Neutron Alignment Research Articles

Microscopic study of normal deformed bands in 167,169,171Lu

The normal deformed bands of [Formula: see text]Lu isotopes have been studied by using projected shell model approach. The band head spins, configurations and energies of all the normal deformed bands are reproduced well by the above said approach. The present calculations have predicted [Formula: see text] band head spin for [523]7/2− bands of [Formula: see text]Lu. The observed systematics of aligned angular momenta and the experimental differences in frequencies around the backbends for all the normal deformed bands are reproduced well by the theoretical results. Besides this, the observed backbends or upbends in these isotopes may be ascribed to the alignment of a pair of neutrons in the neutron [Formula: see text] orbital. Although the theoretical [Formula: see text] values obtained from the projected shell model wavefunctions overestimate the experimental [Formula: see text] values in [Formula: see text]Lu, yet they are close to the measured values, considering the precision of measurement. The reduction in the theoretical [Formula: see text] values around the band crossing region may be ascribed to change in nuclear structure of yrast bands due to neutron pair alignment in [Formula: see text] orbital.

Parity-doublet bands in the odd- A isotones U237 and Pu239 investigated by a particle-number-conserving method based on the cranked shell model

Based on the reflection-asymmetric Nilsson potential, the parity-doublet rotational bands in odd-$A$ isotones \element{237}U and \element{239}Pu have been investigated by using the particle-number-conserving (PNC) method in the framework of the cranked shell model (CSM). The experimental kinematic moments of inertia (MOIs) and angular momentum alignments are reproduced very well by the PNC-CSM calculations. The significant differences of rotational properties between \element{237}U and \element{239}Pu are explained with the contribution of nucleons occupying proton octupole-correlation pairs of $\pi ^{2} i_{13/2}f_{7/2}$. The upbendings of moments of inertia of the parity-doublet bands in \element{237}U are due to the interference terms of alignments of protons occupying $\pi f_{7/2}$ (${1/2}$) and the high-$j$ intruder $\pi i_{13/2}$ $(1/2, 3/2)$ orbitals. The splittings between the simplex partner bands of the parity-doublet bands in both \element{237}U and \element{239}Pu result from the contribution of alignment of neutron occupying the $\nu d_{5/2}$ ($1/2$) orbital.

Microscopic description of even–even medium-mass tellurium isotopes within the projected shell model

The low-lying energy levels, B(E2) transition probabilities and g-factors of even–even medium-mass tellurium isotopes have been studied by employing the projected shell model (PSM) approach. The oblate ground state deformations are taken in this study that were predicted in previous relativistic Hartree Bogoliubov mean field study. The low-lying yrast and yrare states are reproduced well in these calculations. The energy and configuration of yre states are also predicted. The experimental B(E2) values and their systematics with neutron number are reproduced well in the medium-mass Te isotopes. The experimental data are available for [Formula: see text]-factors of 2[Formula: see text] states of [Formula: see text]Te isotopes which is in line with these calculations. The enhancement of g-factors at spin I = 6[Formula: see text] in all the Te isotopes considered may be attributable to the alignment of protons in [Formula: see text] subshell. Furthermore, the reduction of g-factors at spin [Formula: see text] in [Formula: see text]Te and [Formula: see text] in [Formula: see text]Te may be attributable to the alignment of neutrons in the [Formula: see text] subshell. The 8[Formula: see text] states of [Formula: see text]Te are envisaged to be of [Formula: see text] nature and in [Formula: see text]Te these states are found to be of [Formula: see text] nature.

Nucleon-pair shell model: Effect of non-collective pairs for odd 123−129Sn

In this paper, odd-mass isotopic chain of [Formula: see text]Sn has been studied within the framework of nucleon-pair shell model (NPSM) with the noncollective pair originating from the alignment of two neutrons in the [Formula: see text]h11/2 orbit included. It was found that NPSM can reproduce the properties of the yrast bands satisfactorily, it is crucial to include the noncollective pair in the NPSM. The band structure can be explained as the backbending or the phase transition from vibrational limit to the rotational limit. The mechanism of the yrast band can be explained as band crossing between the ground state band and the S band constructed from the neutron alignment in the [Formula: see text]h11/2 orbit. Our results also suggest that the mechanism of the band structure of those four Sn isotopes can also be interpreted as the competition and transition between collective and noncollective phase.

