Coulomb excitation studies of 160Dy, 162Dy and 164Dy

Coulomb excitation measurements with ¹⁶O and ⁴He projectiles have been performed on ¹⁶⁰Dy, ¹⁶²Dy, and ¹⁶⁴Dy. The ground-state rotational bands up through the 8⁺ member were observed in the ¹⁶O experiments. The measured excitation probabilities yield B(E2; I → I ?2) values which are generally in agreement with the rotational predictions except for the 6⁺ → 4⁺ values. In each nucleus, probabilities for exciting the 2⁺, 4⁺, and 6⁺ members of the γ-vibrational band were measured and compared with calculated results. The B (E2; 0⁺ → 2⁺γ) values were measured in experiments involving ⁴He ions. The K^π = 2^? octupole band was observed in each nucleus in addition to 1^? bands in ¹⁶⁰Dy and ¹⁶²Dy. Excitation probabilities were analyzed in an attempt to extract B(E3) values.     

Hyperfine-structure measurements on Dy161 and Dy163

In an atomic beam magnetic resonance experiment the hyperfine interaction constantsA andB of the⁵ I ₈ groundstate of Dy¹⁶¹ and Dy¹⁶³ were found to be Dy¹⁶¹:A=?(115.8±1)MHz, Dy¹⁶³:A=(162.9±0.6)MHz,B=(1102±15)MHz,B=(1150±20)MHz. Using an effective value for 〈r^?3〉, the magnetic moments and electric quadrupole moments of the Dy¹⁶¹ and Dy¹⁶³ nuclei were calculated to be Dy¹⁶¹:μ _I=?(0.47±0.09) n.m., Dy¹⁶³:μ _I=(0.66±0.13)n.m.,Q=(2.36±0.4)barns,Q=(2.46±0.4)barns.     

156Dy as the core of157Dy

The positive-parity energy levels in the¹⁵⁷Dy nucleus are analysed by means of the core-quasiparticle coupling model. The decoupled rotational band structure of the spectrum is reproduced by the theory. The collective components of the¹⁵⁷Dy levels are shown. The calculated pick-up and stripping spectroscopic factors are compared with experiment.     

NMR of Dy nuclei in ferromagnetic DyAl2 and Dy metal

The NMR spin echo of Dy nuclei in ferromagnetic DyAl₂ yields for the Dy¹⁶¹ hyperfine field constant, a=?845.2±0.3 MHz and quadrupolar splitting, 2P=420.0±0.3 MHz compared to a=?830.0±0.5 MHz and 2P= 387.8±0.5 MHz in ferromagnetic Dy metal. The different contributions to these parameters are discussed. A line, observed at 1273 MHz Dy metal, is attributed to Δm_I = 2 transition.     

Electromagnetic properties of high spin states in158Dy and164Dy

We present calculations of electromagnetic properties of¹⁵⁸Dy and¹⁶⁴Dy based on the solution of the self-consistent cranking model and approximate angular momentum projection technique developed earlier. The calculated values compare fairly well with the existing experimental data.     

The hyperfine structure and hyperfine anomaly of 161Dy and 163Dy

The hyperfine structure of ¹⁶¹Dy and ¹⁶³Dy for five transitions hasbeen measured with a tunable dye laser and a thermal velocity atomic beam. Values for the magnetic dipole and electric quadrupole coupling constants have been determined for the relevant excited states. The hyperfine anomaly parameters, Δ, which are extracted are interpreted in terms of available atomic wave functions.     

Magnetoelastic effects in Dy

Measurements have been made of the magnetic field dependence of C₄₄ for Dy in the magnetically ordered regime in fields of up to 8 tesla. The results are compared to the predictions of Southern and Goodings from magnetoelastic theory and found to be in fair agreement at 4.2 K, while at higher temperatures the theoretical estimates are much lower than the measured values.     

