Doubly-odd Nuclei Research Articles

Band structures in 116I

The band structures of the doubly-odd nucleus 116I have been studied by using in-beam γ-ray spectroscopy with the 103Rh( 16O, 3n) 116I reaction at an energy of E lab=80 MeV. The beam was provided by the 12UD tandem accelerator at the University of Tsukuba. Absolute excitation energies for the observed collective bands except for a band based on the π(h 11/2) ν(g 7/2) configuration have been definitely determined. The positive-parity rotational band based on the π(h 11/2) ν(h 11/2) configuration is built on the 8 + level at 874.3 keV and exhibits a spin inversion below I=14ℏ. A new vibration-like band built on the 8 − level at 468.5 keV has been identified and can be interpreted as resulting from the π(g 7/2) ν(h 11/2) configuration coupled to the Te core vibration. A negative-parity band built on the 14 − level at 2547.6 keV shows a vibration-like structure and terminates its collectivity at the 24 − level at 6215.0 keV. The total Routhian surface calculations suggest a noncollective oblate state with β 2=0.182 and γ=60° based on a fully aligned six-quasiparticle, π[h 11/2(g 7/2) 2] ν[g 7/2(h 11/2) 2], configuration for this 24 − level. The excitation energy of the 7 − isomer with T 1/2=3.27 μs was found to be at 430.4 keV.

Collective bands in odd–odd 118I

The excited states of the doubly-odd nucleus 118I were investigated by using in-beam gamma-ray spectroscopy with the 103Rh ( 18O, 3n) 118I reaction at an energy of 85 MeV. The beam was provided by the 12UD tandem accelerator at the University of Tsukuba. Several collective bands were identified and their excitation energies were definitely established. The positive-parity collective bands based on the πh 11/2 νh 11/2 configuration and the negative-parity bands based on the πh 11/2 νg 7/2 configuration were newly assigned. An inversion between the favored and unfavored states in the πh 11/2 νh 11/2 band was observed below I=17.5ℏ. The excitation energy of the 7 − isomer with T 1/2=8.5 m was found to be at 188.8 keV.

Statistical Properties of the Realistic Model Spectra for Doubly-Odd Nuclei

The statistical properties of the energy levels calculated for thedoubly-odd nuclei 84Y, 124Cs and 156Tb within thequasiparticle plus axially symmetric rotor model are studied by means ofthe two standard statistical tests of random-matrix theory, i.e. thedistribution function p(s) of the nearest-neighbour levelspacings and the spectral rigidity (Δ3 statistics). We alsoinvestigate the Brody distribution function pB(s) witha single parameter that describes the chaotic degree of the systematicdynamics and the transition behaviour of the spectral fluctuations betweenPoisson and Gauss orthogonal ensemble limits.

Generalization of the N(p)N(n)N(p)N(n) scheme and the structure of the valence space

The N(p)N(n) scheme, which has been extensively applied to even-even nuclei, is found to be a very good benchmark for odd-even, even-odd, and doubly-odd nuclei as well. There are no apparent shifts in the correlations for these four classes of nuclei. The compact correlations highlight the deviant behavior of the Z = 78 nuclei and are used to deduce effective valence proton numbers near Z = 64 as well as to study the evolution of the Z = 64 subshell gap.

Structure of the doubly odd nucleus 180Ta : Description of 23 bands

The structure of the doubly-odd nucleus 180Ta has been studied by γ– γ coincidence measurements with a DC beam at 52 and 57 MeV and time-correlated γ– γ coincidence measurements with a pulsed beam at 55 MeV via the 176Yb( 11B, α3n) 180Ta reaction. In all measurements, γ-rays were detected in coincidence with charged particles. In the time-correlated γ– γ coincidence measurements with a pulsed 11B beam, three rotational bands and one octupole vibrational band have been identified above the I π =15 − T 1/2=30 μs isomer. The configuration of three bands built on 8 + states has been discussed by means of three-band mixing calculations. BCS calculations with blocking have been used in support of configuration assignment of four- and six-quasiparticle structures. Totally, 19 rotational bands, one β-, one γ- and two octupole-vibrational bands, plus one intrinsic state have been identified with two-, four- and six-quasiparticle configurations. The K values of these bands range from 0 to 19. The K-forbidden transition rates are discussed on the basis of mixing between states with widely different K-values. The BBCS calculations predict a K π =22 − isomer not identified experimentally in this nor in previous works. A search for specific intermediate states which could explain the transformation from K π =9 − to 1 + during the astrophysical s- and r- processes was negative.

Numbers of coupled nucleon pairs and the competition between J=0 and T=0 pairs in odd–odd nuclei

The calculation of numbers of coupled nucleon pairs in the shell model is considered. The relation of J=0 and T=0 pair numbers to the competition between low T=| T z | and T=| T z |+1 levels in doubly-odd nuclei is pointed out.

