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.     

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.     

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).     

Luminescent and scintillation properties of YAG:Dy and YAG:Dy,Ce single crystalline films

The paper is devoted to investigation of the luminescent properties of Dy³⁺ and Dy³⁺-Ce³⁺ doped single crystalline films (SCF) grown by LPE method from PbO–B₂O₃ flux. We have found that the YAG:Dy and YAG:Dy,Ce SCFs possess bright cathodoluminescence in the visible range and good scintillation figure of merit. For this reason LPE grown YAG:Dy and YAG:Dy,Ce SCF are proposed for different applications, namely, as cathodoluminescence screens or screens for microimaging. The Dy³⁺ co-doping can be also proposed for improvement of the scintillation efficiency of the Ce³⁺ doped garnet compounds in the SCF form due to Dy³⁺→ Ce³⁺ energy transfer and removing the trap related centers in the above RT range.     

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     

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.     

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.     

Selecting cold 2n transfer in 162Dy(116Sn,118Sn)160Dy

Cold 2n transfer has been studied using the reaction ¹⁶²Dy(¹¹⁶Sn,¹¹⁸Sn)¹⁶⁰Dy at energies in the vicinity of the Coulomb barrier. The experiment was performed at the Heidelberg-Darmstadt Crystal Ball spectrometer which was extended by 6 Compton suppressed Ge-detectors. It is demonstrated, that the direct population of intrinsically cold states in the deformed ¹⁶⁰Dy transfer product can be selected by identifying and suppressing excitations to states above the yrast line using the Crystal Ball. The probability for populating yrast states in the deformed ¹⁶⁰Dy nuclei in a 2n transfer reaction increases from 7% at grazing collisions up to ≈ 50% at large impact parameters, while the probability for populating the ground state in the spherical 2n transfer product ¹¹⁸Sn stays about constant at ≈ 45% for all measured impact parameters. Received: 4 September 1998     

The mass of the nucleus148Dy

Usingγγ coincidences theEC(K)/β ⁺ ratio for theβ decay¹⁴⁸Dy→¹⁴⁸Tb has been determined.¹⁴⁸Dy has been produced through the irradiation of⁹³Nb with 249 MeV⁵⁸Ni ions. The mass of¹⁴⁸Dy has been deduced. With the help of knownQα values the masses of¹⁵²Er,¹⁵⁶Yb,¹⁶⁰Hf and¹⁶⁴W have been obtained. The experimental masses are compared with different current mass formulae.     

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.     

Identification of a new isotope,168Dy

A previously unreported nuclide,¹⁶⁸Dy, has been identified and found to have a half-life of 8.5+-0.5 min. The activity was produced in the spontaneous fission of²⁵²Cf and transported via a He jet system to a rapid radiochemical separative facility where the Dy fraction was removed from the mixed fission products. The assignment of this activity to¹⁶⁸Dy decay was based on the presence of five γ rays in the chemically separated Dy fraction which were associated with the decay of an 8.5-min activity and on the observation of the grow-in and subsequent decay of the daughter, 2.98-min¹⁶⁸Ho, with approximately an 8-min half-life. The γ-ray emission probabilities have been determined.     

Protonh 2 11/2 and octupole excitations in148 66Dy82 and149 66Dy83

The yrast states of¹⁴⁸Dy and¹⁴⁹Dy have been studied by γ-ray and conversion electron measurements in (α, xn) and (¹⁶O,xn) reactions on enriched¹⁵²Gd and¹³⁵Ce targets. Level schemes to above 4 MeV for the two nuclei are reported. The πh ² _11/2 spectrum identified in¹⁴⁸Dy and the πh _11/2 effective chargee _eff=1.52±0.05e, derived from the measuredE2 transition rate between the (πh ² _11/2) 10⁺ and 8⁺ states, are discussed and compared with results for other two-particle nuclei. The yrast cascades in¹⁴⁸Dy and¹⁴⁹Dy continue above the (πh ² _11/2) 10⁺ and πh ² _11/2 vf _7/2) 27/2^? states by ～ 1 MeVE1 transitions de-exciting the lowest members of octupole multiplets built on these states. The energy shifts for the observed members of the πh ² _11/2 × 3^? multiplet are analyzed in terms of twoparticle-phonon exchange coupling using an empirical coupling strength extracted from the one valence particle nucleus¹⁴⁷Tb. The dominantvf _7/2×3^? character of low-lying 13/2⁺ isomers in¹⁴⁹Dy and otherN=83 nuclei is emphasized.     

