Neutron decay from the isobaric analog state in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sb}$ populated in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^3$He,t${)}^{120}$Sb at E${(}^3$He) = 200 MeV, θ = 0°

The ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$${(}^3$He,t${)}^{120}$Sb charge-exchange reaction has been investigated at E${(}^3$He) = 200 MeV and θ≊0° to study neutron decay from the isobaric analog state at ${\mathit{E}}_{\mathit{x}}$=10.20 MeV in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sb}$. The low-energy neutrons (average energy ∼0.85 MeV) were detected in coincidence with tritons observed in the focal plane of a high-resolution magnet spectrometer. Four small deuterated NE230 scintillation detectors were mounted at distances of 9.5 cm from the target resulting in an overall neutron detection efficiency including solid angle of ≳1%. This efficiency was obtained by combining the measured dependence on neutron energy with a calculated neutron evaporation spectrum. From the measured ratio of coincidence to singles events a branching ratio of ≳86% was deduced for neutron decay. The observation of isospin-violating neutron decay with a branching ratio close to 100% is in agreement with the expectation that the escape width (${\mathrm{\Gamma }}^{\mathrm{\uparrow }}$) of the isobaric analog state in ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sb}$ is small compared to its spreading width (${\mathrm{\Gamma }}^{\mathrm{\downarrow }}$). Triton spectra measured in coincidence with γ rays from the deexcitation of the final nucleus display pronounced structures related to the thresholds for neutron emission, in agreement with the characteristics of calculated evaporation spectra.