Further experimental evidence for collective effects in 40Ca

Abstract

Measurements of lifetimes, spins and decay modes of levels in 40Ca excited by inelastic proton scattering have been made. The lifetimes were measured using the Doppler shift attenuation technique in a proton-gamma ray coincidence arrangement. The “level” at 6.03 MeV was found to be a doublet, with energies 6.026 MeV and 6.030 MeV. Proton-gamma ray angular correlation measurements, in conjunction with the lifetime results, showed the spins to be 2 − and (3 +, 2 −) respectively. Similar measurements on the levels at 6.51 MeV and 6.54 MeV showed them both to be 4 +. The results of the lifetime measurements are as follows, 5.61 MeV (4 −), 950 −190 +280 fsec: 5.63 MeV (2 +), 76±21 fsec: 5.90 MeV(1 −), 60±20 fsec: 6.026 MeV (2 −), 260±30 fsec: 6.030 MeV (3 +, 2 −), 560±190 fsec: 6.51 MeV(4 +), 160±60 fsec: 6.54 MeV(4 +), 190±60 fsec: 6.58 MeV (3 −), 250±70 fsec. Mixing ratios are also reported: in particular the E2/M1 mixing ratio for the transition between the 2 + states at 5.25 MeV and 3.90 MeV was found to be −13 −6 +3. Levels are identified with the rotational states predicted by Gerace and Green, and the measured E2 matrix elements, some of which are strongly enhanced, are found to be consistent with the model.