Gamma-ray spectroscopy in 61Ni-levels above 2.2 MeV in excitation

States in 61Ni were populated using the 58Fe(α, nγ)61Ni and the 53Cr(11B, p2nγ)61Ni reactions. Gamma-gamma coincidence measurements at α particle energies of 8.0, 8.5 and 12.0 MeV and at a 11B energy of 30 MeV were used to determine the decay scheme. Excitation energies, gamma-ray branching ratios, angular distributions, linear polarizations and mixing ratios for levels above 2.2 MeV in excitation were measured at α particle energies of 11.0 and 13.0 MeV. The analysis of the angular distributions and linear polarizations yielded spin and parity assignments of Jsup(π) = 9-/2, (11-/2), 11+/2, 13-/2, 13+/2 and 15+/2 to the levels at 2409, 3259, 3298, 3426, 3435 and 4019 keV respectively. Electromagnetic multipole mixing ratios were determined for several of the gamma-ray transitions. Centroid shifts were extracted from the 11 MeV angular distribution data. The mean lifetimes of the 2409, 3259, 3298 and the 3435 keV levels were deduced using the Doppler-shift attenuation method to be 280 +- 20, 660 +- 60, 870 +300 -150, and 1400 +- 500 fs respectively. The negative parity states are compared with shell-model predictions. (author)