Odd-odd Nuclei Research Articles

Structure of the doublet bands in doubly odd nuclei: The case ofCs128

The structure of the $\Delta J = 1$ doublet bands in $^{128}Cs$ is investigated within the framework of the Interacting Vector Boson Fermion Model (IVBFM). A new, purely collective interpretation of these bands is given on the basis of the used boson-fermion dynamical symmetry of the model. The energy levels of the doublet bands as well as the absolute $B(E2)$ and $B(M1)$ transition probabilities between the states of both yrast and yrare bands are described quite well. The observed odd-even staggering of both $B(M1)$ and $B(E2)$ values is reproduced by the introduction of an appropriate interaction term of quadrupole type, which produces such a staggering effect in the transition strengths. The calculations show that the appearance of doublet bands in certain odd-odd nuclei could be a consequence of the realization of a larger dynamical symmetry based on the non-compact supersymmetry group $OSp(2\Omega /12, R)$.

Time-odd mean fields in covariant density functional theory: Rotating systems

Time-odd mean fields (nuclear magnetism) and their impact on physical observables in rotating nuclei are studied in the framework of covariant density functional theory (CDFT). It is shown that they have profound effect on the dynamic and kinematic moments of inertia. Particle number, configuration and rotational frequency dependences of their impact on the moments of inertia have been analysed in a systematic way. Nuclear magnetism can also considerably modify the band crossing features such as crossing frequencies and the properties of the kinematic and dynamic moments of inertia in the band crossing region. The impact of time-odd mean fields on the moments of inertia in the regions away from band crossing only weakly depends on the relativistic mean field parametrization, reflecting good localization of the properties of time-odd mean fields in CDFT. The moments of inertia of normal-deformed nuclei considerably deviate from the rigid body value. On the contrary, superdeformed and hyperdeformed nuclei have the moments of inertia which are close to rigid body value. The structure of the currents in rotating frame, their microscopic origin and the relations to the moments of inertia have been systematically analysed. The phenomenon of signature separation in odd-odd nuclei, induced by time-odd mean fields, has been analysed in detail.

Neutrino reactions onLa138andTa180via charged and neutral currents by the quasiparticle random-phase approximation

Cosmological origins of the two heaviest odd-odd nuclei, $^{138}$La and $^{180}$Ta, are believed to be closely related to the neutrino-process. We investigate in detail neutrino-induced reactions on the nuclei. Charged current (CC) reactions, $^{138}$Ba$ (\nu_e, e^{-}) ^{138}$La and $^{180}$Hf$ (\nu_e, e^{-}) ^{180}$Ta, are calculated by the standard Quasi-particle Random Phase Approximation (QRPA) with neutron-proton pairing as well as neutron-neutron, proton-proton pairing correlations. For neutral current (NC) reactions, $^{139}$La$ (\nu \nu^{'}) ^{139}${La}$^*$ and $^{181}$Ta$ (\nu, \nu^{'}) ^{181}$Ta$^*$, we generate ground and excited states of odd-even target nuclei, $^{139}$La and $^{181}$Ta, by operating one quasi-particle to even-even nuclei, $^{138}$Ba and $^{180}$Hf, which are assumed as the BCS ground state. Numerical results for CC reactions are shown to be consistent with recent semi-empirical data deduced from the Gamow-Teller strength distributions measured in the ($^{3}$He, t) reaction. Results for NC reactions are estimated to be smaller by a factor about 4 $\sim$ 5 rather than those by CC reactions. Finally, cross sections weighted by the incident neutrino flux in the core collapsing supernova are presented for further applications to the network calculations for relevant nuclear abundances.

Multi-quasiparticle structures up to spin~44ℏin the odd-odd nucleusTa168

High-spin states in the odd-odd nucleus $^{168}\mathrm{Ta}$ have been populated in the $^{120}\mathrm{Sn}$($^{51}\mathrm{V}$,3$n$) reaction. Two multi-quasiparticle structures have been extended significantly from spin $~20\ensuremath{\hbar}$ to above $40\ensuremath{\hbar}$. As a result, the first rotational alignment has been fully delineated and a second band crossing has been observed for the first time in this nucleus. Configurations for these strongly coupled rotational bands are proposed based on signature splitting, $B(M1)/B(E2)$ ratio information, and observed rotation-alignment behavior. Properties of the observed bands in $^{168}\mathrm{Ta}$ are compared to related structures in the neighboring odd-$Z$, odd-$N$, and odd-odd nuclei and are discussed within the framework of the cranked shell model.

