No abstract

No abstract

From the analysis of γ -γ -γ coincidence data taken with Gammasphere of the prompt γ rays in the spontaneous fission of 252 Cf, the 2 + → 0 + transition in 88 Se was identified for the first time. Also, the 4 + → 2 + and 6 + → 4 + transitions in 86 Se were identified along with four new states above 4 + in 84 Se. Surprisingly, the 2 + energy rises in 88 Se compared to 86 Se. This increase in energy could arise from the interaction of a low-lying excited 0 + state with different deformation and the 0 + ground state to depress the ground-state energy.

New level schemes of odd-Z 105,107,109 Tc are proposed based on the 252 Cf spontaneous-fission-gamma data taken with Gammasphere in 2000. Bands of levels are considerably extended and expanded to show rich spectroscopic information. Spin/parity and configuration assignments are made based on determinations of multipolarities of low-lying transitions and the level analogies to the previously reported levels, and to those of the neighboring Rh isotopes. A non-yrast negative-parity band built on the 3 / 2 − ͓301͔ orbital is observed for the first time in 105 Tc. A positive-parity band built on the 1 / 2 + ͓431͔ intruder orbital originating from the ͑g 7/2 / d 5/2 ͒ subshells and having a strong deformation-driving effect is observed for the first time in 105 Tc, and assigned in 107 Tc. A positive-parity band built on the excited 11/ 2 + level, which has rather low excitation energy and predominantly decays into the 9 / 2 + level of the ground state band, provides evidence of triaxiality in 107,109 Tc, and probably also in 105 Tc. Rotational constants are calculated and discussed for the K =1/2 intruder bands using the Bohr-Mottelson formula. Level systematics are discussed in terms of the locations of proton Fermi levels and deformations. The band crossings of yrast positive-parity bands are observed, most likely related to h 11/2 neutron alignment. Triaxial-rotor-plus-particle model calculations performed with = 0.32 and ␥ = −22.5°on the prolate side of maximum triaxiality yielded the best reproduction of the excitation energies, signature splittings, and branching ratios of the positive-parity bands (except for the intruder bands) of these Tc isotopes. The significant discrepancies between the triaxial-rotor-plus-particle model calculations and experiment for the K =1/2 intruder bands in 105,107 Tc need further theoretical studies.Tc with Z = 43, which are odd-Z neighbors of Rh with Z = 45, are carried out. Like the neutron-rich isotopes 111,113 Rh ͑Z =45͒ [6,7], 105,107,109 Tc are several protons below the 50-proton closed shell and midway in the 50-82 neutron shell, a region of nuclei characterized by differing deformations, including ␥ softness or rigid triaxiality. In view of the difference of proton number by two, the Tc isotopes are ex- PHYSICAL REVIEW C 70, 044310 (2004)

No abstract