Quantitative study of EγEγ correlations in the 122Sn + 106 MeV 12C compound system

Abstract The E γ E γ correlations in the 122 Sn + 106 MeV 12 C compound system have been measured by using the techniques of time of flight to reject events due to neutrons and of unfolding to remove events due to Compton escape. The rotational correlations in the measured matrix can be followed up to E γ = 1.2 MeV which is shown to correspond to a collective spin of 15. An attempt to estimate the amount of aligned angular momentum by utilizing the intensities in the unfolded matrix failed mainly because at least half of all E2 γ-rays showed no rotational correlations. An independent evidence for this background of uncorrelated events is obtained by comparing the rotational correlations in the data with the rotational correlations obtained by simulating the decay of the known discrete levels in 127, 128 Ba on a computer. The comparison indicates that the observed rotational correlations are mainly due to the known discrete transitions. While the moment of inertia obtained from the correlation pattern is less than 80 % of the rigid-body value the high-energy end of the spectrum of E2 radiation can only be explained if γ-ray energy and spin are related by the rigid-body moment of inertia. The area of positive correlations that occurs in most published correlation plots at E 1 = E 2 and at the high-energy end of the E2 radiation is understood from the unfolding to be an artifact of the subtraction procedure.