High-resolution study of Gamow-Teller transitions from the $T_z=1$ nucleus ${}^{46}\mathrm{Ti}$ to the $T_z=0$ nucleus ${}^{46}\mathrm{V}$

The Gamow-Teller (GT) transition strengths in fp-shell nuclei are important parameters in presupernova models. A high-energy-resolution (${}^3\mathrm{He}$$,t$) experiment was performed on the $T_z=1$ nucleus ${}^{46}\mathrm{Ti}$ at $0^{°}$ and at an intermediate incident energy of 140 MeV/nucleon for the study of precise GT transition strengths to the final $T_z=0$ nucleus ${}^{46}\mathrm{V}$. With an energy resolution of 33 keV, individual GT transitions were observed and GT strengths were derived for them up to the excitation energy of 4.5 MeV. The GT strengths were compared with shell-model calculations using various effective interactions. In this low-lying region, most GT states have isospin $T=0$. A few GT states with isospin $T=1$ were identified from the existence of the corresponding (analog) $M1$ states in ${}^{46}\mathrm{Ti}$. By comparing the GT strength with the corresponding (analogous) M1 transition strength studied in ${}^{46}\mathrm{Ti}$($e,e^{\text{'}}$) or ($\gamma ,{\gamma }^{\text{'}}$) measurements, a large constructive interference of orbital and spin terms was suggested for one of these $M1$ transitions.

Figure 1

(Color online) The $0^{°}$ ${}^{46}\mathrm{Ti}$(${}^3\mathrm{He}$,$t$)${}^{46}\mathrm{V}$ spectrum. The events with scattering angles $\Theta \le 0.5^{°}$ are included. The energy resolution of 33 keV made it possible to observe discrete states in the excitation energy region up to 6 MeV. Major $L=0$ states of ${}^{46}\mathrm{V}$ are indicated by their excitation energies in megaelectron volts.

Figure 2

Isospin analogous transitions in the $A=46,T_z=\pm 1$ and 0 isobar system are schematically shown. The Coulomb displacement energies are removed so that the isospin symmetry of the system and that of transitions are put in evidence. Analog states with $T=1$ are connected by broken lines. The type of the reaction or decay and the relevant interaction causing each transition are shown along the arrows indicating the transitions.

Figure 3

Comparison of experimental and theoretical B(GT) strength distributions. (a) Measured B(GT) distribution from the ${}^{46}\mathrm{Ti}$(${}^3\mathrm{He}$,t)${}^{46}\mathrm{V}$ reaction. (b) B(GT) distribution from a QD-model calculation. (c) B(GT) distribution from a shell-model calculation using the GXPF1 interaction. (d) B(GT) strengths from a shell-model calculation using the KB3G interaction. Note the change of the ordinate range of the panels.