Doubly-odd Nuclei Research Articles

Renewed Interest in Spectroscopy of the Lightest Doubly-Odd N = Z Nuclei

The existing experimental data for the γ decay of the stable N=Z doubly-odd nuclei and the β decay of the corresponding isospin multiplets is reviewed. The structure of the lightest nuclei with masses A≤14 is used to test and constrain ab initio nuclear theories. Most of the data were obtained in the second half of the last century and, in some cases, lack the needed precision for comparison with theoretical calculations. Recent spectroscopic studies in the lightest doubly-odd N = Z nuclei are discussed, as well as open problems related to the understanding of their structures and ideas for future experiments.

Evolution of nuclear structure through isomerism in Fr216

Three new isomers have been identified in the transitional odd-odd $^{216}\mathrm{Fr}$ nucleus. The properties of the $({11}^{+})$ isomer with ${T}_{1/2}$ = 9.6(14) ns are compared with those of the similar isomeric states in neighboring doubly-odd nuclei. The experimental results are compared with predictions of shell-model calculations and a fair agreement is observed between the experimental and calculated excitation energies of the $({11}^{+})$ isomeric state and the states to which it decays. The deviation between the measured and calculated reduced transition probabilities suggests contribution from effects other than the single-particle degrees of freedom in these states. Evidence of two high-spin $[{J}^{\ensuremath{\pi}}>({18}^{+})]$ isomers above 2.2 MeV excitation energy with ${T}_{1/2}=7.8(14)$ and 89(9) ns is also presented. These isomers at high excitation energies reflect a pronounced change in the structure above the previously established level scheme, where moderate quadrupole collectivity and octupole correlations were evident.

Theoretical Study of Signature-splitting and Signature-inversion in Doubly-odd Nuclei in A∼80 Mass Region

Projected Shell model calculations have been performed using the angular-momentum projected two-quasiparticle states with the employment of a simple quadrupole-quadrupole + monopole–Pairing + quadrupole-pairing Hamiltonian to study the nuclear structure properties of doubly-odd 80Br and 82Rb isotones. The present calculations reproduce reasonably well the available experimental data on the yrast bands and also predict the new high spin states in these nuclei, where current data are still sparse. The phenomena of Signature-splitting and Signature–inversion have also been studied in detail within the context of Projected Shell Model.

New rotational levels in 186Re nucleus

Excited levels of 186Re have been studied using results of the single γ-ray spectra measurements following the thermal neutron capture reaction. Energies and intensities of more than 500 γ-transitions have been obtained with the high-resolution crystal diffraction spectrometer GAMS5 of ILL. Most of the obtained intense γ-transitions have been placed in the 186Re level scheme. A number of new levels, as well as the depopulation for levels observed earlier in the 187Re(p,d)186Re reaction measurements have been proposed. Structure of 186Re levels is interpreted in terms of two-quasiparticle plus rotor coupling model and compared with that of the neighbouring doubly-odd nucleus 188Re.

Band crossings in 168Ta: A particle-number conserving analysis

The structures of two observed high-spin rotational bands in the doubly-odd nucleus 168Ta are investigated using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments are reproduced very well by the calculations, which confirms the configuration assignments for these two bands in previous works. The backbending and upbending mechanisms in these two bands are analyzed in detail by calculating the occupation probabilities of each orbital close to the Fermi surface and the contributions of each orbital to the total angular momentum alignments. The investigation shows that the level crossings in the first backbending is the neutron i13/2 crossing and the in second upbending is the proton h11/2 crossing.

Systematic study of favoredα-decay half-lives of closed shell odd-Aand doubly-odd nuclei related to ground and isomeric states

