Multipole Mixing Ratios Research Articles

Multipole mixtures in gamma transitions in 158Gd from the (n, n′γ) reaction

The energy spectrum, the angular distributions, and the linear polarizations of gamma radiation emitted by 158Gd are measured in the (n, n′γ) reaction induced by fast reactor neutrons. The known diagram of levels and gamma transitions is extended. The multipole-mixing ratio δ is found for many gamma transitions between levels with known spin-parity values.

Non-yrast low-spin states in the triaxially deformed nucleus 123Xe

The non-yrast states of 123Xe have been investigated with the reaction 123Te( 3He, 3n) by means of in-beam γ-spectroscopy using a setup of 6 Compton-suppressed high-purity-germanium (HPGe) detectors. More than 130 new transitions establishing over 35 new levels were observed. γγ angular correlations were analyzed to assign spins and parities to the low-lying states, and to determine the multipole mixing ratios of the γ-transitions. With this method 9 spin and parity assignments were made and 19 multipole mixing ratios could be determined. Excitation energies of negative-parity states and the branching ratios of their decays are compared with predictions of the Rigid Triaxial Rotor plus Particle model (RTRP).

Low spin structure of theN=Zodd-odd nucleus2550Mn25

Low spin states in the odd-odd nucleus ${}^{54}\mathrm{Co}$ were investigated with the ${}^{54}\mathrm{Fe}(p,n\ensuremath{\gamma}{)}^{54}\mathrm{Co}$ fusion evaporation reaction at the FN-TANDEM accelerator in Cologne. $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidences, $\ensuremath{\gamma}\ensuremath{\gamma}$-angular correlations, and Compton asymmetries were measured. 28 low spin states were observed. 19 for the first time, eight new spin assignments and six new parity assignments were made, and seven $\ensuremath{\gamma}$-branching ratios were measured for the first time. $M1$ and $E2$ transition strengths between low-lying states in ${}^{54}\mathrm{Co}$ were calculated in the shell-model framework. The experimental branching ratios and multipole mixing ratios indicate the existence of very strong isovector $M1$ transitions.

Structure of positive-parity yrast band in [formula omitted] Br

The states of the positive-parity yrast band in 80 Br have been investigated using the 76 Ge( 7 Li, 3n γ ) reaction at a beam energy of 32 MeV. The band has been extended up to 4450 keV with a spin of (14 + ). Unambiguous spin assignments are made for states up to 2944.0 keV and γ -ray multipole mixing ratios are determined for several ΔJ=1 transitions. Lifetimes studies for the 10 + , 11 + and 12 + states provide an estimate of the quadrupole deformation in this band. Cranking model analysis of the experimental data reveals a signature inversion at a spin of 12 ℏ and a probable neutron alignment at ℏω≈0.7 MeV. The results are discussed within the framework of the systematics of similar bands in the lighter Br isotopes and the cranked-shell model. In addition, a new positive-parity and two negative-parity sequences have been identified.

Electromagnetic properties of low-excitation states in 191Ir and 193Ir and supersymmetry schemes

The electromagnetic properties of low-excitation states in 191Ir and 193Ir have been studied following Coulomb excitation. Gyromagnetic ratios were measured by the transient-field technique and level lifetimes were measured by the Doppler-shift recoil distance method. Multipolarity mixing ratios were determined from measured particle– γ angular correlations. The present lifetime and g-factor results extend the data available for comparison with theory and help discriminate between disparate experimental values reported previously in the literature. We compare the experimental data with particle-triaxial-rotor model calculations and with the predictions of the U(6/4) and U(6/20) supersymmetry models based on the interacting-boson–fermion model.

Magnetic moments in the 1/2−[521] ground-state band of 171Yb and Coriolis-induced renormalization of rotational g-factors in odd-A rare-earth nuclei

Gyromagnetic ratios of the states with spins between 7/2− and 21/2− (inclusive) in the 1/2−[521] ground-state band of 171Yb were measured by the transient-field technique following Coulomb excitation. Multipolarity mixing ratios were determined from measured particle-γ-ray angular correlations and total branching ratios were determined from intensity balances in a γ-γ coincidence measurement. The electromagnetic properties of the low-lying natural parity states in 171Yb are compared with particle-rotor calculations and can be well described in the limit of a pure K=1/2 band. A comparison of measured g-factors in the ground-state rotational bands of 155Gd, 169Tm and 171Yb with particle-rotor model calculations suggests that the renormalization of the rotational g-factor in the low-K, single-quasiparticle bands of odd rare-earth nuclei, compared with their even neighbours, is predominantly due to Coriolis interactions.

