Gyromagnetic ratios of low-lying rotational states in156, 158, 160Gd

Transient-field precessions were measured simultaneously for levels in the ground-state bands of^{156, 158, 160}Gd as ions of these nuclei traversed a thin polarized Fe foil. Relative g-factors of levels up to 6 ₁ ⁺ were deduced, those of the 4 ₁ ⁺ levels being determined with greatest precision. In contrast with the conclusions of the recent report by Alzner et al. [1], our results are consistent with g(4 ₁ ⁺ ) having the same value in all three isotopes and imply g(2 ₁ ⁺ )=g(4 ₁ ⁺ ) in¹⁵⁶Gd, consistent with nuclear structure models.     

g-factor of the first excited 4+ states in156Gd and158Gd

Relative g-factor of the first 2⁺ and 4⁺ states have been measured with the transient field technique in¹⁵⁶Gd and¹⁵⁸Gd. The precession of gamma rays depopulating the levels under study were observed, after passing through thin polarized gadolinium. The observed values agree with the predictions of the rotational model, i.c. g(4⁺)= g(2⁺), while contrasting the hypothesis that in¹⁵⁶Gd the g-factor of the 4⁺ is reduced with respect to the 2⁺, because of rotational alignment.     

Gyromagnetic ratios of the 4+ and 6+ rotational states of184W

The nuclear Larmor precession has been observed for the 2⁺, 4⁺ and 6⁺ rotational states of¹⁸⁴W in the hyperfine field of WFe by application of the TDPAC and the IPAC techniques. A carrier free radioactive source of^184m Re alloyed with high purity iron was used for all three measurements. From the Larmor precession observed in the 2⁺ state by TDPACω _L = 944(15) MHz and the knowng-factor the hyperfine fieldB _{300 K} ^hf (WFe)=?69.6(27)T was derived. The deviation from the result of a spin echo experiment with¹⁸³WFe extrapolated to room temperature may be caused by the Bohr-Weisskopf effect (hyperfine anomaly). IPAC measurements with the same sample polarized in an external magnetic field of 1.6T gave for the 4⁺ and 6⁺ rotational states: ω _L τ(4⁺)=0.0609(22) andω _L τ(6⁺)=0.00735(102). By use of experimentalB(E2)-values theg _R -factors were derived asg _R (4⁺)=+0.276(26) andg _R (6⁺)=+0.281(45). The directional correlation of the 537?384 keVγ-γ cascade has been analysed in terms of anE1/M2/E3 mixture for theK-forbidden 537keV transition. We obtained the mixing ratiosδ(M2/E1)=±0.086(16),δ(E3/E1)=?0.028(5) with the sign convention of Krane and Steffen.     

Band mixing in156Gd and158Gd

A detailed investigation of the energies and intensities of the γ-rays that depopulate the low spin levels of the β- and γ-vibrational bands of¹⁵⁶Gd and the γ-vibrational band of¹⁵⁸Gd has been conducted. Both singles and γ-γ coincidence measurements were made on sources of 15-d¹⁵⁶Eu and 46-min¹⁵⁸Eu by use of large volume, high resolution Ge(Li) detectors. In addition to the γ-band at 1154.09 keV, twoK ^π=0⁺ bands were observed in¹⁵⁶Gd with band heads at 1049.45 and 1168.11 keV, respectively. The 2⁺ and 3⁺ members of the γ-vibrational band in¹⁵⁸Gd were observed at 1187.12 and 1265.43 keV, respectively, as well as a newK ^π=0⁺ band at 1195.98 keV. A first order perturbational treatment of the branching ratios was applied to both nuclei. In addition, the mixing between the ground state, the β-, and the γ-vibrational bands of¹⁵⁶Gd is considered from two approaches, but neither satisfactorily explains all the experimentalB(E2) ratios.     

