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Modelling crystal-field interaction for f-elements in LaCl{sub 3}

Description: The results of crystal field calculations in the framework of exchange charge model (ECM) are reported for trivalent lanthanide and actinide ions doped into LaCl{sub 3}. Whereas the scalar strength of the model crystal field parameters are consistent with that previously determined by fitting the experimental data, the sign of the second-order parameter is found to be negative, in contrast to previous reports. The contribution from long-range electrostatic interactions exceeds that from the nearest neighboring ligands and leads to the negative sign of the second-order crystal field parameter. Other interaction mechanisms including overlap, covalence, and charge exchange are less important to the second order parameter, but dominate the fourth-and sixth-order parameters. This work provides a consistent interpretation of the previously controversial experimental results for both lanthanide and actinide ions in this classical host.
Date: September 1, 1997
Creator: Zhorin, V.V. & Liu, G.K.
Partner: UNT Libraries Government Documents Department

Level Densities and Radiative Strength Functions in 170,171Yb

Description: Level densities and radiative strength functions in {sup 171}Yb and{sup 170}Yb nuclei have been measured with the {sup 171}Yb({sup 3}He, {sup 3}He{prime}{gamma}){sup 171}Yb and {sup 171}Yb({sup 3}He,{alpha}{gamma}){sup 170}Yb reactions. A simultaneous determination of the nuclear level density and the radiative strength function was made. The present data adds to and is consistent with previous results for several other rare earth nuclei. The method will be briefly reviewed and the result from the analysis will be presented. The radiative strength function for {sup 171}Yb is compared to previously published work.
Date: June 9, 2003
Creator: Agvaanluvsan, U; Schiller, A; Becker, J A; Berstein, L A; Guttormsen, M; Mitchell, G E et al.
Partner: UNT Libraries Government Documents Department

Radiative Strength Functions and Level Densities

Description: Radiative strength functions and level densities have been extracted from primary {gamma}-ray spectra for {sup 27,28}Si, {sup 56,57}Fe, {sup 96,97}Mo, and several rare earth nuclei. An unexpectedly strong ({approx} 1 mb MeV) resonance at 3 MeV in the radiative strength function has been observed for well-deformed rare earth nuclei. The physical origin of this resonance and its connection to the scissors mode is discussed.
Date: August 28, 2002
Creator: Schiller, A; Becker, J A; Bernstein, L A; Voinov, A; Guttormsen, M; Hjorth-Jensen, M et al.
Partner: UNT Libraries Government Documents Department

Deformed proton emitters.

Description: The mechanisms of proton radioactivity from deformed rare earth nuclei are discussed and preliminary results on the fine structure decay of {sup 131}Eu are presented.
Date: February 17, 1999
Creator: Carpenter, M. P.; Cizewski, J. A.; Davids, C. N.; Davinson, T.; Fotiades, N.; Henderson, D. J. et al.
Partner: UNT Libraries Government Documents Department

Octupole effects in the lanthanides

Description: Arrays of Anti-Compton Spectrometer enabled systematic investigations of octupole correlations in the neutron-rich lanthanides. The studies mostly confirm the theoretical expectations of moderate octupole deformation at medium spins in nuclei from this region but in some cases predictions deviate from the experiment. In cesium isotopes strong octupole effects are predicted but not observed and new measurements for {sup 139}Xe suggest octupole effects stronger than expected. Systematics of excitation energy of the 31 states excitations, updated in the present work for Xe isotopes, indicates the N=85 and Z=54 lines as borders for strong octupole correlations. Systematic of electric dipole moment, upgraded in the present work for Ca and Ce isotopes confirms the Z=54 limit and adds new information about local canceling of electric dipole moment at the N=90 neutron number.
Date: October 22, 1999
Creator: Urban, W.; Rzaca-Urban, T.; Phillips, W. R.; Durell, J. L.; Leddy, M. J.; Smith, A. G. et al.
Partner: UNT Libraries Government Documents Department

Nuclear states and shapes at high spin. [Good review]