Mechanical properties of low porosity Dy123 bulks with different Dy211 content

Mechanical properties of low porosity Dy123 (DyBa₂Cu₃O_x) bulks with different Dy211 (Dy₂BaCuO₅) content were evaluated through bending tests and Vickers indentation tests of specimens cut from the bulks. The bending strength and the Young’s modulus of the low porosity bulks were higher than those of porous Dy123 bulks evaluated in the previous study. The bending strength of the low porosity bulks, which was decreased by the oxygen annealing, increased with increase of the Dy211 content. The fracture toughness of the area with uniform dispersion of the Dy211 particles was superior to that with low density of the Dy211 particles.     

Investigation of the reaction Dy164 (n, γ) Dy165

The level structure of Dy¹⁶⁵ has been investigated at the Karlsruhe research reactor using thermal neutron capture in Dy¹⁶⁴. The target was Dy₂O₃ enriched to 92.71% Dy¹⁶⁴. Neutrons were either monochromized by Bragg reflection from a lead crystal or transmitted through a bismuth single crystal filter. High-resolution measurements of the capture spectrum have been performed by means of a Ge(Li) 5-detector pair spectrometer and a Ge(Li) anti-Compton assembly. A large number of new lines has been observed. Cascade relationships were studied by using several techniques: a double coincidence apparatus with 4″ Ø×5″ NaI(Tl) detectors, a coincidence system containing a scintillation detector and a 34 cm³ Ge(Li)-diode as well as a two-parameter system involving the pair spectrometer (with NaI (Tl) as the primary detector) and a single 4″Ø×6″ NaI (Tl) counter. In the framework ofNilsson's model and simple microscopic pictures of vibrational states the results are consistent with the following spectroscopic interpretation: 0 keV, 7/2⁺[633]; 108.2 keV, 1/2^?[521]; 184.3 keV, 5/2″[512]; 533.5 keV, 5/2″ [523]; 538.6 keV, 7/2⁺[633] +Q₂₂; 570.3 keV, 5/2^?[512]+Q₂₂+1/2^?[510]; 573.6 keV, 3/2^? [521]+1/2^?[521]+Q₂₂; 1103.3 keV, 1/2^? [521]+Q₂₂+3/2^? [521]. For comparison preliminary results are given for the isotonic nucleus Yb¹⁶⁹.     

Decay scheme of155Dy

The simple and coincidence spectra of gamma radiation accompanying the decay of¹⁵⁵Dy were measured with Ge(Li) and scintillation detectors. The source was obtained as a daughter product of¹⁵⁵Ho. The intensity or the upper limit of intensity were determined for all, and the multipolarity for most of the observed transitions. The coincidence measurements served as a basis for the introduction of new levels at 250, 1062, 1068, (1494) and 1638 keV, and as a proof of the existence of the 891, 1155, 1665 and 1749 keV levels proposed earlier.The authors wish to express their thanks to RNDr. Z. Plajner for his unrestricted support and assistance during the experiments, to N. A. Lebedyev for the preparation of the sources, to Professor F. L. Shapiro for the loan of the measuring apparatuses in the Joint Nuclear Research Institute, and to RNDr. I. Rezanka for his help in the measurements.     

Beta decay of 157Dy

The decay of ¹⁵⁷Dy(T_1/2 = 8.14(4)h) is investigated. Spectra of γ-rays, internal conversion electrons and γ ? γ coincidences are measured. The 983.50 and 991.70 keV transitions show E0 admixtures. Our experimental results made it possible to extend substantially the decay scheme. From the coincidence relationships we established four new excited states of ¹⁵⁷Tb at 883.32, 895.06, 925.29, 970.38 keV and confirmed the 357.66 keV state. The levels at 1160.71 and 1318.62 keV are introduced from the energy balance. Tentative evidence is given for the existence of five new levels at 252.58, 327.65, 658.36, 793.52 and 922.69 keV. We assign Nilsson’s quantum characteristics to all introduced levels. The structure of the excited states of ¹⁵⁷Tb is discussed in terms of current nuclear models.     

