Negative parity bands in 100Ru observed in the 100Mo(α, 4n)100Ru reaction

Abstract

In the study of the 100Mo(α, 4n)100Ru reaction at Eα = 45 MeV the ground state band of 100Ru was excited up to Jπ = 10+ and a negative parity band up to Jπ = (15)−. In addition, two negative parity bands were observed, one of which probably has even and the other odd spin states. The experiments encompassed γ-ray angular distribution, coincidence, linear polarization and conversion electron measurements. New levels are reported at Ex = 5130, 5165 (Jπ = (13)−), 5280, 5717 and at 6201 keV (Jπ = (15)−). In addition spin or parity assignments were made for the Ex = 2529, 2953, 2965, 3141, 3356, 3505 and 4233 keV levels as Jπ = 5−, 7−, (6)−, 7−, (8)−, 9− and (11)−, respectively. A 3− state is for the first time observed at Ex = 2180 ± 20 keV in the 100Ru(α, α') reaction at Eα = 104 MeV. Multipolarities, conversion coefficients, branching and quadrupole/dipole amplitude mixing ratios have been determined for many transitions in 100Ru. From a detailed comparison of excitation energies and of the properties of many, even weak, transitions with the results of the interacting boson approximation model, it appears that this simple model provides a good overall parametrization. This supports the description of 100Ru as an anharmonic vibrator with quadrupole and octupole bosons as independent but interacting basic excitation modes. A negative parity band in 101Ru, of which a new level at Ex = 3474 keV is a candidate for the 272− member, is well described by coupling the h112 single particle to the 100Ru quadrupole excitation.