Second proton and neutron alignments in the doubly-odd nuclei154,156Tb

High-spin states in the doubly-odd nuclei {sup 154,156}Tb have been populated in two separate experiments using the {sup 36}S+{sup 124}Sn reaction at different beam energies (160 and 175 MeV). The yrast structures of both nuclei were extended to much higher spin (I{le}48{h_bar}) than previously known and several quasiparticle alignments have been identified. These include the second neutron alignment and a clear delineation of the second proton crossing in {sup 156}Tb. Systematics of these crossings for odd-Z nuclei and comparisons with results of cranked shell model calculations are discussed. thinsp {copyright} {ital 1999} {ital The American Physical Society}

Second proton and neutron alignments in the doubly-odd nuclei 154,156Tb

Second proton and neutron alignments in the doubly-odd nuclei 154,156Tb

Step-wise occupation of theνi13/2intruder orbital in the doubly-odd nucleus132Pr

Five rotational bands involving intruder and/or extruder orbitals have been observed in the doubly-odd nucleus ${}^{132}\mathrm{Pr}.$ One of them is observed for the first time. The properties of the new band are similar to those of the excited highly deformed band of ${}^{134}\mathrm{N}\mathrm{d},$ which has a configuration involving one ${i}_{13/2}$ neutron at low frequency that is crossed at high frequency by a configuration with two ${i}_{13/2}$ neutrons. This behavior indicates that the stepwise occupation of $\ensuremath{\nu}{i}_{13/2}$ intruder orbitals is an efficient mechanism for building high angular momentum in the light $A\ensuremath{\sim}130$ nuclei.

Systematics of signature inversion in doubly-odd nuclei and the role of the [formula omitted] proton orbital

Some general systematic features of the signature inversion phenomenon in doubly-odd lighter rare-earth nuclei are presented. Schematic calculations are carried out within the framework of the two-quasiparticle plus rotor model (TQPRM) to explain these features. It is found that the systematics can be well explained if the h 9 2 : 1 2 [541] proton orbital is included in the calculations in addition to the complete set of h 11 2 proton and i 13 2 neutron orbitals.

In-beam study of the doubly-odd nucleus 61 140 Pm79 above the 8− β +-decaying isomer

An in-beamγ-ray study performed with the114Cd(30Si,p 3n) reaction has established the structure of theN=79 nucleus140Pm. States up toI=(20)ħ and 5.5 MeV excitation energy have been recognized above the 5.95 m isomeric state which we identify, from the GT decay to140Nd, as the 8− member of the (πd 5 2/−1 vh 11 2/−1 ) multiplet, changing the present 7− assignment. The low energy part of the level scheme is discussed in terms of the coupling of the valence holes in respect to theZ=64,N=82 shell closure. A new 8+ isomeric state witht 1/2=1 −0.5 +1 ns has been observed, having most likely a (πh 11/2 vh 11/2 -1 )8 configuration.

A shell-model description of intruder states and shape coexistence

The appearance of low-lying core excitations in nuclei near single closed-shell configurations is discussed in even-even, odd-mass and doubly-odd nuclei. The concept of shell-model intruder states is shown to be a general phenomenon throughout the whole nuclear mass region.

In-beam study of the doubly-odd nucleus 61 140 Pm79

An in-beam γ-ray study performed with the114Cd(30Si,p3n) reaction has established the high-spin states up to 5 MeV excitation energy and I=(21)ħ in the N=79 nucleus140Pm. The low energy part of the level scheme shows both positive and negative parity states which are interpreted as single particle excitations in the 2d5/2 and 1h11/2 orbitals. The level scheme is in qualitative agreement with the coupling of the odd particles to the known yrast levels of the appropriate core nuclei.

Shell-model calculations of the neutron-rich 40Cl nucleus.

The low-lying spectrum of the neutron-rich doubly-odd nucleus $^{40}\mathrm{Cl}$ is studied with a shell-model space consisting of all configurations of neutron and proton 0${d}_{3/2}$ and 0${f}_{7/2}$ orbitals, a space which emphasizes the effects of multiparticle-multihole excitations. The effective interaction among the valence particles was obtained from a systematic fit to the low-lying spectra of nuclei within the model space. The model predictions are compared with other shell-model calculations which emphasize spaces characterized by many orbits but only 0\ensuremath{\Elzxh}\ensuremath{\omega} configurations, as well as with the limited available experimental data.

Structure of nuclei near100Sn and the?g 9/2 ?vg 7/2 Gamow-Teller beta decays

Selected properties of the Gamow-Teller beta decay of even nuclei near100Sn have been studied. Two theoretical models were used: a self-consistent Hartree-Fock-Bogolyubov approach with the Skyrme interaction and a shell-correction model with a Woods-Saxon average field and monopole pairing residual interaction. Calculations reproduce fairly well both theQ EC values and the average energies of theI π=1+ states fed directly in the decay. It is shown that the observed energy splitting between the 1+ states cannot be associated with a stable deformation of a final doubly-odd nucleus. The calculated pairing factors are used to estimate the 0+ → 1+ GT transition strength in the neighbourhood of doubly-magic 50 100 Sn50.