Description: As angular momentum is added to a nucleus, the balance of forces acting upon it to determine its shape, moment of inertia, mode of rotation, and type of level structure may undergo a series of changes. At relatively low spins a deformed nucleus will rotate collectively, and one may see the effect of Coriolis antipairing in gradually increasing the moment of inertia. Around spin 12 to 16 h-bar there may be an abrupt change (backbending) when a pair of high-j nucleons unpairs and the nucleons align with the axis of rotation; this process allows the nucleus to slow its collective rotation. This process, the start of a sharing of angular momentum between single-particle motion and the collective rotation, gives a lower total energy and corresponds to a change toward triaxiality in the shape of the nucleus. At much higher spins discrete ..gamma..-ray transitions can no longer be observed. This is the regime of continuum spectra; all the information on these high-spin states (to 65 h-bar) is contained in these continuum cascades. Knowledge is accumulating on how to study these spectra, experimentally and theoretically, and new techniques offer promise of revealing a great deal of information about the shapes and properties of very high spin states. 71 references, 34 figures.
Date: August 1, 1980
Creator: Diamond, R.M.
Partner: UNT Libraries Government Documents Department

Low lying electric dipole excitations in nuclei of the rare earth region

Description: From many experiments with low energy photon scattering on deformed rare earth nuclei we have obtained detailed information about the distribution of electric dipole strength below 4 MeV. Apart from some weaker transitions between 2 and 4 MeV we observed one, and sometimes two, very strong El-groundstate transitions around 1.5 MeV in all examined nuclei. They arise from the de-excitation of the bandheads of the (J{sup {pi}},K)=(l{sup {minus}},0) and (J{sup {pi}},K)=(l{sup {minus}},1) octupole vibrational bands. It is shown that the decay branching ratios and the absolute transition strengths of these states can be reproduced rather well with an improved T(El)-operator in the sdf-Interacting Boson Model. Another class of octupole states has been investigated in the region of the semimagic nucleus {sup 142}Nd. Here a quintuplet of collective excitations around 3.5 MeV is expected due to the coupling of the 3{minus}-octupole vibration with the 2+-quadrupole vibration. We performed photon scattering experiments on the odd A neighboring nucleus {sup 141}Pr and found first evidence for the existence of 3{sup {minus}}{circle_times}2+{circle_times}particle-states.
Date: October 1, 1992
Creator: von Brentano, P.; Zilges, A.; Herzberg, R. D.; Zamfir, N. V.; Kneissl, U.; Heil, R. D. et al.
Partner: UNT Libraries Government Documents Department

Workshop on nuclear structure at moderate and high spin: Slide report

Description: The workshop was scheduled to coincide with the beginning of operation of a number of large arrays of Compton-suppressed germanium detectors. The workshop was divided into 14 sessions containing 3 presentations each. The topics of these sessions were superdeformation, heavy rare earths, single-particle configurations, band termination, continuum properties, light rare-earths, new techniques, high temperatures, transfer reactions, transition region, shapes, lifetimes, and moments. This publication consists of the slides used in all of the presentations at the workshop.
Date: October 1, 1986
Partner: UNT Libraries Government Documents Department

Radiative Strength Functions in 172Yb below 8 Me V

Description: We have measured prompt {gamma} rays after thermal and resonant neutron capture in {sup 171}Yb. The {gamma} rays were measured with three high resolution ({approx}3 keV) and high efficiency (two {approx}80% Ge(HP) and one {approx}200% segmented Clover) detectors. We have obtained singles and two-fold coincidence spectra as function of neutron energy using the time-of-flight technique. Two-fold coincidences where the summed energy adds up to the neutron binding energy B{sub n} or to B{sub n} minus the energy of the first excited stated ({approx}79 keV) will be used to determine the multipolarity of the pygmy resonance in {sup 172}Yb. This pygmy resonance is a resonant structure in the radiative strength function around {approx}3 MeV in deformed rare earth nuclei [1]. The following goals were met: (1) We have shown the feasibility of prompt, high-resolution {gamma} spectroscopy at FP14 after thermal as well as resonant neutron capture. (2) Online analysis shows that sufficient statistics ({approx}7000 counts) are expected in each of the two relevant peaks in the summed-energy spectrum. Analysis of the experiment is in progress. It still remains to show that the multipolarity of the pygmy resonance can be determined experimentally from two-step cascade intensities.
Date: February 6, 2002
Creator: Schiller, A; Becker, J A; Bernstein, L A; Garrett, P E; Hill, T S; McNabb, D P et al.
Partner: UNT Libraries Government Documents Department