Investigation of Proton and Neutron Alignment in the Ba and Ce Isotopes within Interaction Interacting Boson Model and Triaxial Rotor Model

In the form of two quasi-particles coupled to a core described by the IBM-1 and Triaxil Rotor models, the high-spin states of the Ba and Ce isotopes are studied. Bands based on both (vh11/2)-2 and (configurations are considered, which is found to be appropriate for this region to better explain band-crossing systems. Between the recent experimental data and the calculated energy spectra and electric transition probability, fair agreement is achieved.

Antimagnetic rotation and role of gradual neutron alignment in $$^{103}\hbox {Pd}$$

Antimagnetic rotation and role of gradual neutron alignment in $$^{103}\hbox {Pd}$$

Investigation of signature inversion in I126 through lifetime measurements

The reduced transition probabilities $B(E2)$ and $B(M1)$ of the negative-parity yrast states of $^{126}\mathrm{I}$ were studied by measuring the lifetimes in picoseconds using the Doppler-shift attenuation method. We investigated the phenomena of signature splitting and inversion using the two quasiparticle-plus triaxial rotor model (PRM). The experimental result---a sharp decrease in the $B(E2)$ values at the signature inversion---indicated a shape change with a possible shift in the axis of rotation. We interpreted this observation as a change in the triaxiality parameter, with values $\ensuremath{\gamma}=\ensuremath{-}{10}^{\ensuremath{\circ}}$ (Lund convention) below the inversion and $\ensuremath{\gamma}={25}^{\ensuremath{\circ}}$ above it and a constant value of axial deformation of $\ensuremath{\beta}\ensuremath{\approx}0.15$. We also assigned the valence particle configuration---neutron in the ${h}_{11/2}$ orbital and proton predominantly in the ${d}_{5/2}$ orbital mixed with the ${g}_{7/2}$ orbital---from the PRM calculation. Furthermore, the calculation reproduced the overall observed behavior of the signature splitting and inversion reasonably well. The observed backbending at the rotational frequency of 0.47 MeV was due to neutron alignment consistent with the second band crossing from the quasiparticle Routhian diagram.

High spin structure of 155Dy

High spin states in 155Dy have been studied by γ-γ coincidence measurements via the 124Sn(36S, 5n)155Dy reaction at a beam energy of 155 MeV. Eight rotational bands have been populated and observed up to high spin (I<91/2).The band features have been analysed within the framework of the cranked shell model. The Ì13/2 neutron alignments and the h11/2 proton alignments are discussed. B(M1)/B(E2) ratios have also been extracted for the strongly coupled bands to deduce further information on the detailed structure of these bands. For the highest states (above spin 30) of the negative parity bands an irregularity in y-ray energies appears which is discussed in terms of band termination.