SYSTEMATIC CALCULATION OF α-DECAY HALF-LIVES WITHIN GENERALIZED DENSITY-DEPENDENT CLUSTER MODEL

An improved version of the generalized density-dependent cluster model is presented to describe an α particle tunneling through a microscopic potential barrier. The microscopic potential is numerically constructed in the double folding model for both the Coulomb potential and the nuclear potential. The decay width is computed using the integral of the quasibound state wave function, the scattering state wave function, and the difference of potentials. We perform a systematic calculation of α-decay half-lives for even-even, odd-A, and odd-odd nuclei ranging from N = 84 to N = 126. The calculated α-decay half-lives are found to be in good agreement with the experimental values.

Theoretical study of positive-parity doublet bands inCs124

Positive-parity doublet bands in the odd-odd nucleus $^{124}\mathrm{Cs}$ have been studied by using the two quasiparticles plus a triaxial rotor model. The energy spectra and electromagnetic properties are calculated and compared with the available experimental results. Good agreement is obtained in the present calculation. The chiral geometry and its evolution with angular momentum for doublet bands in $^{124}\mathrm{Cs}$ is also exhibited and discussed based on the analysis of the expectation values and the probability distributions of the angular momentum.

A New High-Spin Level Scheme of 128I

High-spin states in the odd-odd nucleus 128I are investigated via the 124Sn(7Li,3n)128I reaction at 28 and 32 MeV beam energies. A new level scheme of 128I is established up to high-spin states at Iπ = 16, including 48 levels and 72 γ transitions. The present level scheme is largely different from the one in a recent publication due to identification of several doublet and triplet γ transitions and their proper placements in the level scheme. The high-spin level structure exhibits no obvious collective properties and is possibly associated with two and multi-quasiparticle configurations.

Alignments, additivity, and signature inversion in odd-oddTa170: A comprehensive high-spin study

High-spin states ($I\ensuremath{\lesssim}50\ensuremath{\hbar}$) of the odd-odd nucleus $^{170}\mathrm{Ta}$ have been investigated with the $^{124}\mathrm{Sn}$(${}^{51}\mathrm{V},5n$) reaction. The resolving power of Gammasphere has allowed for the observation of eleven rotational bands (eight of which are new) and over 430 transitions ($~$$350$ of which are new) in this nucleus. Many interband transitions have been observed such that the relative spins and excitation energies of the $11$ bands have been established. This is an unusual circumstance in an odd-odd study. Configurations have been assigned to most of these bands based upon features such as alignment properties, band crossings, $B(M1)/B(E2)$ ratios, and the additivity of Routhians. A systematic study of the frequency at which normal signature ordering occurs in the $\ensuremath{\pi}{h}_{9/2}\ensuremath{\nu}{i}_{13/2}$ band has been performed and it is found that its trend is opposite to that observed in the $\ensuremath{\pi}{h}_{11/2}\ensuremath{\nu}{i}_{13/2}$ bands. A possible interpretation of these trends is discussed based on a proton-neutron interaction.

Sensitivity of de-excitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory

The relationship between de-excitation energies of superdeformed secondary minima relative to ground states and the density dependence of the symmetry energy is investigated for heavy nuclei using the relativistic mean-field (RMF) model. It is shown that the de-excitation energies of superdeformed secondary minima are sensitive to differences in the symmetry energy that are mimicked by the isoscalar-isovector coupling included in the model. With deliberate investigations on a few Hg isotopes that have data of de-excitation energies, we find that the description for the de-excitation energies can be improved due to the softening of the symmetry energy. Further, we have investigated de-excitation energies of odd-odd heavy nuclei that are nearly independent of pairing correlations, and have discussed the possible extraction of the constraint on the density dependence of the symmetry energy with the measurement of de-excitation energies of these nuclei.

