Level structure of ${}^{26}\mathrm{Si}$ and its implications for the astrophysical reaction rate of ${}^{25}\mathrm{Al}$($p$,γ)${}^{26}\mathrm{Si}$

A study of the level structure of ${}^{26}\mathrm{Si}$ using in-beam γ-ray spectroscopy is presented. A full level scheme is derived incorporating all states lying below the proton threshold energy. The results are in good agreement with shell model predictions and one-to-one correspondence is found with states in the mirror nucleus ${}^{26}\mathrm{Mg}$. Additionally, a γ-decay branch is observed from a state at 5677.0(17) keV, which is assigned to a $1^{+}$ resonance important in the astrophysical reaction ${}^{25}\mathrm{Al}$($p$,γ)${}^{26}\mathrm{Si}$. The newly derived resonance energy, $E_r=159.2(35)$ keV, has the effect of decreasing the reaction rate at the novae ignition temperature of $\approx 0.1$ GK by a factor of $\approx 2$ when compared with the previous most precise measurement of this state.

Figure 1

Gamma-ray spectrum measured in coincidence with ${}^{26}\mathrm{Si}$ residues. The inset contains the high-energy γ rays detected in coincidence with the 1797 keV, $2_1^{+}\to 0_1^{+}$ transition.

Figure 2

The γ-decay scheme of ${}^{26}\mathrm{Si}$ obtained in this work.

Figure 3

Comparison between the ${}^{26}\mathrm{Si}$ levels, the states in ${}^{26}\mathrm{Mg}$, and the results of shell-model calculations [7].