In this work, we systematically investigate the favored $\ensuremath{\alpha}$-decay half-lives and $\ensuremath{\alpha}$ preformation probabilities of both odd-$A$ and doubly-odd nuclei related to ground and isomeric states around the doubly magic cores at $Z=82, N=82$ and at $Z=82, N=126$, respectively, within a two-potential approach from the view of the valence nucleon (or hole). The results show that the $\ensuremath{\alpha}$ preformation probability is linearly related to ${N}_{\text{p}}{N}_{\text{n}}$ or ${N}_{\text{p}}{N}_{\text{n}}I$, where ${N}_{\text{p}}, {N}_{\text{n}}$, and $I$ are the number of valence protons (or holes), the number of valence neutrons (or holes), and the isospin of the parent nucleus, respectively. Fitting the $\ensuremath{\alpha}$ preformation probabilities data extracted from the differences between experimental data and calculated half-lives without a shell correction, we give two analytic formulas of the $\ensuremath{\alpha}$ preformation probabilities and the values of corresponding parameters. Using those formulas and the parameters, we calculate the $\ensuremath{\alpha}$-decay half-lives for those nuclei. The calculated results can well reproduce the experimental data.

Large-scale shell model study of the newly found isomer inLa136

The doubly-odd nucleus $^{136}\mathrm{La}$ is theoretically studied in terms of a large-scale shell model. The energy spectrum and transition rates are calculated and compared with the most updated experimental data. The isomerism is investigated for the first ${14}^{+}$ state, which was found to be an isomer in the previous study [Phys. Rev. C 91, 054305 (2015)]. It is found that the ${14}^{+}$ state becomes an isomer due to a band crossing of two bands with completely different configurations. The yrast band with the ($\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\pi}{h}_{11/2}$) configuration is investigated, revealing a staggering nature in $M1$ transition rates.

Investigation of the two-quasiparticle bands in the doubly-odd nucleus 166Ta using a particle-number conserving cranked shell model

The high-spin rotational properties of two-quasiparticle bands in the doubly-odd ${}^{166}$Ta are analyzed using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency $\hbar\omega$ are reproduced very well by the particle-number conserving calculations, which provides a reliable support to the configuration assignments in previous works for these bands. The backbendings in these two-quasiparticle bands are analyzed by the calculated occupation probabilities and the contributions of each orbital to the total angular momentum alignments. The moments of inertia and alignments for the Gallagher-Moszkowski partners of these observed two-quasiparticle rotational bands are also predicted.

A test for correction made to spin systematics for coupled band in doubly-odd nuclei

Systematic Spin Assignments were generally made by using the argument that the energy of levels is a function of neutron number. In the present systematics, the excitation energy of the levels incorporated the effect of nuclear deformation and signature splitting. The nuclear deformation changes toward the mid-shell, therefore a smooth variation in the excitation energy of the levels is observed towards the mid-shell, that intended to make systematics as a function of neutron number towards the mid-shell. Another term “signature splitting” that push the energy of levels for odd- and even-spin sequences up and down, caused the different energy variation pattern for odd- and even-spin sequences. The corrections made in the spin systematics were tested for the known spins of various isotopic chain. In addition, the inconsistency in spin assignments made by the spin systematics and other methods of the configuration π h 11/2 ⊗ νh 11/2 band belonging to 112,114,116Cs, 126Pr, and 138Pr, as an example, was resolved by the correctionmade in the present spin systematics.

A Test for Correction Made to Spin Systematics for Coupled Band in Doubly-Odd Nuclei

A Test for Correction Made to Spin Systematics for Coupled Band in Doubly-Odd Nuclei

Gamma bands in doubly odd rhenium and iridium nuclei

Structure of the |K ± 2| bands in doubly-odd nuclei belonging to the transitional deformation region at A∼190 is discussed. Relation of these quasi gamma-bands with the non-axial deformation of the parent two- quasiparticle configurations is studied. Using available experimental information, new tentative |K ± 2| bands are proposed in 188 Re, and 192,194 Ir nuclei. Coexistence of two-quasiparticle states with different deformation modes is considered in the case of 188 Re and 194 Ir.

Systematic of signature inversion in (h 11/2)p⊗(i 13/2)n for odd–odd nuclei in rare-earth nuclei

Systematic features of the signature inversion phenomenon in (h 11/2)p ⊗(i 13/2)n in doubly-odd rare-earth nuclei are presented. These features are generally observed in high-j orbitals, mainly, in (h 9/2),(h 11/2) and (i 13/2). Calculations are carried out within the framework of the two quasiparticle plus rotor model (TQPRM) to explain strong odd–even staggering and signature inversion observed in these high-j orbitals. The shifting of point of inversion to lower/higher spin with the increase in neutron/proton numbers is well explained by the calculations. It is found that 1 /2[541] proton orbital of h 9/2 is necessary in the lower mass region to obtain the point of inversion.