Nuclear orientation of the 60 min 148TbGd

Angular distribution of γ rays following the decay of 60 min 148gTb oriented at low temperature in gadolinium was studied. Anisotropies of 35 γ rays were measured, and the E2/M1 and M2/E1 multipole mixing ratios were determined for all mixed transitions. The spin-parities of several levels were established uniquelly or limited.

Low spin structure of theN=Zodd-odd nucleus2346V23

Low spin states in the odd-odd nucleus ${}^{54}\mathrm{Co}$ were investigated with the ${}^{54}\mathrm{Fe}(p,n\ensuremath{\gamma}{)}^{54}\mathrm{Co}$ fusion evaporation reaction at the FN-TANDEM accelerator in Cologne. $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidences, $\ensuremath{\gamma}\ensuremath{\gamma}$-angular correlations, and Compton asymmetries were measured. 28 low spin states were observed. 19 for the first time, eight new spin assignments and six new parity assignments were made, and seven $\ensuremath{\gamma}$-branching ratios were measured for the first time. $M1$ and $E2$ transition strengths between low-lying states in ${}^{54}\mathrm{Co}$ were calculated in the shell-model framework. The experimental branching ratios and multipole mixing ratios indicate the existence of very strong isovector $M1$ transitions.

Magnetic dipole band in124Xe

High-spin states in ${}^{124}\mathrm{Xe}$ were populated in the fusion-evaporation reaction ${}^{110}\mathrm{Pd}{(}^{18}\mathrm{O}{,4n)}^{124}\mathrm{Xe}$ at a beam energy of 86 MeV. The experiment was performed at the NORDBALL spectrometer in Ris\o{}, Denmark. The decay out of a magnetic dipole band was established for the first time in this nucleus. By means of angular correlations from oriented states the multipole mixing ratios for 9 of the 12 gamma transitions of the magnetic dipole band were deduced. The experimental $B(M1;\stackrel{\ensuremath{\rightarrow}}{I}I\ensuremath{-}1)/B(E2;\stackrel{\ensuremath{\rightarrow}}{I}I\ensuremath{-}2)$ values were compared to estimates of the D\"onau-Frauendorf semiclassical model. The dipole band is inferred to be based on a prolate four-quasiparticle configuration of the type $[\ensuremath{\nu}{(h}_{11/2}\ensuremath{\bigotimes}{g}_{7/2})]\ensuremath{\bigotimes}[\ensuremath{\pi}{(h}_{11/2}\ensuremath{\bigotimes}{d}_{5/2}{/g}_{7/2})].$

Measured magnetic moments in 169Tm and the particle-rotor model; implications for transient field calibration

Gyromagnetic ratios were measured in the 1 2 + [411] ground-state band of 169Tm by the transient field technique in such a manner that the extracted g-factors are independent of assumptions concerning the strength and velocity dependence of the transient field. Precise γ-ray branching intensities and multipolarity mixing ratios were determined from measured particle-γ-ray angular correlations. The electromagnetic properties of the low-lying natural parity states in 169Tm are compared with particle-rotor calculations based on the Woods-Saxon potential and the implications of the measured magnetic moments for the calibration of the transient field strength are discussed.

Particulatiries in the properties of 166Er, 160Dy and 148Gd

The results of measurements of the X and γ rays, γ−γ coincidences, conversion electrons and positrons from the decay of 60 min 148g Tb and of the low-temperature nuclear orientation of 166Tm, 160g+mHo and 148g Tb in Gd are reported. Considerably enriched decay scheme of 148g Tb is proposed. Particular interest is paid to the collective bands in 166Er, 160Dy and 148Gd. The sign change of multipole mixing ratios of the ΔI=0 transitions between the veles of the γ-vibration (Kπ=2+) and ground-state (Kπ=0+) bands in 166Er and 160Dy beginning from Ii=4, was observed. The effect seems to be present also in 164Er which suggests the existence of an “island” of nuclei with “anomalous” γ-vibrational bands. The E2/M1 mixing ratios of the ΔI=0 transitions between the β- vibrational (Kπ=0+) and ground-state (Kπ=0+) bands in 160Dy and 148Gd were determined, and the magnitudes of the E0/E2 mixing ratios, |q(E0/E2)|, and the E0/E2 probability ratios, X(E0/E2), were obtained. In general, all these values are consistent with systematics. The |q(E0/E2)|, and X(E0/E2) values for the transition between the negative parity levels, 3−→3−, in 148Gd were firstly determined. The mixing ratio sign change of the γ→g transitions with ΔI=0 is interpreted in the frame of the dynamic deformation model, and this is only the model which describes at present this phenomenon.