High-spin states in neutron-rich Dy isotopes populated in deep-inelastic reactions

High-spin states in neutron-rich Dy isotopes, populated in deep-inelastic processes produced by the interaction of 234 MeV ³⁷Cl ions with a ¹⁶⁰Gd target, have been studied using the highly sensitive EUROBALL IV gamma-ray detector array. The previously known level schemes for ^{159,160,161,162}Dy have been extended to significantly higher spin ( ? 30?) and the i _13/2 band crossing in ¹⁵⁹Dy has been observed for the first time. The experimental results are discussed within the framework of cranked shell model and projected shell model calculations with particular reference to the observed delayed band crossing in ¹⁶²Dy. Received: 20 October 2000 / Accepted: 16 January 2001     

High-spin states in 155Dy and 154Dy from (12C,xn, γ) studies

Levels in ¹⁵⁵Dy and ¹⁵⁴Dy were studied using ${}^{146}\text{Nd}\text{(}{}^{12}\text{C}\text{, x}\text{n}\text{, γ)}$ reactions. Excitation functions between 57 MeV and 109 MeV, γ-angular distributions and γ-γ-time three dimensional coincidence relationships were determined. The most intense feature of the ¹⁵⁵Dy spectrum is a cascade of stretched E2 transitions between levels of the strongly mixed positiveparity band arising from the $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}\text{, N = 6}$ shell-model state. Several of the strong γ-rays associated with a 6 μs isomer are also observed and placed in this decay scheme with this $\text{11}\text{2}$^? isomeric state of ¹⁵⁵Dy at 233.4 keV. A less strongly populated rotational band is based on this $\text{11}\text{2}$^? [505] orbital. The available information on ¹⁵⁵Dy from this and previous studies is discussed to arrive at a consistent interpretation. Coriolis mixing calculations are performed for the positive parity band and compared with the experimental data. Additional transitions of the ground rotational band in ¹⁵⁴Dy are identified up to the level with spin 14⁺ (18⁺). For the spins higher than 14 “back-bending” occurs. Transitions from states of a β-vibrational band are confirmed.     

Emission spectra of MgSO4:Dy,MgSO4:Tm and MgSO4:Dy,Mn phosphors

MgSO₄:Dy, MgSO₄:Tm and MgSO₄:Dy,Mn thermoluminescence (TL) phosphors have been prepared and their emission spectra were measured using a linear heater and optical multichannel analyzer. Emission bands at about 480, 580 and 660 nm of MgSO₄ doped with Dy were observed in three dimension (3D) glow curve. Emission bands about 360, 460, and 660 nm were observed in a 3D glow curve of MgSO₄ doped with Tm. The emission spectra of MgSO₄:Dy and MgSO₄:Tm are attributed to the characteristic emission wavelengths from transitions of Dy³⁺ and Tm³⁺ respectively. The results show that the structures of traps in matrix materials determine the activation energy distribution and dopant energy levels of rare earth ions are related with the emission spectrum wavelengths of sulfate phosphors. The intensities of the glow peaks in both bands at about 480 and 580 nm in MgSO₄ doped Dy and Mn were dramatically reduced in comparison with that of MgSO₄ doped Dy except above 300°C. It means that the trapping structures of MgSO₄ :Dy phosphor has greatly been altered by the co-dopant Mn but no change is observed in wavelengths of the emission spectra.     

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.     

The search for Hyperdeformation in152Dy

Three experiments have been carried out to search for the existence of Hyperdeformed states (HD) in the nucleus¹⁵²Dy. These three experiments were designed to test different properties of the expected HD structures. As a result of these experiments no clear evidence for HD states in¹⁵²Dy has been observed.     

Possible two-phononβγ-vibration in 156Dy

The level structure of ¹⁵⁶Dy has been investigated with the (p, t) reaction at E_p = 29.9 MeV. A strong (7.7% of ground-state strength) transition is observed to a state at 1520 keV, assigned J^π = 2⁺. It is suggested that this state is the two-phonon βγ-vibration predicted by the theory of Davydov. Possible connections to the “super-band” in ¹⁵⁶Dy are discussed.     

Luminescence characteristics of Dy3+ activated Na 2Sr 2Mg (BO 3)2F 2: Dy 3+ phosphor

In this paper, we have reported a new Na ₂Sr ₂Mg (BO ₃)₂F ₂:Dy ³⁺ thermoluminescence (TL) phosphor prepared via the wet chemical method. Prepared phosphor was characterized by X-ray powder diffraction, photoluminescence (PL), TL and scanning electronmicroscopy techniques. The scanning electronmicroscopic image of Na ₂Sr ₂Mg (BO ₃)₂F ₂:Dy ³⁺ phosphor confirms the micron size of particles. Under the PL study, the characteristic emission spectrum of Dy ³⁺ corresponding to ⁴F _9/2→⁶H _15/2 (481 nm) and ⁴F _9/2→⁶H _13/2 (576 nm) transitions was observed. The TL property of the as prepared phosphor was also found to be good. TL intensity of Na ₂Sr₂Mg(BO ₃)F ₂:Dy ³⁺ phosphors at 0.99 kGy exposure of γ-irradiations was compared with standard CaSO ₄:Dy phosphor. It was seen that TL intensity of Na ₂Sr ₂Mg (BO ₃)₂F ₂: Dy ³⁺ phosphors is 1.1 times less compared with the standard CaSO ₄:Dy TL dosimeter phosphor. The kinetic parameters are also discussed in detail. The values of activation energy E (eV) and frequency factor S (s ^?1) were found to be 0.57 eV and 1.25×10⁶ s^?1, respectively.     

On the nature of the superband in156Dy

Superbands, responsible for the backbending in¹⁵⁶Dy and other N=90 and N=88 nuclei, are proposed to be alignedn(i_13/2)² bands, whereas it is argued that the recently discovered positive parity band in¹⁵⁶Dy withI ^π= (2⁺) up to 10⁺ members does not constitute the low spin extension of the superband.