Erratum: Pair-truncated shell-model analysis for doubly-odd nuclei around mass 130 [Phys. Rev. C88, 034315 (2013)

Erratum: Pair-truncated shell-model analysis for doubly-odd nuclei around mass 130 [Phys. Rev. C<b>88</b>, 034315 (2013)

Unusual Features of rotational bands in 184Au deformed doublyodd nucleus

Two-quasiparticle rotational bands of doubly-odd 184 Au have been investigated. The two quasiparticle plus rotor model (TQPRM) calculations are done for the bands where sufficient experimental data is available mainly for the ground state band{3/2(532)π  7/2(514)v}and the excited bands with configuration {1/2(660)π  9/2(624)v} and {1/2(541)π  9/2(624)v}. Peculiar features like second point of signature inversion, signature reversal and band crossing are observed in these bands of 184 Au. The ambiguity regarding the configuration assignment of ground state band is resolved. The calculations for ground state band clearly show that the proton orbital changes from 3/2(532)π to 1/2(541)π with increasing spin. The mechanism of unusual feature like second point of signature inversion is also presented.

Pair-truncated shell-model analysis for doubly-odd nuclei around mass 130

Pair-truncated shell-model analysis for doubly-odd nuclei around mass 130

Nuclear spectroscopy near the proton drip line in the lanthanide region: The122La nucleus

One of the most exciting subjects in contemporary nuclear physics is the study of nuclei at the limits of stability with respect to particle emission. Recently, there has been an intensive experimental activity in measuring proton decay and a large variety of proton emitters were observed in the region of nuclei with 50 < Z < 82. Very recently, the proton radioactivity from 117La and 121Pr has been identified and the decay rate deviates significantly from calculations assuming spherical configurations, thus indicating the onset of large deformations in the drip line nuclei below Z = 69. Predictions by the microscopicmacroscopicmass model and by relativistic mean field calculations support these experimental results and suggest the position of the proton drip line. The lifetimes of the proton-decaying isomers are extremely sensitive to the orbital angular momentum ` of the emitted proton and can vary over several orders of magnitude when changing the angular momentum of the occupied orbital. The position of certain orbitals at the Fermi surface depends strongly on the beta2 deformation. It is therefore very important to determine the quadrupole deformation of the nuclei at and beyond the proton drip line, in order to locate the orbitals close to the Fermi surface and to estimate the lifetime of the isomers, which is essential when looking for new proton emitters. The deformation of the nuclei at the proton drip line in the A 130 mass region can be experimentally tested by comparing the lifetimes of proton emitters with theoretical predictions and by investigating the level structure of particle bound nuclei close to the drip line. For Z = 57 the proton drip line is predicted to correspond to the isotope 118La. The lightest La nucleus for which spectroscopic information has been published is 124La . This thesis bescribes an experiment realised to identify for the first time excited states of the doubly-odd nucleus 122 57 La65. Another aspect that make particularly interesting a study of these nuclei is a well-established phenomenon in two-quasiparticle rotational bands in odd-odd nuclei: the signature inversion. Despite the observation of signature inversion in many different nuclei, and numerous theoretical interpretations, a satisfactory explanation of the phenomenon has yet to be found. We want verify if the experimental level scheme of 122La is in agreement with the systematics of the other nuclei in this mass region. The common feature relating the studies of these neutron deficient nuclei is that they are populated with extremely low cross section and require special techniques to be identified. The standard efficient way to achieve this is the use of arrays of high-purity germanium detectors coupled to specific ancillary devices for their selection. Our experiment has been performed at the Legnaro National Laboratory (LNL) where heavy-ion fusion-evaporation reaction 40Ca(@ 200 MeV)+92Mo was performed to establish the scheme of 122La by using the GASP -ray spectrometer in conjunction with the ancillary charged-particle ISIS detector and the Neutron Ring. This experimental set-up led to numerous achievements in the A 130 mass region. Chapter 1 introduces to the physics of the nuclei close and beyond to the proton drip-line. In Chapter 2 we will briey see the various theoretical models created to describe several types of nuclear excitations and discuss in more detail the cranking model. Chapter 3 describes the experimental techniques of -ray spectroscopy and the setup used for the present measurement. In Chapter 4 the steps followed in the sorting of the raw data to produce particle-gated matrices are described, together with the techniques used to select the different reaction channels and to clean the spectra. Chapter 5 shows the systematic features of the rotational bands of the A 130 proton rich odd-odd nuclei. Chapter 6 will be devoted to the construction of the decay scheme and to the spins assignments, performed through the analysis of gated matrices, transition intensities, DCO, and the comparison with the systematics of the La isotopes. Finally, in Chapter 7, the results are discussed in the light of the deduced experimental quantities like single-particle spin alignment, dynamic moments of inertia, signature splitting, and B(M1)=B(E2) branching ratios to assign the Nilsson orbitals to the found bands.

