Low Spin Excitations Research Articles

The γ-ray spectroscopy studies of low-spin structures in 210Bi and 206Tl using cold neutron capture reactions

The γ-coincidence studies of low-spin structures of 210Bi and 206Tl are presented. The 210Bi nucleus, populated in thermal neutron capture reaction, was investigated using EXILL HPGe array at Institut Laue-Langevin in Grenoble. The experimental results were compared to the shell-model calculations allowing to draw the conclusions on the nature of the low-spin excitations populated below the neutron binding energy in 210Bi (4.6 MeV). It has been found that some levels cannot be described by the valence proton and neutron couplings, but may arise from couplings of valence particles to the 3- octupole phonon of the doubly magic 208Pb core. Moreover, preliminary results of a low-spin structure measurements of 206Tl by the γ-coincidence technique, making use of the 205Tl(n,γ)206Tl reaction at the FIPPS prompt γ-ray spectroscopy facility of ILL are shown. The population of a large number of excited states of 206Tl above the ground state up to the neutron binding energy (at 6.5 MeV), within a few units of spin is expected. The analysis involving double and triple γ-coincidences and γγ-angular correlations will allow to significantly extend the experimental information on the energy and spin-parity of the levels in 206Tl. This will help shedding light on the proton-hole and neutron-hole couplings near the doubly magic core 208Pb.

Nuclear Data Sheets for A = 89

The evaluated experimental data are presented for 14 known nuclides of mass 89 (Ge, As, Se, Br, Kr, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh). New data on high–spin excitations are available for 89Kr, 89Rb, 89Sr, 89Tc and 89Ru, including a superdeformed structure in 89Tc. Fluorescence studies in 89Y have revealed a large number of new levels in 7–11 MeV range. New two–neutron transfer data are available for 89Zr. New direct and precise measurement of atomic masses of 89Se, 89Br, 89Kr, 89Rb, 89Mo and 89Tc have greatly improved the Q value landscape in this mass region. This work supersedes previous A=89 evaluation published in 1998Si31, and also the older ones 1989Si20, 1975Ko21, and M.W. Johns et al., Nuclear Data Tables A 8, 373 (1970).In spite of extensive experimental work on the isobaric nuclei of this mass chain several deficiencies remain. The identification of 89Rh isotope remains unconfirmed. The half–lives of ground states of 89Ge, 89As and 89Rh have not been measured, only the lower limits are estimated from time–of–flight in a reaction and experimental arrangement, where produced and identified. The decay schemes of 89Ge, 89As, 89Se, 89Ru and 89Rh are not known, and those for 89Tc and 89Mo are incomplete. High–lying (neutron unbound) levels in 89Kr, expected to be populated in the decay of 89Br, have not been investigated. The spins and parities for levels in 89Kr are largely unassigned, while for 89Tc and 89Ru, only few low–spin excitations are established. For 89Rb, little information is available for high–spin structures. Detailed gamma–ray data are available for 88Sr(n,γ)89Sr reaction, but most of these γ rays remain unassigned in a level scheme. Excited state data are nonexistent for 89Ge, 89As, 89Se, 89Br and 89Rh. The 89Y and 89Zr are the most extensively studied nuclei in A=89.

High spin ↔ low spin ultrafast excitation and relaxation of an isolated iron(II) complex.

Picosecond and femtosecond time resolved pump-probe experiments make it possible to study both the low spin (LS) to high spin (HS) and high spin to low spin excitation and relaxation processes in the same isolated iron(II) complex. We demonstrate that both LS → HS and HS → LS can be recorded by changing the pump wavelength and occur on the same time scale.

Band structure of149Ce

The ${}^{149}$Ce nucleus has been studied via prompt $\ensuremath{\gamma}$-ray spectroscopy using the EUROGAM2 Ge array. The 3/2${}^{\ensuremath{-}}$ ground-state band has been extended to medium spins and the 3/2${}^{+}$ band has been connected to low-spin excitations established previously in ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay. No evidence for parity doublets in ${}^{149}$Ce was found.

Low-spin excitations in 146Sm

The low-spin excitations of the nucleus 146Sm which is just two neutrons and two protons away from the N = 82 shell and Z = 64 subshell closures have been investigated by means of the 143Nd (α, n) and 144Nd (α, 2n) fusion-evaporation reactions. We established 47 hitherto unknown energy levels up to 4.7MeV and 75 new transitions. In addition, 7 spin assignments were possible from the γ-γ angular correlation analysis. The structure of the possible candidates for a 2+ ⊗ 3− quadrupole-octupole multiplet are first discussed in terms of the harmonic vibrational model. A comparison of these states with the corresponding ones in the neighboring N = 84 isotones is also presented. Finally, the structure of the 146Sm nucleus is interpreted in terms of the IBA-spdf model. It is shown that the model is able to reproduce the experimental relative transition strengths of the 2+ ⊗ 3− quadrupole-octupole multiplet and also a series of collective properties such as the proposed double-octupole excitations.

Study of low-spin excitations in 100Pd

In the context of the investigation of collectivity in the A = 100 mass region an experiment to measure the low-spin excitations of 100Pd was performed at the Cologne Tandem accelerator with the HORUS cube spectrometer. Besides the determination of excitation and transition energies and branching ratios, data on spins and multipole mixing ratios resulted from the γγ angular correlation analysis. The level scheme was extended and clarified. Nearly 70 γ transitions were identified, thereof 16 for the first time. In addition 11 new energy levels were assigned and 13 multipole mixing ratios were measured for the first time. The newly gained data are compared with theoretical predictions from collective models and the shell model.

Excited levels in 145Pm.

High-spin states in {sup 145}Pm have been studied with TESSA3 operating at NSF Daresbury, through the {sup 134}Xe({sup 15}N,4{ital n}) compound nucleus reaction using a solid xenon target. To determine conversion coefficients and properties of low-spin excitations electron-{gamma} and {gamma}-{gamma} coincidences have been measured following the {sup 146}Nd({ital d},3{ital n}) reaction. An extended level scheme of {sup 145}Pm is proposed and interpreted in terms of single-particle excitations with collective quadrupole and octupole vibrations coupled to them. {copyright} {ital 1996 The American Physical Society.}

Shape coexistence at high spins in the nuclei 68Ge and 72Se

The recent attempt to describe the low-spin excitations in some even Ge and Se nuclei self-consistently by symmetry-projected Hartree-Fock-Bogoliubov-type quasi-particle determinants (EXCITED VAMPIR model) is extended to the high-spin states in the 68Ge and 72Se isotopes. The shape coexistence explaining the properties of the low-spin states persists and manifests itself in the structure of the investigated high-spin bands. The coexistence of oblate and prolate deformed mean fields, dynamical changes of the hexadecapole deformations, and special alignments of the nucleons occupying the g 9 2 spherical shell lead to the prediction of a rather complex feeding pattern for the yrast band, including strong M1, ΔI = 0 transitions, some anomalous small intraband B( E2) transitions, and a particular trend of the g-factor values for different calculated bands. Though a couple of discrepancies remain, the overall agreement with the available experimental results is fairly good.

Low-spin excitations of 202Hg and 204Hg from inelastic neutron scattering spectroscopy

The heaviest stable mercury isotopes, 202Hg and 204Hg, have been studied with the (n, n'γ) reaction. Gamma-ray excitation functions with incident neutron energies up to 3 MeV permitted the placement of many new levels in these nuclei, while γ-ray angular distribution measurements have been used to deduce spin assignments. Several ambiguities and discrepancies about the low-lying level structures were resolved. Comparisons with available theoretical calculations indicate that the level structures of these nuclei are more complex than predicted.