Spectroscopy of 155Gd following Coulomb excitation: Signature-independent M1 properties and evidence for octupole correlations

The spectroscopy of 155Gd has been studied following Coulomb excitation. Gyromagnetic ratios were measured in the 3 2 − [521] ground-state band by the transient field technique and the identification of states up to spin 23 2 − in the ground-state band was confirmed by γ-γ coincidence measurements. Level lifetimes were deduced from Doppler broadened lineshapes; γ-ray branching intensities and multipolarity mixing ratios were determined from particle-γ-ray angular correlations. The population of a positive parity band (mainly 3 2 + [651] ) by E3 Coulomb excitation from the ground-state band provides evidence of octupole correlations. Particle-rotor model calculations were performed for the negative parity states. The spectroscopy is best described when the Coriolis interactions are attenuated by ≈50%.

Nuclear orientation of160Hog+mGd: Sign change ofE2/M1mixing ratios inΔK=2transitions of160Dy

Directional distribution of \ensuremath{\gamma} rays following the decay of ${}^{160}{\mathrm{Ho}}^{g+m}$ oriented in a gadolinium host at low temperature has been studied. The \ensuremath{\gamma}-ray anisotropies of transitions from the levels below 3 MeV in ${}^{160}\mathrm{Dy}$ were measured and multipole mixing ratios \ensuremath{\delta} were determined. The variations in both sign and magnitude of \ensuremath{\delta} for the $M1+E2$ transitions between the \ensuremath{\gamma}-vibrational ${(K}^{\ensuremath{\pi}}{=2}^{+})$ and ground-state ${(K}^{\ensuremath{\pi}}{=0}^{+})$ bands were observed. The $E2/M1$ mixing ratios for the $\stackrel{\ensuremath{\rightarrow}}{2}2$ and $\stackrel{\ensuremath{\rightarrow}}{4}4$ transitions from the \ensuremath{\beta}-vibrational ${(K}^{\ensuremath{\pi}}{=0}^{+})$ band to the ground-state band were determined, and the $E0/E2$ probability ratios obtained are consistent with the values for the \ensuremath{\beta}-vibrational bands. The $E2/M1$ mixing ratios of the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}g$ transitions in ${}^{160}\mathrm{Dy}$ obtained previously by the nuclear orientation of ${}^{160}\mathrm{Tb}$ are compared with the present results. The dynamic deformation model is employed to calculate the collective bands, electromagnetic moments, transition probabilities, and mixing ratios in ${}^{160}\mathrm{Dy}.$ A sign change of the $E2/M1$ mixing ratio is predicted for the ${10}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{10}_{g}$ transition. Our experimental results give such a sign change for the ${4}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{4}_{g}$ and ${6}_{\ensuremath{\gamma}}\ensuremath{\rightarrow}{6}_{g}$ transitions. Comparison with the presently determined experimental values of $X(E0/E2)$ for $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}g$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\beta}}g$ transitions is also given.

High-spin levels in 147Tb

The high-spin states of 147Tb have been studied with regard to their spins. The data were obtained by in-beam γ-ray spectroscopy using the reaction 120Sn(31P,4n)147Tb at 152 MeV performed at the Osiris spectrometer in Berlin. We obtained multipole mixing ratios for 60 transitions, and level spins up to 67/2ħ are introduced.

