Higher-spin structures in ${}^{21}\mathrm{F}$ and ${}^{25}\mathrm{Na}$

Excited states were investigated in ${}^{21}\mathrm{F}$ and ${}^{25}\mathrm{Na}$ using the ${}^9\mathrm{Be}\left({}^{14}\mathrm{C},pn\gamma \right)$ reaction at 30, 35, and 45 MeV and the ${}^9\mathrm{Be}\left({}^{18}\mathrm{O},pn\gamma \right)$ reaction at 35 MeV. Protons were detected and identified in an $E-\mathrm{\Delta }E$ telescope at $0^{\circ }$ in coincidence with one or more $\gamma$ radiations in the FSU Compton-suppressed Ge detector array. Many new levels and electromagnetic decays were observed, especially among the higher spin states. Angular distributions and mean lifetimes were measured wherever possible in both nuclei. The energy levels of the positive-parity states in the two nuclei agree rather well with shell model calculations using both the USDA and WBP interactions up to the highest spins observed of $13/2\hslash$. Both a weak coupling approximation and shell model calculations using the WBP interaction generally reproduce the negative-parity states in ${}^{21}\mathrm{F}$. The shell model calculations reproduce relatively well the measured $M1$ and $E2$ transitions in both nuclei, but overpredict the parity-changing $E1$ transitions in ${}^{21}\mathrm{F}$, the only nucleus in which negative-parity states were observed in the present experiment.

Figure 1

The level and decay scheme of ${}^{25}\mathrm{Na}$ based on the present data. States and transitions in red are new to this work; transition widths are proportional to the observed intensities.

Figure 2

Portions of the $\gamma$ spectra in coincidence with the 2419 and 2790 (inset) keV lines. Red labels are used for newly observed $\gamma$ peaks.

Figure 3

Portions of gated $\gamma$ spectra around the energies of previously reported decays of the 3995 $1/2^{-}$ state in ${}^{25}\mathrm{Na}$.

Figure 4

Some sample DSAM lineshapes and fits for transitions in ${}^{25}\mathrm{Na}$. The black curves represent the best overall fits, while the red and blue curves indicate the one standard deviation uncertainties.

Figure 5

The level and decay scheme of ${}^{21}\mathrm{F}$ based on the present data. States and transitions in red are new to this work; transition widths are proportional to the observed intensities.

Figure 6

A portion of the $\gamma$ spectrum in coincidence with the 1755 keV line in ${}^{21}\mathrm{F}$.

Figure 7

A portion of the $\gamma$ spectrum in coincidence with the 2068 keV line in ${}^{21}\mathrm{F}$. Analysis of the uncompressed spectrum shows that about 1/3 of the 1983 keV peak comes from ${}^{21}\mathrm{F}$.

Figure 8

Some sample DSAM lineshapes and fits for transitions in ${}^{21}\mathrm{F}$. The black curves represent the best overall fits, while the red and blue curves indicate the one-standard-deviation uncertainties.

Figure 9

Comparison of lower experimental energy levels in ${}^{21}\mathrm{F}$ with two shell model calculations using the indicated interactions. Partially model-dependent spin assignments are shown in parentheses and newly reported energy levels are colored red.

Figure 10

Comparison of higher experimental energy levels in ${}^{21}\mathrm{F}$ with two shell model calculations using the indicated interactions. Partially model-dependent spin assignments are shown in parentheses and newly reported energy levels are colored red.

Figure 11

Comparison of lowest excited states in ${}^{22}\mathrm{Ne}$ with negative-parity states in ${}^{21}\mathrm{F}$ and $1p-1h$ shell model calculations using the WBP interaction. The levels in ${}^{22}\mathrm{Ne}$ are color-coded to match the corresponding states in experiment and the WBP shell-model calculations.

Figure 12

Comparison of experimental energies levels in ${}^{25}\mathrm{Na}$ with two shell model calculations using the indicated interactions. Partially model-dependent spin assignments are shown in parentheses and newly reported energy levels are colored red.

Figure 13

Comparison of lowest excited states in ${}^{26}\mathrm{Mg}$ with negative-parity states in ${}^{25}\mathrm{Na}$ reported in the literature and $1p-1h$ shell model calculations using the WBP interaction. The levels in ${}^{26}\mathrm{Mg}$ are color-coded to match the corresponding states in experiment and the WBP shell-model calculations.