STUDY OF EXCITED-STATES IN KR-85 AND KR-86 - EVIDENCE FOR NEUTRON-CORE EXCITATIONS IN THE N=50 NUCLEUS KR-86

High-spin states of the N=49,50 nuclei Kr-85, Kr-86 have been investig ated via the reactions Se-82(Li-7,p3n) or Se-82(Li-7,p2n), respectivel y, using 32 MeV Li-7 ions. In order to suppress gamma rays arising fro m pure neutron evaporation the measurements of angular distributions a nd relative excitation functions of the gamma rays as well as gammagam ma coincidences have been performed in particle-gamma coincidence mode s. Additional information on excited states in Kr-85 has been obtained in connection with the Se-82(alpha, n) reaction at beam energies betw een 13 and 21 MeV. The level scheme of Kr-85 has been extended by a ne w sequence of high-spin states with excitation energies up to 4.8 MeV and tentative spins up to (23/2) that is built on top of the 17+/2 mus isomer at 1991.8 keV. For Kr-86 a new level scheme of high-spin state s with excitation energies up to 7.9 MeV and tentative spins up to (12 ) has been observed for the first time. The level sequences observed i n Kr-85, Kr-86 are interpreted on the basis of shell-model calculation s in the configuration space 1p3/2, 0f5/2, 1p1/2, and 0g9/2 for the pr otons and 0g9/2 or 0g9/2, 1d5/2 for the neutrons in Kr-85 or Kr-86, re spectively. The inclusion of neutron-core excitations in the calculati ons for Kr-86 results in a remarkably improved agreement between exper imental and calculated level energies. In this way considerable contri butions of neutron-core excitations are strongly suggested for the pos itive-parity yrast states with spins 7HBAR, 9HBAR, and 10HBAR.