High-precision proton angular distribution measurements of C12(p,p′) for the determination of the

Abstract

Background: In stellar environments, carbon is produced exclusively via the 3α process, where three α particles fuse to form 12 C in the excited Hoyle state, which can then decay to the ground state. The rate of carbon production in stars depends on the radiative width of the Hoyle state. While not directly measurable, the radiative width can be deduced by combining three separately measured quantities, one of which is the E 0 decay branching ratio. The E 0 branching ratio can be measured by exciting the Hoyle state in the 12 C(p, p ) reaction and measuring the pair decay of both the Hoyle state and the first 2 + state of 12 C. Purpose: We aim to reduce the uncertainties in the carbon production rate in the universe by measuring a set of proton angular distributions for the population of the Hoyle state (0 + 2 ) and 2 + 1 state in 12 C in 12 C(p, p ) reactions between 10.20 and 10.70 MeV, used in the determination of the E 0 branching ratio of the Hoyle state. Method: Proton angular distributions populating the ground, first 2 + , and the Hoyle states in 12 C were measured in 12 C(p, p ) reactions with a silicon detector array covering 22 • < θ < 158 • in 14 small energy steps between 10.20 and 10.70 MeV with a thin (60 μg/cm 2 ) nat C target. Results: Total cross sections for each state were extracted and the population ratio between the 2 + 1 and Hoyle state determined at each energy step. By appropriately averaging these cross sections and taking xtheir ratio, the equivalent population ratio can be extracted applicable for any thick 12 C target that may be used in pairconversion measurements. This equivalent ratio agreed with a direct measurement performed with a thick target. Conclusions: We present a general data set of high-precision 12 C(p, p ) cross sections that make uncertainties resulting from the population of the 2 + 1 and 0 + 2 states by proton inelastic scattering negligible for any future measurements of the E 0 branching ratio in 12 C. Implications for future measurements are discussed, as well as possible applications of this data set for investigating cluster structures in 13 N.

Resolving the Peak of the Black Hole Mass Spectrum

“…More recently, Freer & Fynbo (2014) have performed an up-to-date review of the relevant literature to affirm the recommended value as Γ rad = 3.7 meV. Recent measurements by Eriksen et al (2020), Kibedi et al (2020), andCook et al (2021) have proposed a revised width of Γ rad = 5.1(6) meV. If true, this would imply an upward revision in the 3α rate at the 37.8% level.…”

Resolving The Peak Of The Black Hole Mass Spectrum

“…More recently Freer & Fynbo (2014) have performed an up to date review of the relevant literature to affirm the recommended value to as Γ rad = 3.7 meV. Recent measurements of by Eriksen et al (2020); Kibédi et al (2020); Cook et al (2021) have measured and proposed a revised width of Γ rad = 5.1(6) meV. If true, this would imply an upward revision in the 3α rate at the 37.8% level.…”

Seismic Signatures of the 12C(α, γ)16O Reaction Rate in White Dwarf Models with Overshooting

“…Helium burning is triggered by the 3α process releasing 7.5 MeV in fusion energy and producing 12 C (Hoyle 1954;Eriksen et al 2020;Kibédi et al 2020;Cook et al 2021). This is a unique process, setting stringent conditions for helium ignition.…”