Abstract
The Gamow-Teller (GT) transition is a powerful tool to study nuclear structure because of its simple form of the operator στ. The structure of 26Al is studied through Gamow-Teller transitions using nuclear charge-exchange reaction. The reaction 26Mg(3He,t)26Al was performed at an incident energy of 140 MeV/nucleon and scattering angle at and near 0˚. The energy resolution of ΔE = 22 keV allowed us to study many discrete states. Most of the prominent states are suggested that they are excited with ΔL = 0 GT transitions. The GT states were studied up to 18.5 MeV. For the extraction of the B(GT) value, the proportionality between cross section and B(GT) was used. The standard B(GT) values were obtained from the 26Si beta decay, where the mirror symmetry of B(GT) was obtained. The T = 2 GT states are expected in the region Ex ≥ 13.5 MeV. By comparing with the results of 26Mg(t, 3He)26Na reactions, the isospin symmetry of T = 2 GT states is discussed. Due to the high-energy resolution, the decay widths Γ for the states in the Ex > 9 MeV region could be studied. The narrow width of the T = 2 states at 13.592 MeV is explained in terms of isospin selection rules.
Highlights
Gamow-Teller transitions are mediated by the spin-isospin interaction
The excitation energy (Ex) accessible in a β decay is limited by the decay Q value
In order to obtain detailed structural information on 26Al, we investigate GT transitions from the Tz=+1 nucleus 26Mg leading to GT states up to Ex = 18.5 MeV in the Tz =0 nucleus 26Al using a (p, n) type (3He, t) reaction at 140 MeV/nucleon, where Tz is the z component of isospin T defined by (N-Z)/2
Summary
Gamow-Teller transitions are mediated by the spin-isospin (στ) interaction. They are characterized by an angular momentum transfer ΔL = 0 and spin-isospin flip (ΔS = 1 and ΔT = 1). In charge-exchange reactions such as the (p, n), (3He, t), (n, p) and (t, 3He), one can observe GT transitions to states at higher excitation energies without the Q-value limitation. In the charge-exchange reactions, states excited by GT transitions (GT states) become prominent at intermediate incident energies (above 100MeV/nucleon) and forward angles around 0 ̊. This is because of the ΔL = 0 nature of the GT transitions and the dominance of the στ part of the effective nuclear interaction at small momentum transfer q [7, 8]. The B(GT) values for the transitions to higher excited states can be derived using close proportionality given in Eq 2.
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