NUCLEAR-STRUCTURE STUDIES OF LOW-LYING LEVELS OF CA39

The low-lying levels of Ca39 have been studied by means of the Ca40(He3,αγ)Ca39 reaction. Angular-correlation measurements were carried out in a collinear geometry for the ground-state decays of the first three excited states of Ca39. The results of these correlation studies, in conjunction with the results of previous reaction mechanism studies involving the first three Ca39 levels, indicate J=12+,72-,and 32- for the 2.47-, 2.80-, and 3.03-MeV levels, respectively. E3 and E1 multipolarities appear to dominate the 2.80- and 3.03-MeV transitions, respectively. γ-ray decay schemes from the first eight Ca39 levels were also studied. Assuming at least partial dipole character for the γ rays of energy less than 2 MeV, a 72 or 92 assignment was made for the 3.66- and 3.88-MeV levels, and a 1/2 or 32 assignment was made for the 4.02-MeV level. The predominant ground-state transition for the 3.84-MeV level is consistent with a 52- assignment for the level, and with E1 character for the transition. A comparison with the measurements which have been made on the mirror nucleus K39 is made. A hole+Ca40 core-excitation picture for the Ca39-K39 pair is viewed as a simplified model for the low-lying levels, and the parameters for the model were found to be similar to those previously used for the Si27-Al27 pair. © 1968 The American Physical Society.