Possible antimagnetic rotational band and neutron alignment in In113

High-spin states of $^{113}\mathrm{In}$ have been populated using the $^{110}\mathrm{Pd}(^{7}\mathrm{Li},4n)^{113}\mathrm{In}$ reaction at beam energies of 38 and 50 MeV. More than 50 new $\ensuremath{\gamma}$ transitions are observed in $^{113}\mathrm{In}$. Three previously observed magnetic dipole bands are extended to higher spin states, and several new $E2$ crossover transitions within the bands are observed in two of the dipole bands. A new positive-parity $▵I=2$ band built on the $\ensuremath{\pi}{d}_{5/2}$ configuration is established. The known $▵I=2$ band is extended to $51/{2}^{+}$ state, and a gentle up-bend associated to the alignment of neutrons in the normal-parity $\ensuremath{\nu}{g}_{7/2}/{d}_{5/2}$ orbitals is found. The properties of this band are discussed based on the self-consistent tilted axis cranking relativistic mean-field model calculations. The predicted $B(E2)$, deformation parameters ${\ensuremath{\beta}}_{2}$ and $\ensuremath{\gamma}$, and ${J}^{(2)}/B(E2)$ ratios indicate that the $▵I=2$ band based on the $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}$ and $\ensuremath{\pi}{g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}\ensuremath{\bigotimes}\ensuremath{\nu}{({h}_{11/2})}^{2}{({g}_{7/2}/{d}_{5/2})}^{2}$ configurations, has the characteristics of antimagnetic rotation. Furthermore, the two-shears-like mechanism for the possible antimagnetic rotational bands is examined by investigating the orientation of the angular momenta.

High-spin structure in the transitional nucleus Xe131 : Competitive neutron and proton alignment in the vicinity of the N=82 shell closure

The transitional nucleus 131Xe is investigated after multinucleon transfer (MNT) in the 136Xe+208Pb and 136Xe+238U reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA at the Laboratori Nazionali di Legnaro, Italy and as an elusive reaction product in the fusion-evaporation reaction 124Sn(11B,p3n) 131Xe employing the HORUS γ-ray array coupled to a double-sided silicon strip detector (DSSSD) at the University of Cologne, Germany. The level scheme of 131Xe is extended to 5 MeV. A pronounced backbending is observed at ~ω ≈ 0.4 MeV along the negative-parity one-quasiparticle νh11/2(α = −1/2) band. The results are compared to the high-spin systematics of the Z = 54 isotopes and the N = 77 isotones. Large-scale shell-model calculations (LSSM) employing the PQM130, SN100PN, GCN50:82, SN100-KTH and a realistic effective interaction reproduce the experimental findings and provide guidance to elucidate the structure of the high-spin states. Further calculations in 129−132Xe provide insight into the changing nuclear structure along the Xe chain towards the N = 82 shell closure. Proton occupancy in the π 0h11/2 orbital is found to be decisive for the description of the observed backbending phenomenon.

Deformed band structures at high spin in Tl200

High-spin band structures of $^{200}\mathrm{Tl}$ have been studied by $\ensuremath{\gamma}$-ray spectroscopic methods using the $^{198}\mathrm{Pt}(^{7}\mathrm{Li},5n)^{200}\mathrm{Tl}$ reaction at 45 MeV of beam energy. The level scheme of $^{200}\mathrm{Tl}$ has been extended significantly and several new band structures have been established with the observation of 60 new transitions. The $\ensuremath{\pi}{h}_{9/2}\ensuremath{\bigotimes}\ensuremath{\nu}{i}_{13/2}$ oblate band has been extended beyond the particle alignment frequencies. The band structures and the other excited states have been compared with the neighboring odd-odd Tl isotopes. Total Routhian surface calculations have been performed to study the deformation and shape changes as a function of spin in this nucleus. These calculations could reproduce the particle alignment frequency and suggest that the neutron pair alignment in $\ensuremath{\nu}{i}_{13/2}$ orbital induces $\ensuremath{\gamma}$ softness in $^{200}\mathrm{Tl}$.

Characteristics of collectivity along the yrast line in even-even tungsten isotopes

The collective nature of high-spin yrast states in even-even $^{160\ensuremath{-}190}\mathrm{W}$ isotopes was systematically investigated by means of pairing self-consistent Woods-Saxon-Strutinsky calculations using the total Routhian surface approach in $({\ensuremath{\beta}}_{2},\ensuremath{\gamma},{\ensuremath{\beta}}_{4})$ deformation space. The calculated ground-state deformations are consistent with previous calculations and available experimental data. The deformation energy curves are presented to show the shape and softness evolutions, in particular in the triaxial direction. The backbending or upbending behavior in moment of inertia is attributed to band crossing. It is found that the neutron rotation alignment is preferred for most of the W isotopes (e.g., in $^{164\ensuremath{-}180}\mathrm{W}$), while in other nuclei the competition between the neutron and proton alignments may occur, even the proton alignment is favored in the very neutron-deficient nucleus $^{160}\mathrm{W}$. In addition, the evolution and transition between vibrational and rotational collective modes along the yrast line are investigated on the basis of the new centipedelike E-GOS (E-Gamma Over Spin) curves introduced by us, which to some extent explains the existing differences (e.g., in the moment of inertia) between theory and experiment.

