High-resolution study ofTz=+1→0Gamow-Teller transitions in theMg26(He

Abstract

In order to study the T z = +1 → 0 Gamow-Teller (GT) transitions in the mass A = 26 system, a chargeexchange reaction 26 Mg( 3 He,t) 26 Al was performed at an incident energy of 140 MeV/nucleon and scattering angle at and near 0• , where T z is the z component of isospin T defined by (N − Z)/2. In this (p,n)-type reaction, it is expected that GT states with T = 0, 1, and 2 are excited. An energy resolution of E = 23 keV allowed us to study many discrete states. Most of the prominent states showed 0• -peaked angular distributions, which suggested that they are the states excited by L = 0 GT transitions. Candidates of GT states were studied up to an excitation energy E x = 18.5 MeV. The reduced GT transition strengths, B(GT), were derived assuming the proportionality between cross sections and B(GT) values. Standard B(GT) values were obtained form the 26 Si β decay, where the mirror symmetry of T z = ±1 → 0 GT transitions was assumed. The GT strength, as a whole, is divided in two energy regions: the region of up to 8.5 MeV and the higher-energy region of 8.5-12.8 MeV, where the strength in the latter region distributed like a resonance. The obtained GT strength distribution is compared with the results of random phase approximation calculations. The T = 2 GT states are expected in the region E x 13.5 MeV. By comparing with the results of (n,p)-type 26 Mg(d, 2 He) 26 Na and 26 Mg(t, 3 He) 26 Na reactions, the isospin symmetry of T = 2 GT states is discussed. Owing to the high-energy resolution, we could study the decay widths for the states in the E x > 9 MeV region. The T = 2 state at 13.592 MeV is not noticeably wider than the experimental energy resolution. The narrow width of the state is explained in terms of isospin selection rules.

s-wave resonances for the 18F(p,$\alpha$α)15O reaction in novae

“…1(a). A peak having normalized ratios within ±20% of unity in all angular ranges was identified as a ΔL = 0 transition (for further examples of this approach, see, e.g., refs [33][34][35][36][37][38]…”

The 26Al Production of the ν e -process in the Explosion of Massive Stars

“…Figure 1 shows that the cross sections for the reaction ( ) e Mg , Al nto all the states and to the single states E X = 0.228, 1.058, and 1.852 MeV of 26 Al vary with neutrino energy. The B(GT) values for the different states are taken from the experimental measurements (Win et al 2017), which are slightly more accurate than those measured by Zegers et al (2006). The energies of the excited states and the corresponding B(GT) are listed in the first and second columns of Table 1, respectively.…”

“…Therefore, we build a simple model to efficiently study the 26 Al produced via the charged-current neutrino-nucleus reaction of core-collapse supernovae (CCSNe) in this work. The average cross sections of the ν e -process are calculated with experimental B(GT) values (Win et al 2017). Then, combining them with a simple model of the CCSNe explosions, neutrino radiation, and temperature evolution, the optimal parameters for the maximum 26 Al yield and the corresponding final ratio of the ejected 26 Al and 26 Mg via the ν e -process are determined to obtain an upper limit of the 26 Al yield.…”