NEUTRON DECAY FROM THE ISOBARIC ANALOG STATE IN SB-120 POPULATED IN SN-120(HE-3,T)SB-120 AT E(HE-3)=200 MEV, THETA=0-DEGREES

The Sn-120(He-3,t)Sb-120 charge-exchange reaction has been investigate d at E(He-3) = 200 MeV and theta approximate to 0 degrees to study neu tron decay from the isobaric analog state at E(x)=10.20 MeV in Sb-120. The low-energy neutrons (average energy similar to 0.85 MeV) were det ected in coincidence with tritons observed in the focal plane of a hig h-resolution magnet spectrometer. Four small deuterated NE230 scintill ation detectors were mounted at distances of 9.5 cm from the target re sulting in an overall neutron detection efficiency including solid ang le of >1%. This efficiency was obtained by combining the measured depe ndence on neutron energy with a calculated neutron evaporation spectru m. From the measured ratio of coincidence to singles events a branchin g ratio of >86% was deduced for neutron decay. The observation of isos pin-violating neutron decay with a branching ratio close to 100% is in agreement with the expectation that the escape width (Gamma up arrow) of the isobaric analog state in Sb-120 is small compared to its sprea ding-width (Gamma down arrow). Triton spectra measured in coincidence with gamma rays from the deexcitation of the final nucleus display pro nounced structures related to the thresholds for neutron emission, in agreement with the characteristics of calculated evaporation spectra.