Evolution of shape and rotational structure in neutron-deficient118-128Ba nuclei

The evolution of shape and rotational structure along the yrast line in even–even 118−128 Ba isotopes has been systematically investigated by means of pairing self-consistent Woods–Saxon– Strutinsky calculations using the total Routhian surface approach in (β2, γ , β4) deformation space. Based on deformation Routhian curves at different rotational frequencies, the shape instability and softness are evaluated and/or predicted in detail, particularly in the γ direction. The backbending or upbending behavior due to the alignments of neutron or proton h11/2 orbitals in moments of inertia can be basically reproduced, indicating the necessity for the adjustment of the pairing force strength to the experimental data. It is found that the competition between the proton and neutron alignments may depend sensitively on nuclear shape (e.g., in 126 Ba). In addition, the evolution and transition between vibrational and rotational collective modes along the yrast line are investigated on the basis of the centipede-like E-GOS (E-gamma over spin) curves, showing that the existing disagreement between theory and experiment may be to some extent attributed to a lack of the vibration mechanism in the present model.

Towards Superheavies: Spectroscopy of 94 < Z < 98, 150 < N < 154 Nuclei

The heaviest nuclei where excitations above the ground state can be studied lie near Z ~ 100. These nuclear structure studies are important testing grounds for theoretical models that aim to describe superheavy nuclei. To study the highest neutron orbitals (150 ≤ N ≤ 154), we have populated high angular momentum states in a series of Pu (Z = 94), Cm (Z = 96) and Cf (Z = 98) nuclei, via inelastic and transfer reactions, with heavy beams on long-lived radioactive actinide targets. Multiple collective excitation modes and structures were identified, and their configurations deduced. Quasiparticle alignments are mapped, with odd-A band structures helping identify specific orbital contributions via blocking arguments. Higher-order multipole shapes are observed to play a significant role in disentangling competing neutron and proton alignments. The N > 152 data provide new perspectives on physics beyond the N = 152 sub-shell gap.

G-factor measurements of high spin states in 108Cd

The g-factors of the rotational states of the positive parity yrast band from spin I=10 + to spin I=16 + in even-even nucleus 108Cd have been measured by the transient-magnetic-field ion implantation perturbed angular distribution method. The high spin states of 108Cd were populated by the fusion evaporation reaction 76Ge (37Cl, 1p4n) 108Cd. The measured g-factors increase gradually as the spin increases from 10 + to 16 + due to the g7/2 neutron alignment. The g7/2 neutrons are fully aligned at spin I=16+. This state is the band head state of the anti-magnetic rotational band in 108Cd. The measured g-factor of this state is -0.09. The present results support that this band head state may have the configuration \(\pi (g_{9/2})^{-2}_{J=0}\otimes \nu (h_{11/2})^{2}_{J=10}\nu (g_{7/2})^{2}_{J=6}\).

