Coriolis coupling and electromagnetic properties of rotational bands in odd-A Yb nuclei

Influence of a Coriolis coupling on the properties of¹⁷³Yb has been studied using the quasi-particle-phonon model of Soloviev. The energy and structure of the rotational levels, reduced E 2 and M 1 transition probabilities and E 2/M 1 multipole mixing ratios have been calculated. A comparison between theory and experiment is on the whole successful.     

Nuclear orientation study of the decay of 171Lu

The levels and γ-ray transitions in ¹⁷¹Yb have been studied by radioactive decay of oriented ¹⁷¹ Lu. The orientation was produced using the hyperfine field in ferromagnetic gadolinium to polarize an ensemble of ¹⁷¹Lu nuclei at a temperature of 14mK. The directional distribution of the γ-rays was measured using high-resolution Ge(Li) detectors. Anisotropies of 30 γ-rays in ¹⁷¹Yb were measured. Multipole mixing ratios were deduced for most of the mixed γ-ray transitions and unambiguous spin assignments were made for several levels.The energy and structure of the rotational band levels, reduced E2 and M1 transition probabilities and E2/M1 mixing ratios were calculated using the semi-microscopic quasiparticle-phonon model with a Coriolis interaction. In general, good agreement is obtained between the theoretical predictions and experimental results.     

The change of sign of E2 and M1 matrix elements,and of δ-values of166Er at high spins

Calculations of the Dynamic Deformation Model for the E2/M1 mixing ratios for ψ-band to ground-band transitions in¹⁶⁶Er have been extended to higher spins (up to I=20). Previous comparisons with the experimental values and with the IBA-1 predictions, available at present up to spins 8 only, are also included for the sake of completeness. Additional comparison with the Frankfurt Model is also given. While all three models give reasonable magnitudes of the mixing ratios, only the DDM gives the sign changes at the correct spin values. Predictions are presented for additional sign changes of the mixing ratios, as well as those of the E2 and the M1 transition moments.     

Coriolis coupling and electromagnetic properties of rotational bands in odd-a Yb nuclei

Properties of the rotational bands in¹⁶⁷Yb are studied using the quasiparticle-phonon model with the Coriolis interaction included. The level energies,B(E2) andB(M1) values, E2/M1 mixing ratios, and magnetic moments are calculated. In particular, theB(E2) values and the E2/M1 mixing ratios measured by using delay coincidence and nuclear orientation methods, respectively, are well reproduced.Dedicated to Professor Ivan Úlehla on the occasion of his sixtieth birthday.     

Angular correlations in the decay of 233Pa to 233U

Gamma-gamma angular correlations have been measured for five cascades in the decay of ²³³Pa to ²³³U. E2/M1 multipole mixing ratios were deduced for five gamma transitions, based on the observed correlations, conversion coefficients, and model dependent calculations based on branching ratios. Nilsson-model calculations including Coriolis mixing give good agreement with the deduced values.     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

Vibrational band structure in 184W populated in the decay of 184Re

The decay of ^184mRe has been investigated through γ-ray and conversion electron studies. The band head of the K^π = 2^? octupole band has been established at 1130.0 keV. The E2/M1 mixing ratios of three transitions from the γ-vibrational band to the ground state band have been determined by angular correlation measurements. A mixing of El, M2 and E3 multipolarity has been derived for the 921 keV transition combining angular correlation and conversion electron data. A value B(E3, 0⁺ → 3^? = (25 ± 5) × 10⁴e² · fm⁶ was obtained from the measured E2/M1 mixing of the 91 keV 3^? → → 2^? transition and γ-branchings. The data are discussed in terms of the collective model taking into account band mixing.     

Angular-correlation study of the level scheme of 193Ir

The decay of ¹⁹³Os to ¹⁹³Ir has been studied by γγ angular correlations. Inconsistencies between previous angular correlations, internal conversion coefficients, and nuclear orientation angular distributions have been satisfactorily resolved by the present results. These data are used to derive a set of $\text{E2}\text{M 1}$ multipole mixing ratios of the transitions between low-lying states. The resulting electromagnetic transition moments are compared with calculations based on the Nilsson model with Coriolis mixing and on the interacting boson-fermion model.     

Spectroscopic properties of 237,239Pu fission isomers from self-consistent calculations

We have studied ^237,239Pu isomeric states: energy levels, M1 and E2 spectroscopic moments and reduced transition probabilities have been calculated within the rotor+quasi-particle model from self-consistently determined single-particle states. The electromagnetic properties of these states have been especially investigated. Without any ad hoc parameter adjustment, a very good reproduction of most of the known spectroscopic data is yieldedwhich assesses the predictive power of the whole approach.     

The M2 radiative widths of nuclear levels at about 7 MeV excitation

The M2 widths and M2/E1 mixing ratios in transitions of the form 1⁻¹ → 2⁺ from nuclear levels at about 7 MeV excitation in ⁷⁴Ge, ¹⁰⁰Mo, ¹¹²Cd and ¹⁸⁶W have been measured. The M2 widths are found to be about the same average magnitude as the M2 widths in nuclei with A < 40.     

