Study of 28,27,26,25Ne and 29,28,27Na Isotopes via the Single Neutron Knockout Reaction Mechanism.

An investigation aimed at measuring the structural changes in the ground state structure of the 28-25Ne and 29-27Na isotopes has been conducted using the single neutron knockout reaction. The EXOGAM array and the SPEG spectrometer were used to measure γ-rays in coincidence with residual core fragments from the knockout reaction product. In each of the 27,26,25Ne nuclei, excited states have been identified. For certain states exclusive momentum distributions in coincidence with γ-rays support the spin assignment. Also, transitions in the 28,27,26Na nuclei were recorded, including some γ-ray transitions which are not currently published. For each of the 27,26,25Ne and 28,27,26Na nuclei, γ-ray intensities relative to the number of knockout reaction products have been measured. Balancing of these intensities using level schemes inferred from results in this work, published work, and with guidance from the shell model, allow for the population to individual states in the residual core nucleus (referred to as “branches”) to be deduced. These branches have also been calculated using the USD, USDA and USDB shell model interactions for comparison. It has been found that the shell model incorrectly predicts the branches linking the 27,25Ne projectiles and their respective single neutron knockout core excited states, whilst the 26Ne results are qualitatively in better agreement with the shell model. It is proposed in some instances that the shell model may predict too much pair excitation of neutrons into the d3/2 orbital. The data from 29,28Na projectiles have been compared with the shell model using the experimental and theoretical inclusive momentum distributions. Exclusive momentum distributions for the sodiums were not obtained because of the uncertainty in sodium level schemes, and the high density of transitions which make it difficult to extract distributions. The observed widths and shapes of the theoretically calculated distributions were in good agreement with experiment, indicating that the shell model predicts the s and d-wave neutron removal from the 29,28Na ground states approximately correctly. The comparison of the 27Na projectile with theory shows slightly poorer agreement with theory, where the shell model indicates too much d-wave neutron removal. It has been proposed that the shell model may again overestimate the degree of neutron pair excitation into the d3/2 orbital, and that some of the neutron occupancy in the 27Na ground state should more correctly reside in the s 1/2 orbital