Abstract
.The 16.1 MeV 2^{+} resonance in 12C situated slightly above the proton threshold can decay by proton, alpha, and gamma emission. The partial width for proton emission cannot be directly measured due to the low proton energy and the small branching ratio. Instead it must be indirectly derived from other observables. However, due to several inconsistent data the derived partial width varies by almost a factor 2 depending on the data used. Here we trace the majority of this inconsistency to different measurements of the (p,alpha) cross sections. We have remeasured this cross section using modern large area silicon strip detectors allowing to measure all final state particles, which circumvents a normalization issue affecting some of the previous measurements. Based on this we determine Gamma_{p} = 21.0(13) eV. We discuss the implications for other observables related to the 16.1 MeV 2^{+} resonance and for isospin symmetry in the A = 12 system. In addition, we conclude that the dataset currently used for the NACRE and NACRE II evaluation of the 11B(p, 3alpha) reaction should be scaled by a factor of 2/3. This impacts the reaction rate accordingly.
Highlights
Situated just above the proton threshold, the 16.1 MeV2+ state in 12C has been the subject of numerous studies [1–14] with the most recent compilation published in ref. [15] and a detailed review of the decay properties of the 16.1 MeV state given in ref. [12]
We have remeasured this cross section using modern large area silicon strip detectors allowing to measure all final state particles, which circumvents a normalization issue affecting some of the previous measurements
The proton width recommended by ref. [15] results in good agreement with this spectroscopic factor, while that of ref. [12] does not
Summary
2+ state in 12C has been the subject of numerous studies [1–14] with the most recent compilation published in ref. [15] and a detailed review of the decay properties of the 16.1 MeV state given in ref. [12]. The decay properties of T = 1 isobaric analog states in the A = 12 system was analysed by Monahan et al [17] This analysis was based on a comparison of the proton widths in 12C with the neutron spectroscopic factors in 12B deduced from the 11B(d, p)12B reaction. There are multiple consistent measurements for the resonance width and combining the results from refs. All of the cross section measurements of the (p, α) channel were performed with a small energy sensitive detector placed at various angles. In this paper we will only address the cross section of the 16.1 MeV state, but the discussion on normalization applies universally to all measurements of this reaction, where the cross section is inferred from a single detector
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