Gyromagnetic ratios of excited states in186W

The gyromagnetic ratios of the 4 ₁ ⁺ , 6 ₁ ⁺ , and 2 ₂ ⁺ states in¹⁸⁶W were measured relative to that of the 2 ₁ ⁺ level by means of the transient field implantation perturbedγ-ray angular distribution technique. The nuclei in the states of interest were Coulomb excited using a beam of 220-MeV⁶³Cu projectiles and recoiled swiftly through a thin, polarized Fe foil. The present measurements yielded ratiosg(4 ₁ ⁺ )/g(2 ₁ ⁺ )=1.04±0.07,g(6 ₁ ⁺ )/g(2 ₁ ⁺ )=1.03 ±0.20 andg(2 ₂ ⁺ )/g(2 ₁ ⁺ )=0.63±0.13. The sizable disparity between the measuredg-factors of the ground- and excited-band is examined within the context of the interacting boson approximation model.     

Gyromagnetic ratios of collective states of166Er

The static hyperfine field ofB _hf ^4.2k (ErHo) = 739(18)T of a ferromagnetic holmium single crystal polarized in an external magnetic field of ± 0.48T at ～4.2K was used for integral perturbed γ-γ angular correlation (IPAQ measurements of the g-factors of collective states of¹⁶⁶Er. The 1,200y ^166m Ho activity was used which populates the ground state band and the γ vibrational band up to high spins. The results: $$\begin{gathered} g(4_g^ + ) = + 0.315(16) \hfill \\ g(6_g^ + ) = + 0.258(11) \hfill \\ g(8_g^ + ) = + 0.262(47)and \hfill \\ g(6_\gamma ^ + ) = + 0.254(32) \hfill \\ \end{gathered}$$ exhibit a significant reduction of the g-factors with increasing rotational angular momentum. The followingE2/M1 mixing ratios of interband transitions were derived from the angular correlation coefficients: $$\begin{gathered} 5_\gamma ^ + \Rightarrow 4_g^ + :\delta (810keV) = - (36_{ - 7}^{ + 11} ) \hfill \\ 7_\gamma ^ + \Rightarrow 6_g^ + :\delta (831keV) = - (18_{ - 2}^{ + 3} )and \hfill \\ 7_\gamma ^ + \Rightarrow 8_g^ + :\delta (465keV) = - (63_{ - 12}^{ + 19} ). \hfill \\ \end{gathered}$$ The results are discussed and compared with theoretical predictions.     

Gyromagnetic ratios of excited states in 123, 125Te

The results of integral precession measurements are reported for $\text{3}\text{2}{}^{\mathrm{+}}$ and $\text{5}\text{2}{}^{\mathrm{+}}$ excited states in ^123,125Te. The measurements were made using the ion implantation perturbed angular correlation technique by recoiling the excited nuclei into polarized iron. The measured mean lifetimes and g-factors are: ${}^{123}\text{Te (440 keV,}\text{3}\text{2}{}^{\mathrm{+}}\text{) τ = 39±4 ps, g = 0.34 ± 0.06}$; $\text{(505 keV,}\text{5}\text{2}{}^{\mathrm{+}}\text{) τ = 26±3 ps, g = 0.04±0.025}$; and ${}^{125}\text{Te(443 keV,}\text{3}\text{2}{}^{\mathrm{+}}\text{) ρ = 27±3.3 ps, g = 0.39±0.06}$; $\text{(464 keV,}\text{5}\text{2}{}^{\mathrm{+}}\text{) g = 0.12±0.04}$. The results are compared with theoretical predictions.     

Gyromagnetic ratios of excited states in 150Sm and 152Sm

The gyromagnetic ratios of the 2₁⁺, 4₁⁺, 6₁⁺, 2₂⁺, and 2₃⁺ states in ¹⁵⁰Sm and the 2₁⁺, 4₁⁺, 6₁⁺, 8₁⁺, 10₁⁺, 2₂⁺, and 2₃⁺ levels in ¹⁵²Sm have been measured using the transient field perturbed γ-ray angular correlation technique. States of interest were populated by multiple Coulomb excitation using 150- and 220-MeV ⁵⁸Ni beams. The present results display no significant deviation from constancy of the g-factors of all levels investigated in either isotope separately or of corresponding states in ^150,152Sm. These findings are compared with available prior measurements and assessed in terms of applicable theoretical model calculations.     

