Destruction of the cosmic $\gamma$-ray emitter ${}^{26}\mathrm{Al}$ in massive stars: Study of the key ${}^{26}\mathrm{Al}(n,\alpha )$ reaction

Neutron destruction reactions of the cosmic $\gamma$-ray emitter ${}^{26}\mathrm{Al}$ are of importance to determine the amount of ${}^{26}\mathrm{Al}$ ejected into our galaxy by supernova explosions and for ${}^{26}\mathrm{Al}$ production in asymptotic giant branch stars. We performed a new measurement of the ${}^{26}\mathrm{Al}(n,\alpha )$ reaction up to 160-keV neutron energy at the neutron time-of-flight facilities n_TOF at CERN and GELINA at EC-JRC. We provide strengths for ten resonances, six of them for the first time. We use our data to calculate astrophysical reactivities for stellar temperatures up to 0.7 GK. Our results resolve a discrepancy between the two previous direct measurements of this reaction, and indicate higher stellar destruction rates than the most recently recommended reactivity.

Figure 1

(a) Count spectrum of the 5.9-keV resonance. (b) Count spectrum from 10 to 160 keV. Resonances listed in Table 1 are indicated by solid lines. The inset shows the count spectrum of the 35-keV resonance obtained at GELINA used for determining the resonance strength at 35 keV as the n_TOF neutron flux has a large absorption dip at that energy (see the text for details).

Figure 2

$\alpha$-energy spectrum measured in the $20\text{−}\mu \mathrm{m}$-thick SSD detectors for the ${}^{26}\mathrm{Al}(n,\alpha )$ resonance at 41.3-keV neutron energy recorded at the GELINA time-of-flight facility. The peaks around 2.4 and 2 MeV correspond to $(n,{\alpha }_0)$ and $(n,{\alpha }_1)$ events, respectively.

Figure 3

Stellar reactivities obtained in this Letter, and the contributions of the individual resonances and the unresolved region (URR).

Figure 4

Stellar reactivity compared to previous measurements and theoretical calculations. The results of this Letter are shown as a black band. These results are compared to experimental results by De Smet et al. [11, 23] and Koehler et al. [10], and theoretical and evaluated reactivities (non-smoker [21, 22], Oginni et al. [12]). See the text for details.