Rotor Model Calculations Research Articles

First observation of excited states in 120La and its impact on the shape evolution in the A ≈ 120 mass region

Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.

Evidence for Chiral Wobbler in Nuclei.

Three ΔI=1 bands with the πg_{9/2}⊗νg_{9/2} configuration have been identified in _{35}^{74}Br_{39}. Angular distribution, linear polarization, and lifetime measurements were performed to determine the multipolarity, type, mixing ratio, and absolute transition probability of the transitions. By comparing these experimental observations with the corresponding fingerprints and the quantum particle rotor model calculations, the second and third lowest bands are, respectively, suggested as the chiral partner and one-phonon wobbling excitation built on the yrast band. The evidence indicates the first chiral wobbler in nuclei.

First observation of high-spin states in 116In and possible new region of chirality

High-spin states in neutron-rich indium isotope 116In have been observed for the first time by using incomplete fusion of 7Li on a 116Cd target at a beam energy of 42 MeV. A negative-parity band with πg9/2−1⊗νh11/2 configuration and a pair of positive-parity doublet bands with πg9/2−1⊗ν(g7/2/d5/2)h11/22 configurations have been identified. The positive-parity doublet bands are tentatively interpreted as chiral doublet bands, which is supported by the adiabatic and configuration-fixed constrained triaxial relativistic-mean-field and multiparticle plus rotor model calculations. This observation reports a possible new region of chirality in neutron-rich A≈ 120 mass region.

Lifetime measurements in 80Br and a new region for observation of chiral electromagnetic selection rules

Level lifetimes for the candidate chiral doublet bands of 80Br were extracted by means of the Doppler-shift attenuation method. The absolute transition probabilities derived from the lifetimes agree well with the M1 and E2 chiral electromagnetic selection rules, and are well reproduced by the triaxial particle rotor model calculations. Such good agreements among the experimental data, selection rules of chiral doublet bands and theoretical calculations are rare and outstanding in researches of nuclear chirality. Besides odd-odd Cs isotopes, odd-odd Br isotopes in the A≈ 80 mass region represent another territory that exhibits the ideal selection rules expected for chiral doublet bands.

First observation of the coexistence of multiple chiral doublet bands and pseudospin doublet bands in the A ≈ 80 mass region

Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.

Evidence of octupole correlation in Se79

Two opposite parity bands I and II with eight new parity changing transitions have been identified in $^{79}\mathrm{Se}$ using the fusion-evaporation reaction $^{76}\mathrm{Ge}(^{9}\mathrm{Be}$, $\ensuremath{\alpha}2n$) at ${E}_{\mathrm{Lab}}\ensuremath{\approx}31$ MeV. The $B(M1)$ and $B(E2)$ rates of bands I and II as well as $B(E1)$ values of the linking transitions between the two bands have been determined from lifetime measurements and are compared with reflection asymmetric triaxial particle rotor model calculations. The large $B(E1)$/$B(E2)$ ratios and $B(E1)$ transition rates indicate the existence of a strong octupole correlation in the $^{79}\mathrm{Se}$ nucleus. This is also supported by the calculated potential energy surface, based on the covariant density functional theory within the three-dimensional lattice approach, which is very soft for the octupole shape degree of freedom ${\ensuremath{\beta}}_{30}$. Extracted values of the intrinsic dipole moments $|{D}_{0}|$ from the $B(E1)$ rates for the lower spin states also indicate the octupole correlation in $^{79}\mathrm{Se}$.

Observation of multiphonon transverse wobbling in 133Ba

The low-lying negative parity states in the 133Ba nucleus have been investigated using the 124Sn(13C, 4nγ)133Ba reaction at Elab = 48 MeV. With the addition of new γ-transitions, nω=0,1,2 wobbling bands were identified in this nucleus. The angular correlations and linear polarization measurements have been performed to confirm the spin and parity of the states. Predominant E2 character was obtained for the inter-linking ΔI=1 transitions between the successive phonon (Δnω=1) wobbling bands. The transverse nature of the wobbling bands is concluded on the basis of observed decreasing behavior of the wobbling frequency with increasing spin. The quasiparticle triaxial rotor model calculations are found to be in agreement with the experimentally determined wobbling frequency and the transition probability ratios. This letter reports the first observation of transverse wobbling mode associated with a hole-like quasiparticle.

