H. Helppi

In-beam study of 127, 129Xe and collective description of the level structures in odd-A Xe nuclei

Abstract The levels in 127Xe have been studied with the 126Te(3He, 2n) and 128Te(3He, 4n) reactions and in 129Xe with the 130Te(3He, 4n) and 126Te(α, n) reactions using enriched Te targets and inbeam γ-ray and conversion-electron spectroscopic methods. In addition to the h 11 2 level structures, positive-parity bands based on different low-j; states were observed in both nuclei. The observed g 7 2 band head at 342.2 keV in 127Xe is an isomeric state with a half-life of 37 ± 3 ns. Both triaxial-rotor and core-plus-quasiparticle model calculations have been carried out to explain the observed band structures in 123–129Xe. The calculations indicate different shapes for the positive- and negative-parity level systems.

In-beam study of the 128, 130Xe nuclei

Abstract The level structure of 128,130Xe has been studied in the (α, 2nγ) and (3He, 3nγ) reactions on enriched Te targets using in-beam γ-ray spectroscopic methods. For both nuclei the existing information about positive-parity level structure was enriched and many new negative-parity two-quasiparticle states were observed. Isomeric states with the half-lives of 63 ± 12 ns in 128 Xe and 4.8 ± 0.5 ns in 130 Xe were found. For collective positive-parity states the interacting boson model, and calculations based on Bohr hamiltonian were compared with the experimental data.

In-Beam Study of 122,124,126Xe

Excited states in 122,124,126Xe have been studied with the (3He, 3n) reaction using enriched Te targets and in-beam γ-ray and conversion electron spectroscopy. The existing information on the positive-parity levels is enriched and many new negative-parity states are established. A new 7- isomeric state is observed in 126Xe with a half-life of 1.9(5) ns. Interacting boson model (IBA-1) calculations have been performed to explain the collective level structures.

Level structure in 123Xe

Abstract The level structure of 123 Xe has been studied with the 122 Te( 3 He, 2n) and 123 Te( 3 He, 3n) reactions using in-beam γ-ray spectroscopic methods. Band-like level structures based on the unique-parity h 11 2 neutron state and different low- j states are observed. The isomeric state proposed earlier is established at 185.4 keV with a half-life of 5.6 ± 0.3 μ s, and a new spin assignment of 7 2 − is proposed for this level. A triaxial-rotor-model calculation has been performed to interprete the negative-parity level system. Because of the 7 2 − state, we do not obtain a consistent description of the negative-parity states with the triaxial rotor model, unlike the heavier odd- A Xe nuclei. On the other hand, the positive-parity level structures are interpreted in terms of the core-quasiparticle model supposing a vibrational core. This indicates different core shapes for the positive- and negative-parity level systems.

The E2/M1 mixing of the transitions from the Kπ = 2+ bands in 190, 192Os and 192Pt

Abstract The directional correlation method was used to determine multipole mixing ratios of several γ-transitions in 190, 192 Os and 192 Pt. A new level at 1406.4 keV has been established in 192 Pt. The experimental E2/M1 mixing ratios of the transitions from the γ-bands have been compared with theoretical predictions of the Greiner model also including the rotation-vibration interaction, the Kumar-Baranger model and the Zackrevsky model.

Even- and odd-parity band structures in 125Xe

Abstract The level structure of 125Xe has been studied with the(3He, 3nγ) reaction on an enriched 125Te target using in-beam γ-ray spectroscopic methods. In addition to the negative-parity level structure, an extensive previously unknown positive-parity band structure based on different low-j states was observed. The odd-parity h 11 2 level system is well reproduced with the triaxial rotor model. However, the positive-parity band structure is qualitatively interpreted with a particle-plus-vibrating-core model. The observed g 7 2 band head at 295.9 keV is an isomeric state with a half-life of 140 ± 30 ns.

Study of band crossings in 130Xe

Abstract Excited states in 130Xe were populated in the reaction 130 Te (α, 4 n ) , and the subsequent de-excitation was studied using in-beam γ-ray spectroscopic methods. High-spin states were observed to a possible spin of 19 kh at an excitation energy of 7 MeV. Band-crossings due to h 11 2 neutrons and protons were observed. The triaxial cranked shell model was applied in order to study the quasiparticle content of different bands. Excitation energies of two-quasiparticle states were calculated in the framework of the semiempirical shell model.

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.

Mixing of the transitions from the 3+ quasi γ-band level in 152Gd

Abstract The directional correlation method was used to determine the multipole mixing ratios of some γ-transitions in 152 Gd. The 678.6 and 1089.8 keV γ-rays from the 3 + quasi γ-band level were observed to be almost pure E2 transitions, which is in disagreement with earlier results. The B (E2) ratios of the transitions from this level are consistent with theoretical calculations.