Possible antimagnetic rotational band and neutron alignment in101Pd

High-spin states of ${}^{101}$Pd were studied through in-beam $\ensuremath{\gamma}$-ray spectroscopy by using the reaction ${}^{68}$Zn(${}^{37}$Cl, $1p3n$). The band based on the ${h}_{11/2}$ neutron orbital was extended up to (${\frac{51}{2}}^{\ensuremath{-}}$), and the band based on the ${d}_{5/2}$ neutron orbital was revised. Various transitions decaying to these bands were observed, and consequently several side bands were established. Electric dipole transitions from the $\ensuremath{\nu}{h}_{11/2}$ band to the $\ensuremath{\nu}{d}_{5/2}$ band were also observed. The structure of the $\ensuremath{\nu}{h}_{11/2}$ band is discussed from the viewpoint of antimagnetic rotation based on a semiclassical particle-rotor model by taking neutron alignments into account. The possible existence of octupole correlations is also discussed on the basis of $B(E1)/B(E2)$ ratios for the decays of the $\ensuremath{\nu}{h}_{11/2}$ band.

In-beam spectroscopy of 72Ge

High-spin states in the nucleus 72Ge were investigated via the 70Zn(\( \alpha\), 2n)72Ge reaction at a beam energy of 30MeV, using the AFRODITE spectrometer. One aim of the study was to search for tetrahedral states. There was no evidence for such states in our coincidence data. The existing decay scheme was substantially revised and extended. Several \( \gamma\) -ray placements and level spin-parities were changed, and some 30 new transitions were added to the level scheme. One new negative-parity rotational band was identified. The new band is likely the unfavoured signature partner of the band built on the previously known \(\ensuremath I^{\pi}=3^{-}\) state at 2515keV. The two negative-parity bands are interpreted as involving an aligned octupole vibration which evolves to a four-quasiparticle structure at higher spins. The upbend in the yrast band is interpreted as the AB neutron alignment. The band structures are discussed with reference to Cranked Shell Model calculations, the aligned angular momenta, experimental routhians, and moments of inertia.

Dependence of Quasi-Particle Alignment on Proton Number in N = 44 Isotones 82Sr, 83Y, 84Zr and 85Nb

The g-factors of Ground Rotational Band states of N = 44 isotones 82Sr, 83Y, 84Zr and 85Nb have been measured by the transient-magnetic-field ion implantation perturbed angular distribution (TMF-IMPAD) method. The measured g-factors of 82Sr increase with the increase of spin I, indicating a proton alignment only. Positive peaks appear in the variation of g-factors with spin for 83Y and 84Zr at spin 21/2+ and 10+ respectively, indicating a proton alignment followed by a neutron alignment. A negative peak occurs for 85Nb at the spin 25/2+, indicating a neutron alignment followed by a proton alignment.

Rotational band properties in165Er

High-spin states in ${}^{165}$Er have been studied experimentally using the ${}^{160}$Gd(${}^{9}$Be, 4$n$) reaction at beam energies of 42 and 45 MeV. The previously known bands based on the $5/{2}^{+}[642]$, $5/{2}^{\ensuremath{-}}[523]$, and $11/{2}^{\ensuremath{-}}[505]$ configurations are extended to $(49/{2}^{+})$, $(45/{2}^{\ensuremath{-}})$, and $(31/{2}^{\ensuremath{-}})$ states, respectively. The rotational bands in ${}^{165}$Er generally show gradual alignment processes, indicating strong band interactions associated with the ${i}_{13/2}$ neutron alignments. The band properties are compared with those in the neighboring nuclei and discussed within the framework of the cranked shell model.

Study of dependence of quasi-particle alignment on proton and neutron numbers in A = 80 region through g-factor measurements

Dependence of quasi-particle alignment on proton and neutron numbers has been studied in A = 80 mass region through g-factor measurements by using TMF-IMPAD. The experimental results show that for the nuclides 84Zr, 85Zr and 86Zr with Z = 40 the proton alignment is followed by the neutron alignment in 84Zr and 85Zr, while the neutron alignment is followed by the proton alignment in 86Zr, and for the nuclides 82Sr, 83Y, 84Zr and 85Nb with N = 44 the proton aligns only in 82Sr, the proton alignment occurs first that is followed by the neutron alignment in 83Y and 84Zr and the neutron alignment is followed by the proton alignment in 85Nb. Proton and/or neutron alignments lead to different patterns of the g-factor variation with spin.