Gyromagnetic ratios of first 2+ states in126, 128, 130, 132Xe

Gyromagnetic ratios of first 2⁺ states in^{126, 128, 130, 132}Xe were determined by implantation perturbed angular correlations (IMPAC). The effective hyperfine magnetic field together with the transient magnetic field at xenon nuclei in iron was utilized to obtain the precession of the angular correlation. The precession due to the transient field was taken from systematics to be /g=–36±6 mrad. The effective hyperfine magnetic field was determined in an experiment on¹²⁶Xe in iron to be 900±200 kG. The results for theg-factors areg(128)=0.41±0.07,g(130)=0.38±0.07 andg(132)=0.37±0.05. Theg-factor of the 2⁺ state in¹²⁶Xe was determined in a separate experiment using a radioactive source of¹²⁶I to beg(126)=0.37±0.07, and was used as calibration for the IMPAC-data.     

Mössbauer-effect studies of excited states of 155Gd, 156Gd and 157Gd

Mössbauer-effect studies yield the following nuclear parameters: In ¹⁵⁵Gd, Q(86)/Q(0) = 0.087 ± 0.006, Q(105)/Q(0) = 1.00 ± 0.03. In ${}^{156}\text{Gd}\text{, g(89) = 0.386 ± 0.004,}{}^{156}\text{Q(89)/}{}^{155}\text{Q(0) = ?1.51 ± 0.02.}\text{In}{}^{157}\text{Gd}\text{, Q(64)/Q(0) = 1.80 ± 0.03}\text{and}\text{g(64) = ?0.185 ± 0.005}$. The value of g(89) is in very good agreement with the theoretical value.     

Gyromagnetic ratios of excited states in 107, 109Ag

The gyromagnetic ratios of the lowest excited $\text{3}\text{2}{}^{\mathrm{?}}\text{and}\text{5}\text{2}{}^{\mathrm{?}}$ states in ^{107, 109}Ag were simultaneously measured relative to that of the 2₁⁺ level in ¹⁰⁸Pd. The thin-foil, perturbed γ-ray angular distribution technique was employed utilizing the transient hyperfine magnetic field present at the nuclei of these ions as they swiftly recoiled through a thin magnetized Co foil. The states of interest were Coulomb-excited using beams of 100 MeV ³²S ions. The present measurements yielded $\text{g(}\text{3}\text{2}{}^{\mathrm{?}}\text{;}{}^{107}\text{Ag}\text{) = +0.63 ± 0.09, g(}\text{5}\text{2}{}^{\mathrm{?}}\text{;}{}^{107}\text{Ag}\text{) = + 0.37±0.06, g(}\text{3}\text{2}{}^{\mathrm{?}}\text{;}{}^{109}\text{Ag}\text{) = +0.77 ± 0.10,}\text{and}\text{g(}\text{5}\text{2}{}^{\mathrm{?}}\text{;}{}^{109}\text{Ag}\text{) = +0.36 ± 0.05}$. These findings are compared with weak-coupling and other appropriate model calculations.     

Excited 0+ states in 156,158,160,162 Gd

Excited K^π = 0⁺ states in ^{156,158,160,162} Gd isotopes are studied by using the pairing plus quadrupole model (PPQ). To determine the nature and the general trend of the properties of these states depending on the neutron number, B(E2), ρ²(E0) values and two‐nucleon transfer strengths are calculated. We observe that by means of the PPQ model, approximately 13‐14 0⁺ states can be obtained up to 3.3 MeV for the nuclei in question, where most of them are two‐quasiparticle (2qp) in character.     

Remeasurement of the lifetime of the 4 1 + -state of156Gd and recalculation of itsg-factor

The half-life of the 4 ₁ ⁺ -state of¹⁵⁶Gd has been remeasured by the delayed coincidence technique. The excellent time resolution which can now be achieved by use of small BaF₂ detectors allows a more reliable determination than with previously applied methods. The resultT _1/2(¹⁵⁶Gd,4 ₁ ⁺ )=108(2) ps is smaller than previously published data, but it fits well into the systematics of theB(E2) values of the rotational transitions of this nucleus. A recalculation of the previously measuredg-factor of the same state givesg(¹⁵⁶Gd,4 ₁ ⁺ ) =0.327(19). This value is still smaller than theg-factor of the 2 ₁ ⁺ state, but the magnitude of the reduction can now easier be interpreted by nuclear structure calculations.     