Study of signature inversion in 123,125I using Particle Rotor Model calculations

The phenomenon of signature inversion in positive parity yrast states of 123,125I nuclei has been studied using the Particle Rotor Model (PRM) calculations. The experimentally observed signature inversion is well reproduced from the PRM calculations. The change in the value of a triaxial parameter [Formula: see text] was observed after the inversion. The PRM calculations were also used to describe the reduced transition probabilities. The derived change in the value of “[Formula: see text]” (in Lund convention) after inversion is interpreted as the change in nuclear shape from near triaxial to tending towards noncollective oblate.

Pseudospin-doublet bands and Gallagher Moszkowski doublet bands in Y100

New transitions in neutron-rich $^{100}\mathrm{Y}$ have been identified in a $^{9}\mathrm{Be}+^{238}\mathrm{U}$ experiment with mass and $Z$ gates to provide full fragment identification. These transitions and high spin levels of $^{100}\mathrm{Y}$ have been investigated by analyzing the high statistics $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence data from the spontaneous fission of $^{252}\mathrm{Cf}$ at the Gammasphere detector array. Two new bands, 14 new levels, and 23 new transitions have been identified. The ${K}^{\ensuremath{\pi}}={4}^{+}$ new band decaying to a $1s$ isomeric state is assigned to be the high-$K$ Gallagher-Moszkowski (GM) partner of the known ${K}^{\ensuremath{\pi}}={1}^{+}$ band, with the $\ensuremath{\pi}5/2[522]\ensuremath{\bigotimes}\ensuremath{\nu}3/2[411]$ configuration. This ${4}^{+}$ band is also proposed to be the pseudospin partner of the new ${K}^{\ensuremath{\pi}}={5}^{+}$ band with a ${5}^{+}\phantom{\rule{4pt}{0ex}}\ensuremath{\pi}5/2[422]\ensuremath{\bigotimes}\ensuremath{\nu}5/2[413]$ configuration, to form a $\ensuremath{\pi}5/2[422]\ensuremath{\bigotimes}\ensuremath{\nu}[312\phantom{\rule{4pt}{0ex}}5/2,3/2]$ neutron pseudospin doublet. Constrained triaxial covariant density-functional theory and quantal particle rotor model calculations have been applied to interpret the band structure and available electromagnetic transition probabilities and are found to be in good agreement with experimental values.

Quadrupole and octupole collectivity in Ba143

Author(s): Morse, C; MacChiavelli, AO; Crawford, HL; Zhu, S; Wu, CY; Wang, YY; Meng, J; Back, BB; Bucher, B; Campbell, CM; Carpenter, MP; Chen, J; Clark, RM; Cromaz, M; Fallon, P; Henderson, J; Janssens, RVF; Jones, MD; Khoo, TL; Kondev, FG; Lauritsen, T; Lee, IY; Li, J; Potterveld, D; Santamaria, C; Savard, G; Seweryniak, D; Stolze, S; Weisshaar, D | Abstract: The neutron-rich barium nuclei have been the subject of intense interest due to the enhanced octupole correlations they are predicted to exhibit. The observation of enhanced octupole collectivity in Ba144,146 as measured in sub-barrier Coulomb excitation, consistent with static octupole deformation, has further heightened this interest. In the present work, these studies are extended to the neighboring odd-mass Ba143 to investigate the interplay between single-particle and collective octupole degrees of freedom. A new measurement of the first 92 - state lifetime is also presented. Reflection-Asymmetric Triaxial Particle Rotor Model calculations indicate that the negative-parity bands in Ba143 can be understood as a decoupled structure of νh9/2 parentage, while the positive-parity bands are built on a decoupled octupole phonon. No evidence for E3 excitation is observed in this work, but an upper limit is placed on the E3 matrix element to the lowest octupole band.