EPM calculations of E2/M1 mixing ratios for even samarium isotopes 146–152Sm

The M1 operator and the E2/M1 mixing ratios, Δ(E2/M1), are discussed in the framework of the extended phonon projection model (EPM). The model is applied to ^{146, 148, 150, 152}Sm to describe their M1 properties. Comparison is made between the EPM, the consistent-Q formalism (CQF) of the basic interacting-boson approximation (IBA-1) and the experimental Δ(E2/M1) data. Both theoretical approaches give reasonably good results and parameter systematics.     

Low-spin levels in 136Ba studied via the (n,n'γ) reaction

Low-spin levels in ¹³⁶Ba have been studied by means of the (n, n'γ) reaction using reactor fast neutrons. Excited states up to an excitation energy of 2.8 MeV and with spin values up to 7 were found to be populated. Energies, intensities and angular distributions of γ-rays attributed to ¹³⁶Ba have been measured.In addition to the confirmation of known level characteristics the angular distribution data resulted in new unique spin assignments for 7 levels (2 for the levels at 2080.0 keV, 2128.8 keV and 2484.7keV, 3 for those at 2390.8, 2399.8 and 2431.0 keV as well as 0⁺ for the 2141.3 keV level). Furthermore E2/M1 multipole mixing ratios were determined for the most intensive mixed γ-transitions.     

Gamma-gamma directional correlation measurements in192Os

E2/M1 mixing ratios of transitions in¹⁹²Os have been determined by the gammagamma directional correlation technique. The results are: δ(484.5 keV)= ?10±1, δ(283.3 keV)= ?3.8± 0.7 and δ(201.3 keV)= ?4.6±1.     

Microscopic study of α + 14C molecular states in the 18O spectrum

The properties of the ¹⁸O nucleus are investigated with antisymmetrized α + ¹⁴C_g.s. wave functions. Quadrupole moments, rms radii, and reduced α-widths as well as E1 and E2 transitions probabilities are calculated. Comparison with experiment shows that transition probabilities involving molecular states are overestimated by the model, and indicates that a mixing of α + ¹⁴C¹ configurations should be considered.     

Electromagnetic transitions in the ground-state rotational band of159Tb

The ground-state band of¹⁵⁹Tb has been Coulomb excited up to spin 23/2 by 151-MeV⁴⁰Ar ions. The lifetimes of the 9/2 to 23/2 levels have been determined by combining results obtained with the RD and DSA methods, theE2/M1 mixing ratios for ΔI=1 transitions have been measured using angular correlation techniques and the branching ratios for the levels up to spin 17/2 have been determined. The energies of the levels and the reducedM1 andE2 transition probabilities for their decay have been compared with the predictions of the rotational model, without and with ΔK=1 admixtures. No satisfactory agreement could be achieved for all available experimental data simultaneously.     

The nuclear structure of 151Pm in the low excitation region < 1 MeV

The level scheme of ¹⁵¹Pm populated by the β-decay of 12 min ¹⁵¹Nd has been studied using Ge(Li) detectors as singles and coincidence γ-ray spectrometers. Most of the new γ-rays have been included in a partial level scheme of ¹⁵¹Pm involving four new levels. Angular correlation measurements on the 170.752–255.678 keV and 170.752–138.882 keV cascades have been made with the result A₂ = 0.088±0.005 and ?0.02 – +0.05, respectively. A PAC measurement on the 170.752–255.678 keV cascade has yielded the g-factor of the 255.676 keV level as g = 1.18 ±0.16. A Nilsson-model calculation including Coriolis coupling has been made and the experimental level energies have been well reproduced by the Nilsson orbitais [413]↓, [411]↑, [420]↑, [532]↑, [541]↑ and [550]↑. Theoretical transition rates, E2/M1 mixing ratios, branching ratios and g-factors are in good agreement with experimental values.     

The E2 strength distribution in 6Li studied by the (e,d0) reaction

Angular distributions have been measured for the ⁶Li(e, d₀) reaction in the excitation energy range 10–28 MeV. The differential cross sections are decomposed into E1 and E2 components on the basis of a simple cluster model. The E2 strength deduced using a virtual photon spectrum is spread over the entire energy region studied. This strength reflects isoscalar E2 excitations in ⁶Li. The E1 strength, which results from isospin mixing, shows no significant structure.     

The spin of the 2,198 keV level in74Ge and multipole mixing ratios of gamma transitions in the decay of74As

Directional-correlation measurements of several cascades in the⁷⁴As decay have been made with a NaI — Ge(Li) detectors system. In the⁷⁴Ge the following cascades were measured: 608–596 keV, 994–1,204 keV, 994-(608)-596 keV and 887-596 keV. The corresponding results give a unique spin assignment of 2 for the 2,198 keV level and determine theE2/M 1 mixing ratios ofδ(608)=3.4±0.4 andδ(994)=?(2.8 ± 0.2). In the⁷⁴Se it was measured the 635-635 keV cascade. The result obtained assigned the spin of the 1,270 keV level as 2 and fixed the E2/M1 mixing ratio of δ(635)=?(2.6 ± 0.2). Also aγ-intensity study has been made to determine the branching ratios of the transitions that deexcite the 1,270 keV level in⁷⁴Se. From these data aI(635)/I(1,270)=12.5 ± 5.0 is obtained.