NewP30(p,γ)

Abstract

Enriched isotopic abundance ratios of 30 Si/ 28 Si in several presolar SiC and graphite grains qualitatively indicate massive oxygen-neon (ONe) nova origins but fall short of hydrodynamic ONe nova model ejecta predictions by as much as an order of magnitude. The astrophysical 30 P(p, γ ) 31 S reaction rate uncertainty at ONe nova temperatures (0.10 < T < 0.35 GK) spans several orders of magnitude through which the predicted amount of ejected 30 Si can vary by a factor of 100. By measuring triton momenta from the 31 P( 3 He,t) 31 S reaction at 20 MeV, the energies of 30 P +p resonances in the Gamow window for ONe novae have been determined to better than ±3 keV, and two new resonances at E c.m. = 194.0(25) and 266.4(27) keV that likely dominate the 30 P(p, γ ) 31 S rate for 0.08 < T < 0.25 GK have been resolved. A resulting increase in the experimentally determined 30 P(p, γ ) 31 S reaction rate puts it in accord with Hauser-Feshbach statistical model estimates for 0.08 < T < 0.40 GK, supporting conclusions drawn from ONe nova model studies that employed a Hauser-Feshbach rate.

Toward concordance of $E_{x}$ and $J^{\pi}$ values for proton unbound 31S states

“…This peak could, in principle, consist of non-negligible contributions from 3 different unresolved levels claimed to exist in the range of E x ≈ 6390 to 6405 keV [14,17,22] [11]), and a third state of unknown spin/parity in the vicinity of 6400 keV [5,14,15,18]. The fact that the 31 P( 3 He,t) 31 S peak position is not consistent with either of the excitation energies 6392.5(2) keV or 6394.2(2) keV reported in Doherty et al appears to be further evidence for the population of the ≈ 6400 keV level, which is needed to shift the centroid of the single 31 P( 3 He,t) 31 S peak assumed here to positions corresponding to significantly higher excitation energies.…”

“…Refs. [14,5,18] all observed two levels at about 6394 and 6402 keV; ref. [17] also observed two levels in this energy region, but at 6393 and 6394 keV.…”

“…As such, estimates of rates based upon the available experimental information [4,5,13,15,17,19] suffer from uncertainties that are difficult to quantify. In the present work we use published data from measurements of the 31 P( 3 He,t) 31 S [5,14,15] and 32 S(d,t) 31 S [20] reactions to address discrepancies in E x (see sects. 2 and 3, respectively) and J π values (see sect.…”

“…Indirect methods must therefore be exploited: nuclear structure information is required for states within ≈ 600 keV of the 30 P+p threshold in 31 S. In particular, excitation energies E x , J π values, proton and γ-ray partial widths, proton-transfer spectroscopic factors, and total widths of these levels are needed to estimate the 30 P(p, γ) 31 S rate. There has been significant recent activity concentrated on determining the structure of proton unbound states in 31 S [4,5,10,[12][13][14][15][16][17][18]. Unfortunately, discrepancies exist for both E x and J π values of states in the energy region of interest.…”

Asymptotic normalization of mirror states and the effect of couplings

“…[4]). In many cases, the capture process occurs through specific resonances which need to be well known [5]. However, even in these cases, it is important to understand the role of direct capture.…”