Simple Description of Doublet Bands with Mass of Approximately 100

A simple collective model is applied to understand the structure of the ΔI = 1 doublet bands with the νh11/2 ⊗ πg9/2 configuration in the doubly-odd nuclei, 98−104 Tc and 100−106 Rh. In the model, a doubly-odd nucleus is realized when there is one neutron in the 0h11/2 orbital and one proton in the 0g9/2 orbital, and the collective core represents the even-even part of the nucleus. The calculation reproduces the energy spectra and the ratios B(M 1; I → I − 1)/B(E2; I → I − 2) for the doublet bands quite well. The analysis of the wave functions reveals new band structure, showing various angular momentum configurations of the neutron and the proton, weakly coupled with the quadrupole collective excitations of the core.

Application of a quadrupole-coupling model to doublet bands in doubly-odd nuclei

A simple model is applied to the yrast and yrare states based on the νh 11/2 ⊗ πh 11/2 configuration in the doubly-odd nuclei around the mass 130. In the model, the basis state is constructed by one neutron and one proton both in the 0h 11/2 orbital, and by the collective core which couples with the two particles through a quadrupole interaction. The model reproduces quite well the overall energy levels and the electromagnetic transitions. The analysis of the yrast and yrare states reveals that the angular-momentum configuration of the neutron and the proton in the yrast states is different from that in the yrare states, when the two particles are weakly coupled with the quadrupole collective excitations of the core. The strong even-odd staggering of the ratios B(M1;I → I - 1)/B(E2;I → I - 2) for the yrast states is described by the chopsticks-like motion of two angular momenta of the neutron and the proton.

Band structure in doubly-odd nuclei with mass around 130

Nuclear structure of the doublet bands in the doubly-odd nuclei with mass A ∼ 130 is studied in terms of a pair-truncated shell model. The model reproduces quite well the energy levels of the doublet bands and the electromagnetic transitions. The doublet bands turn out to be realized by the chopsticks-like motion of two angular momenta of the unpaired neutron and the unpaired proton, weakly coupled with the quadrupole collective excitations of the even-even part of the nucleus.

New band mechanism of doubly-odd nuclei around mass 130

The nuclear structure of the $\ensuremath{\Delta}I=1$ doublet bands in doubly-odd nuclei $^{130}\mathrm{Cs}$, $^{132}\mathrm{Cs}$, $^{132}\mathrm{La}$, and $^{134}\mathrm{La}$ is studied in terms of a pair-truncated shell model, in which the collective nucleon pairs with angular momenta of zero and two are its basic ingredients. The effective interactions consist of single-particle energies and monopole and quadrupole pairing plus quadrupole-quadrupole interactions, whose strengths are determined so as to describe the level schemes of even-even nuclei in the mass $A~130$ region. The calculation reproduces well the energy levels of the doublet bands and the electromagnetic transitions, especially the staggering of the ratios $B(M1;I\ensuremath{\rightarrow}I\ensuremath{-}1)/B(E2;I\ensuremath{\rightarrow}I\ensuremath{-}2)$ for the yrast states. Through the analysis of the wave functions, the doublet bands turn out to be made of different angular momentum configurations of an unpaired neutron and an unpaired proton, weakly coupled with the quadrupole collective excitations of the even-even part of the nucleus.