Structural characteristics of144Ndthroughγ-ray spectroscopy following inelastic neutron scattering

Excited levels in ${}^{144}$Nd below 3.3 MeV have been studied using the ${(n,n}^{\ensuremath{'}}\ensuremath{\gamma})$ reaction. Electromagnetic transition probabilities, multipole-mixing and branching ratios, and level spins and parities were deduced from measured $\ensuremath{\gamma}$-ray excitation functions, angular distributions, and Doppler shifts. Mixed-symmetry configurations in low-lying excited states were investigated by comparing experimental electromagnetic transition rates with theoretical calculations made using the interacting boson model and with existing calculations from the quasiparticle phonon model, the cluster vibrator model, and the particle-core coupling model. Fragmentation of the ${2}^{+}$ mixed-symmetry mode is clearly observed through strong $M1$ transitions into the lowest symmetric ${2}^{+}$ level and through small $E2/M1$ multipole-mixing ratios. Comparisons with similar measurements on ${}^{142}\mathrm{Ce}$ reveal that these $N=84$ isotones exhibit strong fragmentation of the mixed-symmetry mode, although it appears to be spread into more levels in ${}^{144}\mathrm{Nd}$. Evidence is found to support the assignment of the 2779.0-keV level as the ${3}^{\ensuremath{-}}$ member of the octupole-quadrupole phonon coupled quintuplet in ${}^{144}\mathrm{Nd}$ and to propose that this excited mode is shared with the 2606.0-keV state. Two- and three-quadrupole phonon excitations, as well as other members of the quadrupole-octupole quintuplet, are also examined.

Nuclear orientation study of the decay of 173Lu

A decay study of 173Lu oriented at low temperatures in a gadolinium host is carried out. Directional distributions of 12 γ-rays in 173Yb are measured using the high-resolution Ge(Li) detectors. The E2 M1 and M2 E1 multipole mixing ratios of mixed γ-transitions are deduced. The energies and structure of the rotational band levels in 173Yb, reduced E2 and M1 transition probabilities and E2 M1 mixing ratios are calculated in the framework of the semi-microscopic quasiparticle-phonon model with a Coriolis interaction included. In general, good agreement is obtained between the experimental results and theory.

\delta(E2/M1) Mixing Ratios For Some Even-Even Tungston Isotopes and Rotational Limit

Low-lying level study of even-even Wolfram is made by the use of IBM-I. It's found that these low-lying levels have rotational natural which corresponds to SU(3) limit of IBM-1. \delta(E2/M1) multipole mixing ratios of transitions in ^{182,184,186}W nuclei are also calculated via IBM-1 with SU(3) symmetry limit. Agreement of calculated values with experimental results are found. It's also possible to extend this method to calculate the other physical concepts belong to these nuclei.

E2/M1 Multipole Mixing Ratios of 162Dy Nucleus in Rotation Vibration Model

The extended rotation-vibration model containing different deformations for protons and neutrons is applied to 162Dy nucleus. The mixing ratios we obtained for the E2/Ml transitions are in reasanably good agreement with previous experimental and theoretical values.

Collective states in 129La

Low-spin states of the odd-proton nucleus 129 La have been investigated by means of in-beam γ-ray spectroscopy. Many new low-lying levels have been established. Of special interest are three new negative-parity bands which are identified as the unfavored yrast- and the favored and unfavored yrare-bands based on a π h 11 2 quasiparticle configuration. The negative-parity states are discussed within the framework of the rigid triaxial rotor plus particle model (RTRP) considering excitation energies, branching and multipole mixing ratios. We are able to establish a value of γ ≈ 16° for the triaxial deformation parameter for 129 La.

Low spin states in 130Ba

Abstract The low spin structure of 130 Ba has been investigated following the β + -decay of ground and medium spin isomeric states of 130 La. The lanthanum nuclei were produced at the Cologne FN-tandem accelerator using the reaction 120 Sn( 14 N,4n) 130 La. γγ-coincidence data was taken by means of the OSIRIS 6-cube spectrometer. Many new low lying levels were established. Of special interest are new “ K = 0”- and “K = 4”- bands . We give the level and transition energies, spins and parities, multipole mixing ratios and B (E2)-ratios obtained from this measurement. The low lying states of positive parity are discussed in the framework of the IBA-1 model and compared with results for the F-spin partner 126 Xe. The description is given in terms of a consistent-Q formalism near the dynamical O(6)-symmetry. A new scheme which gives analytical expressions for the O(6)-wave functions is presented. The scheme is still valid approximately in vicinity of O(6).