First Observation of Multiple Transverse Wobbling Bands of Different Kinds in ^{183}Au.

We report the first observation of two wobbling bands in ^{183}Au, both of which were interpreted as the transverse wobbling (TW) band but with different behavior of their wobbling energies as a function of spin. It increases (decreases) with spin for the positive (negative) parity configuration. The crucial evidence for the wobbling nature of the bands, dominance of the E2 component in the ΔI=1 transitions between the partner bands, is provided by the simultaneous measurements of directional correlation from the oriented states ratio and the linear polarization of the γ rays. Particle rotor model calculations with triaxial deformation reproduce the experimental data well. A value of spin, I_{m}, has been determined for the observed TW bands below which the wobbling energy increases and above which it decreases with spin. The nucleus ^{183}Au is, so far, the only nucleus in which both the increasing and the decreasing parts are observed and thus gives the experimental evidence of the complete transverse wobbling phenomenon.

Structure of positive parity states in 139Pm

The excited states of 139Pm is investigated via 127I(16O, 4n)139Pm reaction at 84 MeV beam energy. The spin and parity of several states have been determined from the results of angular correlation (RDCO) and linear polarization asymmetry () measurements. The features of four positive parity bands have been determined. A band above state at 1951 keV comprised of strong magnetic dipole transitions has been established and a three-quasi-protons configuration is suggested on the basis of systematic of neighbouring nuclei. Additionally, a new band above state at 228 keV is observed. The states are compared with the modified particle rotor model calculations which indicated πg7/2 configuration for this band.

Multiple chiral bands in $$^{137}$$Nd

Two new bands have been identified in \(^{137}\)Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in \(^{137}\)Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of odd–even and even-even nuclei presenting multiple chiral bands in the Segré chart.

Observation of signature partner bands in Sb117

Rotational band structures and low-lying single-particle levels in $^{117}\mathrm{Sb}$ have been populated using reaction $^{115}\mathrm{In}(\ensuremath{\alpha}$, $2n)^{117}\mathrm{Sb}$ at a beam energy of 28 MeV and investigated using $\ensuremath{\gamma}$-ray spectroscopic techniques. The existing level scheme has been extended with the observation of 31 new transitions. The signature partner of the band structure based on the configuration of $\ensuremath{\pi}{g}_{7/2}\phantom{\rule{4pt}{0ex}}\ensuremath{\bigotimes}\phantom{\rule{4pt}{0ex}}2\mathrm{p}\text{\ensuremath{-}}2\mathrm{h}$ of the $^{116}\mathrm{Sn}$ core has been established in $^{117}\mathrm{Sb}$ for the first time. Several single-particle nonyrast transitions connecting to various band structures have also been identified. Measurements of the DCO ratios, polarization asymmetry and angular distribution of the observed $\ensuremath{\gamma}$ rays have been carried out to assign the spin-parities to the levels of all the band structures and the low-lying single-particle states, populated in the present work. The spin-parities are also determined for the states of the two previously unassigned bands. The lower-spin structures have been interpreted on the basis of large-scale shell-model calculations using OXBASH. Particle Rotor Model (PRM) calculations have been carried out to explain the large signature splitting of the observed signature partner bands.

Transverse wobbling in an even-even nucleus

Two new bands built on the two-quasiparticle $\pi(h_{11/2})^2$ configuration of the even-even nucleus $^{130}$Ba are investigated using constrained triaxial covariant density functional theory combined with quantum particle rotor model calculations. The energy difference between the two bands, as well as the available electromagnetic transition probabilities $B(M1)_{\textrm{out}}/B(E2)_{\textrm{in}}$ and $B(E2)_{\textrm{out}}/B(E2)_{\rm{in}}$, are well reproduced. The analysis of the angular momentum geometry reveals that the higher band represents transverse wobbling motion of a two-quasiparticle configuration. This is the first example of two-quasiparticle wobbling bands in an even-even nucleus.