M1-E2 mixing ratios of gamma-ground transitions in /sup 168/Er

Description: The L subshell ratios of four ..gamma..-g transitions in /sup 168/Er have been measured with the high resolution, iron, ..beta..-spectrometer at the Institut Laue-Langevin. The reduced M1-E2 mixing ratios are not consistent with the values predicted by Warner on the basis of IBA-1. It may be possible to explain the results in IBA-2 in terms of the ..delta..K = 1 mixing of the gamma-band and the pure antisymmetric states such as the 1+ isovector mode.
Date: September 10, 1984
Creator: Gelletly, W.; Warner, D.D.; Colvin, G.C. & Schreckenbach, K.
Partner: UNT Libraries Government Documents Department

Unexpected structure in the E2 quasicontinuum spectrum of /sup 154/Dy

Description: The evolution of the ..gamma.. quasicontinuum spectrum with neutron number has been investigated in the sequence of dysprosium isotopes /sup 152,154,156/Dy. The three nuclei display a pronounced collective E2 component. In /sup 154/Dy this component shows an unexpected splitting into two distinct parts, signifying a structural change along the ..gamma.. cascade. The E2 and statistical components can be reproduced in simple ..gamma.. cascade calculations; in /sup 152/Dy and /sup 156/Dy only rotational bands were included, whereas in /sup 154/Dy additional vibration-like transitions were required to reproduce the two E2 peaks. 11 refs., 2 figs.
Date: January 1, 1988
Creator: Holzmann, R.; Khoo, T.L.; Ma, W.C.; Ahmad, I.; Dichter, B.K.; Emling, H. et al.
Partner: UNT Libraries Government Documents Department

Properties of nuclei at very high spin

Description: Nuclear structure at very high spins involves an interplay between collective (often rotational) and noncollective (individual particle alignment) behavior. The new techniques for studying ..gamma..-ray energy correlations promise to give detailed information about both of these aspects of nuclear behavior up to the very highest spins that can be populated. 17 figures.
Date: September 1, 1980
Creator: Stephens, F.S.
Partner: UNT Libraries Government Documents Department

Understanding nuclear quadrupole deformations

Description: A simple ansatz that ''Nuclei, not too near closed shells, are as deformed as they can be within a single major shell'' appears to quantitatively reproduce the variations of the quadrupole moments and hence the deformations of nuclei. 6 refs., 3 figs.
Date: January 1, 1989
Creator: Raman, S.
Partner: UNT Libraries Government Documents Department

Use of high-pressure ion exchange for the production of gadolinium-153. Status report

Description: A large high-pressure ion-exchange column, which had been designed for the separation of gadolinium from europium, was tested in the laboratory. Good separations were obtained. Subsequently, columns of the same design were installed in a hot cell and have been used successfully for the separation of gadolinium-153 from irradiated natural europium. The gadolinium-153 production achieved using these columns is substantially greater than that achieved using the previous process. Rapid damage of the resin is a problem and frequent resin changes are required.
Date: April 1, 1986
Creator: Posey, J.C.
Partner: UNT Libraries Government Documents Department

High spin isomers in /sup 153/Er

Description: Energy levels of /sup 153/Er were investigated with four NaI detectors in coincidence with a Ge(Li) detector. The existence of two long-lived high-spin isomers was confirmed, and their positions and decays were established. 1 figure. (RWR)
Date: January 1, 1980
Creator: Horn, D; Young, G R; Lister, C J & Baktash, C
Partner: UNT Libraries Government Documents Department

Novel, convenient, and nonpersistent radiotracer for environmental and energy applications