High-spin states of odd-odd nuclei in the [formula omitted] mass region

Efforts have been made in our group to study the band structure of odd-odd nuclei in the A ∼ 170 mass region. We aimed at providing new data of high-spin states and searching for the low-spin signature inversion in the 2-qp bands built on the π h 9 / 2 ⊗ ν i 13 / 2 and π i 13 / 2 ⊗ ν i 13 / 2 configurations. In this talk, main results of our work will be summarized, and some systematic features of signature inversion discussed. The spin and parity assignments for the π i 13 / 2 ⊗ ν i 13 / 2 band in 184Au could be regarded as firm providing a good example for systematic and theoretical investigations.

Structure of degenerate dipole bands in 106In and investigation of similar structure in neighbouring odd-odd isotopes

A pair of degenerate dipole bands with negative parity have been established in 106In. Projected deformed Hartree-Fock calculations were carried out in order to understand the configurations of these bands and similar structures in neighbouring odd-odd nuclei.

Spectroscopy ofHo144using recoil-isomer tagging

Excited states in the proton-unbound odd-odd nucleus $^{144}\mathrm{Ho}$ have been populated using the $^{92}\mathrm{Mo}(^{54}\mathrm{Fe},\mathit{pn})^{144}\mathrm{Ho}$ reaction and studied using the recoil-isomer-tagging technique. The alignment properties and signature splitting of the rotational band above the ${I}^{\ensuremath{\pi}}=({8}^{+})^{144m}\mathrm{Ho}$ isomer have been analyzed and the isomer confirmed to have a $\ensuremath{\pi}{h}_{11/2}\ensuremath{\bigotimes}\ensuremath{\nu}{h}_{11/2}$ two-quasiparticle configuration. The configuration-constrained blocking method has been used to calculate the shapes of the ground and isomeric states, which are both predicted to have triaxial nuclear shapes with $|\ensuremath{\gamma}|\ensuremath{\approx}{24}^{\ifmmode^\circ\else\textdegree\fi{}}$.

Dynamic chirality in the interacting boson model

The chiral interpretation of twin bands in odd-odd nuclei is investigated in the Interacting Boson Model framework. The analysis of the wave functions shows that the possibility for angular momenta of the valence proton, neutron and core to find themselves in the favorable, almost orthogonal geometry is present, but not dominant. Such behavior is found to be similar in nuclei where both the level energies and the electromagnetic decay properties display the chiral pattern, as well as in those where only the level energies of the corresponding levels in the twin bands are close together. The difference in the structure of the two types of chiral candidates nuclei can be attributed to different β and γ fluctuations, induced by the exchange boson-fermion interaction, i.e. by the antisymmetrization of odd fermions with the fermion structure of the bosons. In both cases the chirality is weak and dynamic. Among the nuclei that are candidates for chiral behavior, the best candidate is probably the odd-even 135Nd, where the β and γ fluctuations are strongly reduced and chirality, although dynamic in origin, is rather close to the static limit.

Multi-quasiparticle structures up to spin ~44ħ in the odd-odd nucleus Ta168

Multi-quasiparticle structures up to spin ~44ħ in the odd-odd nucleus Ta168

New effective interaction forf5pg9-shell nuclei

We present a new effective interaction for shell-model calculations in the model space consisting of the single-particle orbits $1{p}_{3/2}$, $0{f}_{5/2}$, $1{p}_{1/2}$, and $0{g}_{9/2}$. Starting with a realistic interaction based on the Bonn-C potential, 133 two-body matrix elements and four single-particle energies are modified empirically so as to fit $400$ experimental energy data out of $69$ nuclei with mass numbers $A=63~96$. The systematics of binding energies, electromagnetic moments and transitions, and low-lying energy levels are described. The soft $Z=28$ closed core is observed, in contrast to the stable $N=50$ shell closure. The new interaction is applied to systematic studies of three different chains of nuclei, Ge isotopes around $N=40$, $N=Z$ nuclei with $A=64~70$, and $N=49$ odd-odd nuclei, focusing especially on the role of the ${g}_{9/2}$ orbit. The irregular behavior of the ${0}_{2}^{+}$ state in Ge isotopes is understood as a result of detailed balance between the $N=40$ single-particle energy gap and the collective effects. The development of the band structure in $N=Z$ nuclei is interpreted in terms of successive excitations of nucleons into the ${g}_{9/2}$ orbit. The triaxial/$\ensuremath{\gamma}$-soft structure in $^{64}\mathrm{Ge}$ and the prolate/oblate shape coexistence in $^{68}\mathrm{Se}$ are predicted, showing a good correspondence with the experimental data. The isomeric states in $^{66}\mathrm{As}$ and $^{70}\mathrm{Br}$ are obtained with the structure of an aligned proton-neutron pair in the ${g}_{9/2}$ orbit. Low-lying energy levels in $N=49$ odd-odd nuclei can be classified as proton-neutron pair multiplets, implying that the obtained single-particle structure in this neutron-rich region appears to be appropriate. These results demonstrate that, in spite of the modest model space, the new interaction turns out to describe rather well properties related to the ${g}_{9/2}$ orbit in various cases, including moderately deformed nuclei.

