New measurement of the $E_{\alpha }^{\mathrm{lab}}=0.83$ MeV resonance in ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$

The $E_{\alpha }^{\text{lab}}=0.83$ MeV resonance in the ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction strongly impacts the reaction rates in the stellar temperature region crucial for the astrophysical s process. We report on a new measurement of the energy and strength of this resonance using techniques different from previous investigations. We use a blister-resistant ${}^{22}\mathrm{Ne}$-implanted target and employ $\gamma \gamma$-coincidence detection techniques. We find values for the resonance energy and strength of $E_{\alpha }^{\text{lab}}=835.2\pm 3.0$ keV and $\omega \gamma =(4.6\pm 1.2)\times {10}^{-5}$ eV, respectively. Our mean values are higher compared to previous values, although the results overlap within uncertainties. The uncertainty in the resonance energy has been significantly reduced. The spin-parity assignment, based on the present and previous work, is $J^{\pi }=$ ($0^{+}$, $1^{-}$, $2^{+}$, $3^{-}$).

Figure 1

Yield curve for the $E_p^{\text{lab}}=479$ keV resonance in the ${}^{22}\mathrm{Ne}(p,\gamma ){}^{23}\mathrm{Na}$ reaction, after an accumulated $\alpha$-particle charge of 3.5 C. The $\gamma$ ray monitored for the yield had an energy of 6270 keV, corresponding to the 9252 $\to$ 2982-keV primary transition in ${}^{23}\mathrm{Na}$. The target thickness was about 19 keV for protons at this energy. The cyan-shaded region depicts the uncertainty in the fitted yield curve.

Figure 2

Selected parts of HPGe spectra, obtained with an $\alpha$-particle beam on a ${}^{22}\mathrm{Ne}$-implanted Ti backing. (Black histogram) Singles spectrum at $E_{\alpha }^{\text{lab}}=904$ keV (on-resonance), after a charge accumulation of 3.4 C; all peaks shown are caused by room background (${}^{40}\mathrm{K}$, ${}^{208}\mathrm{Tl}$, etc.). (Red histogram) $\gamma \gamma$-coincidence spectrum with muon veto applied, recorded at the same energy and with the same charge accumulation; the secondary $1809\to 0$ transition from the ${}^{22}\mathrm{Ne}(\alpha ,\gamma ){}^{26}\mathrm{Mg}$ reaction is clearly observed. (Blue histogram) $\gamma \gamma$-coincidence spectrum with muon veto applied, recorded at $E_{\alpha }^{\text{lab}}=815$ keV (off-resonance) and a charge accumulation of 1.4 C. No contributions have been subtracted from any of the spectra shown.

Figure 3

Selected parts of HPGe spectra, obtained with an $\alpha$-particle beam on a ${}^{22}\mathrm{Ne}$-implanted Ti backing. The bombarding energies for the red and blue histograms were $E_{\alpha }^{\text{lab}}=904$ keV (on resonance) and 815 keV (off resonance), respectively. The left panel shows $\gamma \gamma$-coincidence spectra, while the right panel displays singles spectra with the muon veto applied. The two labeled peaks correspond to the only primary transitions in ${}^{26}\mathrm{Mg}$ ($R\to 1809$ keV and $R\to 7062$ keV) observed during the experiment. No contributions have been subtracted from any of the spectra shown.