Spectroscopy of ${}^{25}\mathrm{Ne}$ and the $N=16$ magic number

The low-energy level structure of ${}^{25}\mathrm{Ne}$ has been investigated following the ${\beta }^{-}$ decay of ${}^{25}\mathrm{F}$. Beta-delayed γ spectroscopy revealed new γ transitions in ${}^{25}\mathrm{Ne}$ at 1234, 1622, and 2090 keV. The new transitions were placed in the level scheme of ${}^{25}\mathrm{Ne}$ in accordance with the observed $\gamma \text{−}\gamma$ coincidences. The total ${\beta }^{-}$ decay strength has been accounted for. The spins and parities of the first two excited states could be ascertained by comparison with a shell model calculation and the literature. The half-life for ${}^{25}\mathrm{F}$ decay was also remeasured using fragment-$\beta \text{−}\gamma$ correlations, revealing a value of 90 ± 9 ms. Comparison with shell model calculations are indicative of a wider $N=16$ gap as compared to the stable nuclei.

Figure 1

(Color online) Time of flight vs dE particle identification plot used to differentiate the different nuclides reaching the DSSD.

Figure 2

(Color online) The decay curve for ${}^{25}\mathrm{F}$. Shown are the total fit to the decay curve, which includes the parent decay, daughter growth and decay, and the background along with the individual components. The half-life obtained for the decay of ${}^{25}\mathrm{F}$ is 112 ± 5 ms.

Figure 3

(Color online) The decay curve for ${}^{25}\mathrm{F}$ in coincidence with the 574- and the 1702-keV transitions in ${}^{25}\mathrm{Ne}$. A constant background was assumed in both cases.

Figure 4

β-delayed γ spectrum from events coming within 500 ms of a ${}^{25}\mathrm{F}$ implant. Gamma transitions from ${}^{25}\mathrm{Ne}$ are shown, including the new transitions at 1234, 1622, and 2090 keV. The 90-keV γ transition is from ${}^{25}\mathrm{Na}$; the 1982-keV one is from ${}^{24}\mathrm{Ne}$ formed by $\beta \text{−}n$ decay.

Figure 5

The fragment-$\beta \text{−}\gamma \text{−}\gamma$ coincidences observed from gating on γ transitions in ${}^{25}\mathrm{Ne}$.

Figure 6

Proposed level scheme for ${}^{25}\mathrm{Ne}$ obtained from the ${\beta }^{-}$ decay of ${}^{25}\mathrm{F}$ to the various energy levels in ${}^{25}\mathrm{Ne}$. The β-decay branchings are shown with the log ft values for each level on the left; the USD shell model calculations are shown on the right. The tentative spin and parity assignments to the excited states are also indicated.

Figure 7

Comparison of (i) ${}^{25}\mathrm{Ne}$ levels from the USD shell model [19] (all states have positive parity), (ii) level scheme from the present work, (iii) partial level scheme from the previous β-decay study [9], and energy levels identified in transfer reactions: (iv) (${}^7\mathrm{Li}$,${}^8\mathrm{F}$) [10], (v) (${}^{13}\mathrm{C}$,${}^{14}\mathrm{O}$) [11], (vi) one-neutron knockout from ${}^{26}\mathrm{Ne}$ [8], and (vii) one-neutron pickup ${}^{24}\mathrm{Ne}$($d,p$)${}^{25}$ [12].