrm{Cr}$,${}^{56}\mathrm{Cr}$+γ)X has been measured in inverse kinematics with an intermediate-energy beam. Cross sections to individual states in ${}^{56}\mathrm{Cr}$ were partially untangled through the detection of the characteristic γ-ray transitions in coincidence with the reaction residues. The experimental inclusive longitudinal momentum distribution and the yields to individual states are compared to calculations that combine spectroscopic factors from the full $\mathit{fp}$ shell model and nucleon-removal cross sections computed in a few-body eikonal approach.

Figure 1

Energy loss vs TOF particle identification spectra for the one-neutron knockout reaction setting and the unreacted incoming beam. Right: incoming, unreacted cocktail beam passing through the ${}^9\mathrm{Be}$ target. This unreacted setting was used to determine normalization of the incoming rate of ${}^{57}\mathrm{Cr}$. Left: spectrum obtained with the one-neutron removal reaction residues centered in the S800 focal plane. A software gate was applied on incoming ${}^{55}\mathrm{V}$ and ${}^{57}\mathrm{Cr}$ in the TOF difference measured between two plastic scintillators before the target.

Figure 2

γ-ray spectrum detected in coincidence with ${}^{56}\mathrm{Cr}$ knockout residues. Observed transitions agree with the level scheme established in [10, 11]. Population of individual excited states in the knockout reaction is derived from γ-ray intensities relative to the number of knockout residues, taking the level scheme into account. The fraction of 2.6% for the knockout to the ground state is obtained after subtraction.

Figure 3

Schematic shell-model level scheme, configurations, and resulting theoretical cross sections for the population of excited states in ${}^{56}\mathrm{Cr}$. The shell-model calculation is schematic. Cross sections are calculated from eikonal reaction theory as described in the text (Table ).

Figure 4

Inclusive parallel momentum distribution of the ${}^{56}\mathrm{Cr}$ knockout residues compared with theoretical results (solid red line) calculated using the eikonal stripping reaction mechanism. Weights attributed to knockout contributions from $2p_{3/2},1f_{5/2},2p_{1/2}$, and $1f_{7/2}$ orbits were taken from the corresponding theoretical cross sections (Table ). The dashed blue line is the momentum profile of the unreacted ${}^{57}\mathrm{Cr}$ projectile beam passing through the target.