Shell-model interpretation of high-spin states inI134

New experimental information has been recently obtained on the odd-odd nucleus $^{134}\mathrm{I}$. We interpret the five observed excited states up to the energy of $~3$ MeV on the basis of a realistic shell-model calculation and make spin-parity assignments accordingly. A very good agreement is found between the experimental and calculated energies.

Identification ofγrays fromAu172andαdecays ofAu172,Ir168, andRe164

The very neutron deficient odd-odd nucleus Au172 was studied in reactions of 342 and 348 MeV Kr78 beams with an isotopically enriched Ru96 target. The α decays previously reported for Au172 were confirmed and the decay chain extended down to Tm152 through the discovery of a new α-decaying state in Re164 [Eα=5623(10) keV; t1/2=864−110+150 ms; bα=3(1)%]. Fine structure in these α decays of Au172 and Ir168 were identified. A new α-decaying state was also observed and assigned as the ground state in Au172 [Eα=6762(10) keV; t1/2=22−5+6 ms]. This decay chain was also correlated down to Tm152 through previously reported α decays. Prompt γ rays from excited states in Au172 have been identified using the recoil-decay tagging technique. The partial level scheme constructed for Au172 indicates that it has an irregular structure. Possible configurations of the α-decaying states in Au172 are discussed in terms of the systematics of nuclei in this region and total Routhian surface calculations.5 MoreReceived 30 September 2009DOI:https://doi.org/10.1103/PhysRevC.80.064310©2009 American Physical Society

Chiral bands in odd-odd nuclei with rigid or soft cores

Properties of chiral bands in an odd-odd nucleus, which is treated as a system of an even-even core and a pair of particles in the πh 11/2 ⊗ υh 11/2 -1 configuration, are calculated in the frame of the Core-Particle-Hole Coupling (CPHC) model with either a rigid triaxial or a soft core. The results of calculations for the two different cores are compared. The properties of the nucleus with the rigid, maximally triaxial ( γ = 30°and with the entirely soft core are qualitatively very similar.

α-decay half-lives: Empirical relations

Sets of simple relations for evaluation of the half-lives of \ensuremath{\alpha} transitions between the ground states of parent and daughter nuclei are presented. Experimental data for half-lives in 344 \ensuremath{\alpha} emitters are used for obtaining the sets of equations. The sets of simple expressions are found for the whole data set as well as for heavy and light subsets of nuclei. Terms related to the orbital moment and parity of \ensuremath{\alpha} transition are introduced for the case of \ensuremath{\alpha} decay in even-odd, odd-even, and odd-odd nuclei. The electron screening effect is taken into account.

New description of the doublet bands in doubly odd nuclei

The experimentally observed $\ensuremath{\Delta}I=1$ doublet bands in some odd-odd nuclei are analyzed within the orthosymplectic extension of the interacting vector boson model (IVBM). A new, purely collective interpretation of these bands is given on the basis of the obtained boson-fermion dynamical symmetry of the model. It is illustrated by its application to three odd-odd nuclei from the $A~130$ region, namely $^{126}\mathrm{Pr}$, $^{134}\mathrm{Pr}$, and $^{132}\mathrm{La}$. The theoretical predictions for the energy levels of the doublet bands as well as $E2$ and $M1$ transition probabilities between the states of the yrast band in the last two nuclei are compared with experiment and the results of other theoretical approaches. The obtained results reveal the applicability of the orthosymplectic extension of the IVBM.