Studies on Some Low-Lying Levels ofNe21

The ${\mathrm{Ne}}^{21}$ states below an excitation energy of 5 MeV have been studied via the ${\mathrm{Ne}}^{20}(d, p){\mathrm{Ne}}^{21}$ and ${\mathrm{Ne}}^{20}(d, p\gamma ){\mathrm{Ne}}^{21}$ reactions with deuteron bombardment energies below 4 MeV. Angular-distribution measurements performed on the unresolved proton groups corresponding to formation of the 2.790- and 2.797-MeV ${\mathrm{Ne}}^{21}$ states display $l_n=0\mathrm{}$ stripping characteristics. Based on the observed relative intensities of population for these two states in previous studies, this measurement is interpreted as direct evidence for a $J^{\pi }={\frac{1}{2}}^{+}$ assignment to the 2.797-MeV ${\mathrm{Ne}}^{21}$ state. Two-parameter proton-gamma time-coincidence measurements have been carried out to investigate the de-excitation branching ratios for the 1.75-, 2.87-, 3.67-, 3.74-, 3.89-, 4.53-, and 4.73-MeV ${\mathrm{Ne}}^{21}$ states. Proton-gamma angular-correlation studies were performed in a colinear geometry at $E_d=3.0\mathrm{}$ MeV. The results confirm previous $J=\frac{7}{2}$ determinations for the 1.75-MeV ${\mathrm{Ne}}^{21}$ state and indicate a value $x=+(0.11\mathrm{}\pm 0.03)$ for the multipole amplitude ratio of the 1.75→0.350 transition. They also indicate $J=\frac{3}{2} or \frac{5}{2}$ for both the 3.67- and 3.74-MeV states and $J\ge \frac{3}{2}$ for the 3.89-MeV state. All radiations originating from the 2.790-MeV state appeared isotropic within experimental uncertainties, and the present results indicate only that $J\le \frac{5}{2}$ for this state. The results of these and previous studies are compared with existing collective-model predictions concerning the ${\mathrm{Ne}}^{21}$ nuclear system.