Excited-State Spin Assignments Based on (n, γγ) Angular-Correlation Measurements on Medium-Weight Nuclei

Abstract

The angular correlations of cascade gamma rays were measured for Ca 45 , Fe 56 , Ni 59 , Ni 61 , and Ni 63 formed by thermal-neutron capture. The observation of large anisotropics allows an unambiguous assignment of J> = §-to be made for states at excitations of 2.24 MeV in Ca 45 , 0.870 MeV in Ni 59 , and 0.158 and 0.526 MeV in Ni 63 -all of which exhibit an 1 = 1 stripping pattern in (d,p) reactions. The data for the 1 = 1 levels at 0.413 MeV in Fe 55 , 0.470 MeV in Ni 59 , and 0.284 MeV in Ni 61 indicate isotropy to within the statistical errors of less than 1.5%, a result that is consistent with an assignment of J r = J~ for these levels. The levels at 1.310 MeV in Ni 59 and 1.008 MeV in Ni 63 have also been assigned J* = %~ on the basis of an observed isotropy, although this assignment is somewhat uncertain because the statistical errors are about 12 and 7%, respectively. The results definitely show that the alleged separation of levels associated with the ^3/2 and pi/2 gross-structure groups is incomplete; J = \ levels exist within the ^3/2 group.