Pair decay of the 7.65-MeV level of 12C

The ground-state nuclear pair decay branch from the 7.65-MeV 0+ level in 12C has been measured using the reaction 12C(p,p')12C on a 3.5-mg/cm2 thick carbon target at E/sub p/ = 10.5 MeV together with a magnetic pair spectrometer. For normalization the internal pair line due to the 4.44-MeV E2 transition from the first-excited state of 12C was used. In separate measurements the corresponding relative populations of the 7.65- and 4.44-MeV states were determined. The angular distribution of the 4.44-MeV γ rays was also measured in order to obtain the correction to the spectrometer efficiency due to nuclear alignment. A pair decay branch of (7.1 +- 0.8) x 10-6 was obtained for the 7.65-MeV level in agreement with, but somewhat more accurate than previous measurements