First Direct Measurement of Mg22(α,p)Al

Abstract

Type-I x-ray bursts can reveal the properties of an accreting neutron star system when compared with astrophysics model calculations. However, model results are sensitive to a handful of uncertain nuclear reaction rates, such as 22 Mgðα;pÞ. We report the first direct measurement of 22 Mgðα;pÞ, performed with the Active Target Time Projection Chamber. The corresponding astrophysical reaction rate is orders of magnitude larger than determined from a previous indirect measurement in a broad temperature range. Our new measurement suggests a less-compact neutron star in the source GS1826-24.

Proton decays from $α$-unbound states in $^{22}$Mg and the $^{18}$Ne($α, p_{0}$)$^{21}$Na cross section

“…Finally, we note that if we assume that the E x = 8.985(8)-MeV state and the broad E x = 9.029(7)-keV state are the same state, the present data support a stronger p 1 decay branch for this state compared to the p 0 branch. In this case, proton peaks at E x = 3152 (8) keV or E p = 3186 (7) keV (depending on the choice of energy for the initial state) should be observed in the βp decay of 22 Al, which is not the case. This is another inconsistency between the presently observed branching ratios and the 22 Al βp decay data.…”

“…Unfortunately, there is some disagreement about the properties of levels at E x ∼ 9 MeV. The ENSDF database [41] gives E x = 8991 (7) keV for a state with a tentative J π = 1 − assignment. The J π = 1 − assignment comes from the 21 Na(p, p) 21 Na resonance scattering experiments of He et al and Zhang et al [26,27] in which a state is observed at E x = 9.050 (30) MeV.…”

“…[6]). Simulated X-ray burst lightcurves have shown a dependence on the compactness of neutron stars [7]. Constraints on the compactness from the lightcurve can subsequently be used to limit the range of symmetry-energy parameters of nuclear matter.…”

“…Recent developments have constrained some of these reaction rates [7,[10][11][12][13][14][15][16][17]. For example, the 22 Mg(α, p) 25 Al cross section has been measured using a time-projection chamber at NSCL [7].…”

“…Recent developments have constrained some of these reaction rates [7,[10][11][12][13][14][15][16][17]. For example, the 22 Mg(α, p) 25 Al cross section has been measured using a time-projection chamber at NSCL [7]. The results from this experiment suggest that the 22 Mg(α, p) 25 Al reaction rate is around 8 times smaller than the prediction from the statistical model NON-SMOKER [18] and considerably higher than the rate calculated by Matic et al [19], though the Matic rate was based on only four resonances and should correctly be regarded as a lower limit.…”