Classical-Nova Contribution to the Milky Way’sAl26Abundance: Exit Channel of the KeyAl25(p

Abstract

Classical novae are expected to contribute to the 1809-keV Galactic γ-ray emission by producing its precursor 26Al, but the yield depends on the thermonuclear rate of the unmeasured 25Al(p,γ)26Si reaction. Using the β decay of 26P to populate the key J(π)=3(+) resonance in this reaction, we report the first evidence for the observation of its exit channel via a 1741.6±0.6(stat)±0.3(syst) keV primary γ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured γ-ray energy and intensity with other experimental data on 26Si, we find the center-of-mass energy and strength of the resonance to be E(r)=414.9±0.6(stat)±0.3(syst)±0.6(lit.) keV and ωγ=23±6(stat)(-10)(+11)(lit.) meV, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model 26Al production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic 26Al.

Isospin Mixing RevealsP30(p,γ)S<

“…Despite the relatively low rate of 31 Cl production and limited ability for γ − γ coincidence gating in [27] (and no ability for coincidences in [26]), both experiments have resulted in the identification of new transitions or levels in 31 S; in fact, the isospin T = 3/2 isobaric analog state (IAS) of the 31 Cl ground state was first definitively identified in [26] using 31 Cl beta-delayed gamma decay. However, a comparison to shell-model calculations reveals that there are potentially important J π = (1/2, 3/2, 5/2) + levels that have not yet been observed in the beta decay of 31 Cl. In the present work we report results from a 31 Cl betadelayed gamma decay experiment using a method similar to [31] with significantly improved sensitivity in comparison to [26,27].…”

“…Unfortunately, the rate of this reaction is essentially unconstrained experimentally because the strengths of key 31 S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the beta decay of 31 Cl, we have observed the beta-delayed gamma decay of a 31 S state at Ex = 6390.2(7) keV, with a 30 P(p, γ) 31 S resonance energy of Er = 259.3 (8) keV, in the middle of the 30 P(p, γ) 31 S Gamow window for peak nova temperatures.…”

“…Unfortunately, the rate of this reaction is essentially unconstrained experimentally because the strengths of key 31 S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the beta decay of 31 Cl, we have observed the beta-delayed gamma decay of a 31 S state at Ex = 6390.2(7) keV, with a 30 P(p, γ) 31 S resonance energy of Er = 259.3 (8) keV, in the middle of the 30 P(p, γ) 31 S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state (IAS) at Ex = 6279.0(6) keV, giving it an unambiguous spin and parity of 3/2 + , and making it an important l = 0 resonance for proton capture on 30 P. Inside meteorites retrieved on Earth's surface, grains have been found that exhibit isotopic abundances inconsistent with solar system abundances.…”

“…The beta decay of 31 Cl preferentially populates [26,27] have used both beta-delayed proton and gamma decay through 31 S to yield information about astrophysically relevant states. Despite the relatively low rate of 31 Cl production and limited ability for γ − γ coincidence gating in [27] (and no ability for coincidences in [26]), both experiments have resulted in the identification of new transitions or levels in 31 S; in fact, the isospin T = 3/2 isobaric analog state (IAS) of the 31 Cl ground state was first definitively identified in [26] using 31 Cl beta-delayed gamma decay.…”

Isobaric multiplet mass equation in theA=31,T=3/2quartets

“…The present experiment is one in a series of recent β-delayed γ decay experiments to investigate the sd shell using fast neutron-deficient beams at the National Superconducting Cyclotron Laboratory [16,[38][39][40][41]. In particular, the β-delayed γ decay of 31 Cl was measured using an experimental procedure that was already described in [38].…”