Chirality of Nd135 reexamined: Evidence for multiple chiral doublet bands

One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus Nd135 which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (MχD) bands in the A≈130 mass region. The properties of the MχD bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed MχD bands in Nd135 represents an important milestone in supporting the existence of MχD in nuclei.Received 6 April 2019Revised 23 May 2019DOI:https://doi.org/10.1103/PhysRevC.100.024314©2019 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCollective levelsCollective modelsElectromagnetic transitionsNuclear spin & parityNuclear structure & decaysNuclear Physics

Experimental Evidence for Transverse Wobbling in ^{105}Pd.

New rotational bands built on the ν(h_{11/2}) configuration have been identified in ^{105}Pd. Two bands built on this configuration show the characteristics of transverse wobbling: the ΔI=1 transitions between them have a predominant E2 component and the wobbling energy decreases with increasing spin. The properties of the observed wobbling bands are in good agreement with theoretical results obtained using constrained triaxial covariant density functional theory and quantum particle rotor model calculations. This provides the first experimental evidence for transverse wobbling bands based on a one-neutron configuration, and also represents the first observation of wobbling motion in the A∼100 mass region.

Triaxiality near the 110Ru ground state from Coulomb excitation

A multi-step Coulomb excitation measurement with the GRETINA and CHICO2 detector arrays was carried out with a 430-MeV beam of the neutron-rich 110Ru (t1/2=12s) isotope produced at the CARIBU facility. This represents the first successful measurement following the post-acceleration of an unstable isotope of a refractory element. The reduced transition probabilities obtained for levels near the ground state provide strong evidence for a triaxial shape; a conclusion confirmed by comparisons with the results of beyond-mean-field and triaxial rotor model calculations.

Signature effects in 2qp bands of doubly even rare-earth nuclei

The two-quasiparticle rotational bands in deformed doubly even nuclei in the rare-earth region have been studied in detail. A number of interesting features like odd-even staggering and signature inversion have been observed. The phenomenon of signature inversion/reversal is observed experimentally in 162 66Dy, 17070Yb and 170 74W in even-even nuclei. Two quasiparticle plus rotor model (TQPRM) calculations are carried out to explain the reverse pattern of signature in 170 74W for the rotational band having configuration \(\{(h_{11/2})_{p} \otimes (d_{5/2})_{p}\}\).

High-spin structures in theXe129nucleus

High-spin states in the Xe-129 nucleus are studied with the reaction Sn-124(Be-9,4n) at a beam energy of 36 MeV. The level scheme is extended significantly. For the positive-parity band, the alpha = +1/2 and the alpha = -1/2 signature components are combined to form a complete band structure based on the 3/2(+) state with spin and parity up to 21/2(+). For the negative-parity band based on the 11/2(-) state, the alpha = +1/2 signature component is newly established and both the alpha = +1/2 and the alpha = -1/2 signature components also form a complete band structure up to the 35/2(-) state. The positive-and negative-parity bands are proposed to originate from nu d(3/2) 3/2(+)[402] and nu h(11/2)11/2(-)[505] Nilsson configurations, respectively. A backbending is observed in the negative-parity band, which originates from the alignments of two h(11/2) protons according to crank shell model calculations. Based on the total Routhian surface and quasiparticle triaxial rotor model calculations, the negative-parity band is interpreted as a triaxially deformed shape with gamma approximate to -30 degrees, while the positive-parity band is associated with. softness, in accordance with previous studies. In the high-spin states, three decoupled bands and one oblate band with gamma approximate to -60 degrees are newly identified. The systematics and other characteristics of these bands are discussed.