T. Komppa

Structure of odd-A Pm nuclei (I). 147Pm

Abstract The level structure of 147 Pm was studied by methods of in-beam γ-ray and electron spectroscopy using the 148 Nd(p, 2n) reaction. Twenty-four new levels with spins between 1 2 and ( 15 2 ) were observed. The 12 ± 2 ns h 11 2 level at 649.3 keV decays by a strongly hindered El transition (1.2 × 10 −6 s.p.u.) to the 9 2 + level at 408.2 keV and by a M2 transition (0.15 s.p.u.) to the ground state.

Particle octupole multiplet in147Gd

Levels of the N=83 nucleus147Gd have been investigated by in-beam γ-ray and conversion-electron spectroscopy using the147Sm(3He,3n) and Sm(α,n) reactions. We have observed 16 new low-and medium-spin levels in147Gd. In addition to the previously known 13/2+ level we have located the 11/2+,9/2+, 7/2+, 3/2+ and (1/2)+ members of the vf7/2×3 septuplet.

Medium-spin states in the N = 80 nuclei 139Pr and 141Pm

Abstract The level structures of 139 Pr and 141 Pm have been investigated using (p, 2n), ( 3 He, 3n) and (α, 4n) reactions and methods of in-beam γ-ray and electron spectroscopy. Fourteen new levels with spins up to ( 23 2 ) + were observed in 139 Pr and seventeen new levels with spins up to 19 2 − in 141 Pm. The level structures in both nuclei can be described by coupling the odd-proton intrinsic states to the excitations of the doubly even core. The ordering of the levels in the π h 11 2 ⊗2 + multiplet is discussed on the basis of the triaxial rotor-plus-particle model calculations. The calculations suggest that a transition from a basically prolate to an oblate triaxial shape takes place between the neutron numbers N = 78 and N = 80. A γ-deformation of 34° was deduced for both 139 Pr and 141 Pm.

Medium-Spin States in the N=82 Nuclei 141Prand143Pm

The level structures of the N = 82 nuclei 141Pr and 143Pm were studied by methods of in-beam γ-ray and conversion-electron spectroscopy using the (p, 2n) and (p, 3n) reactions. The levels schemes have been built up to energy of about 3 MeV and spin of 19/2. In 141Pr we have established 14 new low- and medium-spin levels.

New 204Au activity and the decay of 202Au

Abstract A new 40 ± 3s activity, assigned to 204 Au, has been found by bombarding natural mercury targets with 14–15 MeV neutrons. The decay of this nucleus and 202 Au ( T 1/2 = 29 ± 3s) has been studied employing Ge(Li), NaI(T1) and plastic detectors and coincidence systems. No trace of the previously reported 4.0 ± 1.0s activity of 204 Au was observed.

Isomeric transition in 198Au

An isomeric 115.2 keV transition from the high-spin 2.36 d state in 198Au has been observed. The multipolarity of this transition is probably M4 and it suggests a configuration of (πh112) (vi132)12− for the isomeric state at 811.9 ± 1.5 keV. The multipolarities E2 (+<2%M1) and M1(+< 20% E2) were determined for the 180.30 and 204.13 keV γ-rays, respectively.

Medium-spin levels and A 360 ns Iπ = 192− isomer in the N = 80 nucleus 137La

Abstract The level structure of 137La has been studied using the 138Ba(p, 2n) reaction and methods of in-beam γ-ray and conversion-electron spectroscopy. The 137La level scheme has been established with 21 new levels with spins up to 19 2 −1 . A 360 ns 19 2 −1 isomer at 1870 keV has been identified and a (π g 7 2 (ν h −1 11 2 d − 3 2 ) 7 − ) 19 2 − configuration is suggested for it. The level ordering of the π h 11 2 ×2 + multiplet has been discussed on the basis of the triaxial rotor-plus-particle model which suggests a slightly oblate triaxial shape to the 137La nucleus.

In-beam study and a rotational description of low-lying levels in the N = 88 nucleus 149 Pm

Abstract Levels of 149 Pm were studied by methods of in-beamy-ray spectroscopy using the 150 Nd(p, 2nγ) reaction. About ten new medium- and high-spin states (from 7 2 to 15 2 ) were observed below 1 MeV. An axial particle-rotor model was applied to the N = 88 nucleus 149 Pm and the calculations were found to predict satisfactorily properties of most levels. Both the positive and the negative-parity band structures are strongly Coriolis-mixed. The results indicate larger deformation for the negative- parity states than for the positive-parity states.

Medium-Spin Levels in 137Ce and the Prolate-Oblate Shape Transition in Ce Nuclei

The level structure of the N = 79 137Ce nucleus has been studied with the 137Ba(3He, 3n) reaction using in beam γ-ray and conversion electron spectroscopy. The level ordering in the vh11/2-1 × 2+ multiplet has been discussed on the basis of the triaxial rotor-plus-particle model which suggests a slightly oblate triaxial shape for 137Ce and the prolate-oblate shape transition in the Ce isotopes to occur between N = 77 and 79.

Reinvestigation of the decay of200Tl

Abstract A detailed study of γ-rays and γ-ray cascades from 26.1 h 200 Tl has been carried out employing Ge(Li) detectors, an anti-Compton spectrometer and a Ge(Li)-NaI(Tl) coincidence spectrometer. A decay scheme is proposed which incorporates six new excited states in 200 Hg. The energies and γ-ray decay branching ratios of some of the levels are compared with values calculated from the model of Covello and Sartoris who describe 200 Hg as two proton holes coupled to surface vibrations.