Description: A newly-available radioisotopic system, /sup 172/Hf-/sup 172/Lu, has excellent potential for tracer applications in which nuclear data acquisition must be accomplished in real time. The 6.7-day half-life of /sup 172/Lu is sufficient for a large fraction of tracer experiments, and should allow the direct incorporation of /sup 172/Lu into tests that have traditionally utilized much longer-lived radionuclides. Since /sup 172/Lu is the daughter component of a radioisotope generator, however, its effective shelf-life is determined by the half-life of its 1.9-year /sup 172/Hf parent. Consequently, the frequency of isotope procurement need not be any more extensive than investigators would normally be accustomed to. Discussion relevant to isotope production, generator operation, and nuclide acquisition is presented in this paper.
Date: March 12, 1984
Creator: Grant, P.M.
Partner: UNT Libraries Government Documents Department

Isotope shift in /sup 151,153/Eu/sup +/ from high-precision hyperfine structure measurements

Description: Isotope shift in the two stable isotopes of Eu/sup +/ has been obtained for four optical transitions between the states 4f/sup 7/(/sup 8/S/sup 0/)5d /sup 9/D/sub J//sup 0/ and 4f/sup 7/(/sup 8/S/sub 7/2//sup 0/)6p/sub 3/2/;J' using high-precision hyperfine structure measurements in a collinear laser and slow ion beam (1.35 keV) apparatus. 5 refs., 2 figs., 1 tab.
Date: January 1, 1987
Creator: Sen, A. & Childs, W.J.
Partner: UNT Libraries Government Documents Department

Phenomena at very high spins. [Approx. 70 h-bar; review]

Description: The present talk has three parts: first, a discussion of current ideas about the physics of very high spin states; second, some comments about noncollective behavior up to the highest spins where it is known, approx. 40 h; and finally, a presentation of the newest method for studying collective behavior up to spins of 60 to 70 h. The intention is that the overview presented in the first part will be sufficiently broad to indicate the relationship of the noncollective and collective behavior discussed in the other parts, and to provide some understanding of the compromise in behavior that seems to occur at the very highest spins. 13 figures.
Date: March 1, 1980
Creator: Stephens, F.S.
Partner: UNT Libraries Government Documents Department

Moessbauer effect of europium metal under pressure

Description: The pressure dependence of the magnetic hyperfine field and of the isomer shift of /sup 151/Eu in europium metal has been studied in a diamond anvil pressure cell at low temperatures. In the pressure range 0-12 GPa at 44/sup 0/K (T/sub N/ = 90/sup 0/K), the magnetic hyperfine field changes from -22 T to -8 T while the isomer shift increases from -7.3 to -3.8 mm s/sup -1/ relative to a SmF/sub 3/ source. The changes are interpreted as indicative of a pressure-driven intermediate valence state causing a reduced magnetic moment in Eu. Intermediate valence and magnetic order coexist over the range of pressures studied.
Date: September 1, 1986
Creator: Taylor, R.D. & Farrell, J.N.
Partner: UNT Libraries Government Documents Department

M1 transitions between collective levels and F-spin purity

Description: M1 transitions between low-lying collective levels in deformed nuclei are described within the IBM-2 framework. This is done by a special choice of the Hamiltonian which allows a simultaneous fit of energies, E2 and M1 transitions. Finally, the results are interpreted using the F-spin concept. 12 refs., 4 tabs.
Date: January 1, 1987
Creator: von Brentano, P.; Frank, W.; Gelberg, A.; Harter, H.; Krips, W.; Casten, R.F. et al.
Partner: UNT Libraries Government Documents Department

Microscopic analysis of angular momentum projected HFB-states in terms of interacting bosons

Description: Angular momentum- and number-projected Hartree-Fock-Bogoliubov (HFB) wavefunctions for transitional and deformed Rare Earth nuclei are analyzed in terms of Fermion pairs coupled to angular momenta L = 0(S), 2(D), 4(G), ... The Fermion space is truncated to contain only S-D or S-D-G pairs. The variation is carried out before and after angular momentum projection and with different truncations. The influence of the truncation on physical quantities such as moments of inertia, quadrupole moments or pair transfer matrix elements is discussed. 21 references.
Date: December 1, 1984
Creator: Ring, P. & Pannert, W.
Partner: UNT Libraries Government Documents Department