Description of multi-band structures in154Gd and156Gd on symmetry considerations

The observed similarities of the yrast band level energies of several pairs of lighter rare-earth even-even nuclei are indicative of a particle-hole type symmetry for nuclei withA =164±a. This feature is sought to be described in terms of the representations of theSU(7) group in the interacting Fermion picture.SU(3) reduction of this group leads to the prediction of characteristic multi-band structures in these nuclei. Detailed comparison of the single-parameter predictions of this scheme with the available experimental informations on the level schemes for the nuclei¹⁵⁴Gd and¹⁵⁶Gd reveals striking agreement between the theory and the experiments. The results are discussed in comparison with the predictions of the simple Interacting Boson Model.     

Gamma-ray spectra and positive parity bands in 158Gd

A Ge(Li)-NaI(Tl) pair spectrometer and a Ge(Li)-NaI(Tl) anti-Compton spectrometer were used to measure γ-rays from the reaction ¹⁵⁷Gd(n, γ)¹⁵⁸Gd. A detailed decay scheme for levels of ¹⁵⁸Gd was constructed up to an excitation energy of 2504 keV. Branching ratios for transitions from members of the positive parity bands to members of the ground state band were determined. It is shown that a single band-mixing parameter is not sufficient to explain the experimental results, and that even a four-band-mixing calculation does not provide satisfactory agreement. The binding energy of the last neutron is determined to be 7937.4±0.7 keV.     

g-Faktoren und Multipol-Mischungsverhältnisse in156Gd

By integral perturbedγ-γ-angular correlation the gyromagnetic ratios of a 2-quasi-particle state at 1,513 keV and the 4⁺ state of the ground state rotational band in¹⁵⁶Gd were measured, using sources prepared by¹⁵⁹Tb(γ, 3n) and¹⁵⁶Gd(d, 2n) reactions:g _{1;513 keV} ⁴⁺ =0.78±0.05;g _R ⁴⁺ =0.37±0.05. In addition we obtain the multipole mixing ratiosδ _{535 keV}(M2/E1)=?0.09±0.01;δ _{1,225 keV}(E2/M1)=+1.83±0.10 for the 535 keV and 1,225 keVγ-rays. The classification of the 1,513 keV state is discussed. The internal field of Gd in Tb metal at 77 °K was found to beH=(?192±16)kOe.     

Investigation of statistically perturbed angular correlations of154Gd and156Gd in different liquid sources

The statistical perturbations of γγ-angular correlations involving the first 2⁺ rotational state of¹⁵⁴Gd and¹⁵⁶Gd have been time differentially investigated. We used liquid sources of 3⁺ ions of Gadolinium in lN perchloric acid, 0.5 N and 1N hydrochloric acid, 1.3N and 2.6 N sulfuric acid. Influences of the various chemical surroundings on the ratio λ₄/λ₂ of the attenuation parameters have been found. A simultaneous measurement of the angular correlation of the 874 keV–123 keV cascade and the 2,098 keV–89 keV cascade of¹⁵⁴Gd and¹⁵⁶Gd, respectively, has been performed in perchloric solution. From the ratio of the attenuation parameters λ₂, obtained by this experiment, we have derived the ratio of the magneticg-factors of the first 2⁺ levels of these isotopes asg ¹⁵⁴/g ¹⁵⁶=1.11±0.08.     

Low-spin states in151Gd

The level structure of the 87-neutron nucleus¹⁵¹Gd has been investigated by studying the EC- andβ ⁺-decay of¹⁵¹Tb. Gamma-ray and conversion electron spectra as well as gamma-gamma coincidence spectra were measured by using semiconductor spectrometers and a high-capacity two-parameter recording system. The proposed decay scheme contains several new energy levels in¹⁵¹Gd, among them a 5^?/2 state at 427 keV. To explain the low-energy level structure, a small stable deformation is assumed for¹⁵¹Gd. Using a single-particle-plus-rotor model based on a generalized Woods-Saxon potential, complete mixing of the shells 1h _9/2, 2f _7/2 and separately 1i _13/2 is observed. By these mixings the correct level order and approximately correct excitation energies up to 1 MeV are reproduced.