Spectroscopy of 13B via the 13C(t,3He) reaction at 115 AMeV

TL;DR

This study investigates the nuclear structure of 13B using the 13C(t,3He) reaction at 115 AMeV, revealing specific Gamow-Teller and dipole transition strengths and assigning spin-parity to excited states, with results compared to shell-model predictions.

Contribution

It provides new experimental data on 13B transitions and assigns spin-parity to a 3/2- state, enhancing understanding of its nuclear structure and testing shell-model calculations.

Findings

Identification of a 3/2- state at 3.6 MeV in 13B.

Measured Gamow-Teller and dipole transition strengths.

Shell-model calculations generally agree but show some quenching of dipole excitations.

Abstract

Gamow-Teller and dipole transitions to final states in 13B were studied via the 13C(t,3He) reaction at Et = 115 AMeV. Besides the strong Gamow-Teller transition to the 13B ground state, a weaker Gamow-Teller transition to a state at 3.6 MeV was found. This state was assigned a spin-parity of 3/2- by comparison with shell-model calculations using the WBP and WBT interactions which were modified to allow for mixing between nhw and (n+2)hw configurations. This assignment agrees with a recent result from a lifetime measurement of excited states in 13B. The shell-model calculations also explained the relatively large spectroscopic strength measured for a low-lying 1/2+ state at 4.83 MeV in 13B. The cross sections for dipole transitions up to Ex(13B)= 20 MeV excited via the 13C(t,3He) reaction were also compared with the shell-model calculations. The theoretical cross sections exceeded the data by a factor of about 1.8, which might indicate that the dipole excitations are "quenched". Uncertainties in the reaction calculations complicate that interpretation.