First direct limit on the 334 keV resonance strength in $$^{22}$$Ne($$\alpha $$,$$\gamma $$)$$^{26}$$Mg reaction

Abstract

In stars, the fusion of $$^{22}$$ 22 Ne and $$^4$$ 4 He may produce either $$^{25}$$ 25 Mg, with the emission of a neutron, or $$^{26}$$ 26 Mg and a $$\gamma $$ γ ray. At high temperature, the ($$\alpha ,n$$ α , n ) channel dominates, while at low temperature, it is energetically hampered. The rate of its competitor, the $$^{22}$$ 22 Ne($$\alpha $$ α ,$$\gamma $$ γ )$$^{26}$$ 26 Mg reaction, and, hence, the minimum temperature for the ($$\alpha ,n$$ α , n ) dominance, are controlled by many nuclear resonances. The strengths of these resonances have hitherto been studied only indirectly. The present work aims to directly measure the total strength of the resonance at $$E_{\text {r}}$$ E r = 334 keV (corresponding to $$E_{\text {x}}$$ E x = 10949 keV in $$^{26}$$ 26 Mg). The data reported here have been obtained using high intensity $$^4$$ 4 He$$^+$$ + beam from the INFN LUNA 400 kV underground accelerator, a windowless, recirculating, 99.9% isotopically enriched $$^{22}$$ 22 Ne gas target, and a 4$$\pi $$ π bismuth germanate summing $$\gamma $$ γ -ray detector. The ultra-low background rate of less than 0.5 counts/day was determined using 63 days of no-beam data and 7 days of $$^4$$ 4 He$$^+$$ + beam on an inert argon target. The new high-sensitivity setup allowed to determine the first direct upper limit of 4.0$$\,\times \,$$ × 10$$^{-11}$$ - 11 eV (at 90% confidence level) for the resonance strength. Finally, the sensitivity of this setup paves the way to study further $$^{22}$$ 22 Ne($$\alpha $$ α ,$$\gamma $$ γ )$$^{26}$$ 26 Mg resonances at higher energy.

Advances in radiative capture studies at LUNA with a segmented BGO detector

“…Setup, data acquisition and analysis techniques evolved continuously throughout the decades with this detector, further pushing the limits of experimental sensitivity. The work presented here is a continuation of the efforts 15 O [15] 7297 Gas None 25 Mg(p,γ) 26 Al [17] 6306 A-solid None 18 O(p,γ) 19 F [28] 7994 A-solid Pb 23 Na(p,γ) 24 Mg [27] 11 693 A-solid Pb 22 Ne(p,γ) 23 Na [50] 8794 Gas None 22 Ne(α,γ) 26 Mg [19] 10 615 Gas BPE (10 cm) thick 12 C(p,γ) 13 reported in [20] and is guided by the background models presented in that work. Of the two beamlines at LUNA-400 we will here focus on the solid target setup.…”

“…res. = 334 keV resonance in 22 Ne(α,γ) 26 Mg, with a sensitivity that allowed to establish an upper limit for its ωγ of 4.0 × 10 −11 eV [19]. Setup, data acquisition and analysis techniques evolved continuously throughout the decades with this detector, further pushing the limits of experimental sensitivity.…”

Towards a direct measurement of the 17O(p, γ)18F 65 keV resonance strength at LUNA

“…4 and the net counts, calculated subtracting from the 17 O counts the background counts observed in the UPW spectra, were far above the critical limit. The resonance strength was derived in a monte carlo based approach [19][20][21]. The background and the signal, observed in the same ROI but in UPW and 17 O + p spectra respectively, were assumed to follow a Poisson distribution, and 10 6 samples were taken for each.…”

The resonances in the $$^{22}$$Ne+$$\alpha $$ fusion reactions

“…Thus a substantially increased rate is obtained at these lower temperatures. A recent attempt of the LUNA collaboration [50] to directly measure the resonance strength yielded an experimental upper limit for the resonance strength, which however, would translate into a α spectroscopic factor, which is much larger than the allowed by the Wigner limit. The reaction rate is compared to that of [29] in Fig.…”