Structure of doubly-odd nucleus 184Ir from the decay of 184Pt

States of 184Ir populated through the β +/EC decay of 184Pt were studied using mass-separated sources and on-line -γ-ray and e − spectroscopic techniques. A rather complete low-spin level scheme is established. Negative and positive parity structures are interpreted within the two-quasiparticle- plus-rotor model. They are mainly the \\ ̃ gp h 9 2 ⊗ \\ ̃ gn i 13 2 structure based on the 5 − ground state and the \\ ̃ gph 9 2 ⊗ \\ ̃ gn 1 2 −[521] system of states based on a 3 + isomer at 225.7 keV.

Weak and strong signature splitting in doubly-odd 132Pr.

An investigation of the collective structures in the doubly-odd nucleus $^{132}\mathrm{Pr}$ has been undertaken with the $^{117}\mathrm{Sn}$${(}^{19}$F,4n${)}^{132}$Pr reaction. Two distinct rotational structures showing both signature components have been established. One band, with no signature splitting, is built on a near-prolate \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${g}_{7/2}$ structure. The second band, with a small signature splitting, involves the \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${h}_{11/2}$ configuration with a triaxial shape. A comparison with recent results for the $^{130}\mathrm{La}$ isotone has been made. A third band structure of large signature splitting (doubly decoupled) was observed showing only one signature component. This band structure is believed to involve the \ensuremath{\beta}-driving \ensuremath{\nu}${i}_{13/2}$${[660](1/2}^{+}$ orbital.

High-spin states in doubly-odd 130La.

Two distinct bands have been populated to high spin in the doubly-odd nucleus $^{130}\mathrm{La}$ following the $^{116}\mathrm{F}$,5n) reaction at 76 MeV. Both bands consist of strong M1 transitions with weaker E2 crossovers. One band, built on the \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${h}_{11/2}$ configuration, has a small signature splitting (\ensuremath{\sim}50 keV) indicating a slightly triaxial shape. The other band, believed to be built on the \ensuremath{\pi}${h}_{11/2}$\ensuremath{\bigotimes}\ensuremath{\nu}${g}_{7/2}$ configuration, shows no signature splitting and is predicted to possess a near-axial prolate shape. Both bands show constant alignment with increasing spin with no low frequency band crossings due to the blocking effect of the ${h}_{11/2}$ proton.

Levels in 154Eu populated by (n, γ) and (d, p) reactions

The structure of the doubly-odd nucleus 154Eu was investigated using neutron capture and (d, p) reactions on 153Eu. The low-energy γ-ray and conversion electron spectra from thermal neutron capture, as well as the γ-ray spectrum for primary energies up to 6.5 MeV, were measured with precision instruments at the Institut Laue-Langevin, Grenoble. The multipolarities were determined for most of the detected low-energy transitions. The (nres, γhigh) spectrum measurements with 2 keV, 2 eV and 3 eV neutrons were performed at Brookhaven National Laboratory for primary transitions leading to the 0–600 keV excitation energies. The 153Eu(d, p)154Eu reaction was measured with the Q3D spectrograph at TU Munich. A level scheme below 600 keV excitation energy comprising 99 levels was deduced and the parities and most probable spin values were determined from the experimental data. The low-lying levels were interpreted as due to the two-particle Nilsson configurations, taking into account the proton orbits 52+[413], 52−[532], 32+[411], and the neutron orbits 112−[505], 32+[651], 32−[521], 32−[532], 52+[642], 32+[402], 52−[523], 12+[400], 12−[530]. The 145.3 (± 0.3) keV level observed in the (d, p) reaction can be identified with the isomeric level with T12 = 46 min. The neutron separation energy for 154Eu was determined to be 6442.0 ± 0.3 keV.

Nature of the 17 keV and associated levels inTm168

Bandhead energy calculations for the low-lying two-quasiparticle states in the doubly-odd nucleus $^{168}\mathrm{Tm}$ have been carried out based on the quantitative evaluation of the zero-range residual neutron-proton interaction. These calculations lead to the configurational assignment ${0}^{+}${(7/2${)}^{+}$[404${]}_{p\ensuremath{-}(7/2{)}^{+}[633{]}_{n}}}$ for the recently established 17 keV excited state in this nucleus. The experimental low-lying unassigned states in $^{168}\mathrm{Tm}$, taken together with the known band structure for this configuration in the neighboring nuclei, suggest five rotational states with ${J}^{\ensuremath{\pi}}$${=1}^{+}$ to ${5}^{+}$ built on the ${K}^{\ensuremath{\pi}}$${=0}^{+}$ bandhead at 17 keV.