β-delayed proton decays and spin assignments for 140Tb, 141Dy and 143Dy

The proton-rich isotopes ¹⁴⁰Tb and ¹⁴¹Dy were produced via the fusion evaporation reaction ⁴⁰Ca + ¹⁰⁶Cd. Their β-delayed proton decays were studied by p-γ coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, γ-transitions following the proton emission, as well as β-delayed proton branching ratios to the low-lying states in the grand-daughter nuclei were determined. Comparing the experimental data with statistical model calculations, the ground-state spins of ¹⁴⁰Tb and ¹⁴¹Dy were found to be consistent with 7 and 9/2, respectively. The configuration-constrained nuclear potential energy surfaces (NPES) of ¹⁴⁰Tb and ¹⁴¹Dy were calculated using the Woods-Saxon-Strutinsky method, which suggest the ground-state spins and parities of ¹⁴⁰Tb and ¹⁴¹Dy to be 7⁺ and 9/2^-, respectively. In addition, the configuration-constrained NPES of ¹⁴³Dy were calculated, which predict a 1/2⁺ ground state and a 11/2^- isomer with excitation energy of 198keV. These findings are consistent with our previous experimental data on ¹⁴³Dy reported in Eur. Phys. J. A 16, 347 (2003).     

Superdeformed states in rotating152Dy

The recently observed gamma-spectrum of¹⁵²Dy at angular momenta 25>~I>~60 is interpreted in terms of a strongly deformed shape isomer. A pronounced minimum is found for these angular momenta in the sum of liquid-drop energy (including rotational part) and shell-correction (calculated in the Nilsson model) of¹⁵²Dy. The general criteria for stability of this minimum against rotation are discussed.     

Dy̧namics of radiating electrons

A new formulation is given of the dynamical problem of a harmonically bound nonrelativistic electron with dipole coupling to the electromagnetic field in the radiation gauge, in a finite region of space. This formulation leads in a simple manner to an exact solution. An effective electron radius is introduced mathematically rather than physically. Inter alia it is found (i) that the proper mass renormalization shows up naturally, (ii) that the electron's quantum mechanics involves an ultraviolet divergence, and (iii) that the usual phenomenological radiation damping is predicted.     

Rotation-induced shape transitions in Dy nuclei

Lifetimes of states with spins up to 30? have been measured in the nuclei ¹⁵⁶Dy, ¹⁵⁷Dy, and ^ll58Dy using the recoil-distance technique together with inverse reactions of the type $\text{Mg}\text{(}{}^{136}\text{Xe}\text{, x}\text{n}\text{)}$. The applied method, which benefited from the high velocities of the fusion residues as well as from improvements of the recoil-distance technique, allowed us to determine lifetimes and feeding times down to 0.1 ps. Below the first backbending the resultant B(E2) values in the ground-state band of ^{156, 158}Dy increase faster with increasing rotational frequency than expected for rigid rotors, reaching values similar to those observed for the well-deformed neutron-rich Dy isotopes. In contrast to this, the E2-transition probabilities between high-spin states are clearly retarded. The retardation gradually evolves from the rotation alignment of nucléons and indicates deformation changes most likely towards a triaxial shape. From the analysis of the side-feeding times of the high-spin yrast states it could be furthermore deduced that the E2 component of the preyrast γ-decay stems from transitions along highly collective bands.     

High-spin structure of neutron-rich Dy isotopes

In view of recent experimental progress on production and spectroscopy of neutron-rich isotopes of Dy with mass number A =166 and 168, we have made theoretical investigations on the structure of high spin states of^164-170Dy isotopes in the cranked Hartree-Fock-Bogoliubov (CHFB) theory employing a pairingquadrupolehexadecapole model interaction. With the increase of neutron number the rotation alignment of the proton orbitals dominates the structure at high spins, which is clearly reflected in the spin dependence of the rotational g-factors. A particularly striking feature is the difference in the spin-dependent properties of¹⁶⁶Dy as compared to that of¹⁶⁴Dy