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Nuclear moments of inertia at high spins

Description: Nuclei with highest angular momentum are discussed. The production of high spin states, and the basic ideas associated with high spin physics are reviewed. Recent developments from continuum ..gamma..-ray studies are presented: the measurement of different average moments of inertia gives new information on the interplay between collective and single particle aspects at high spins. Finally, the exciting possibility of resolving the continuum spectra with new detector systems is examined. 8 references.
Date: December 1, 1983
Creator: Deleplanque, M.A.
Partner: UNT Libraries Government Documents Department

Nuclear moments of inertia at high spin

Description: The competition between collective motion and alignment at high spin can be evaluated by measuring two complementary dynamic moments of inertia. The first, I band, measured in ..gamma..-..gamma.. correlation experiments, relates to the collective properties of the nucleus. A new moment of inertia I/sub eff/ is defined here, which contains both collective and alignment effects. Both of these can be measured in continuum ..gamma..-ray spectra of rotational nuclei up to high frequencies. The evolution of ..gamma..-ray spectra for Er nuclei from mass 160 to 154 shows that shell effects can directly be observed in the spectra of the lighter nuclei.
Date: October 1, 1982
Creator: Deleplanque, M.A.
Partner: UNT Libraries Government Documents Department

Test of {Delta}I = 2 staggering in the superdeformed bands of {sup 194}Hg

Description: The presence of {Delta}I = 2 staggering in the three known superdeformed bands of {sup 194}Hg has been reexamined in a new experiment with Gammasphere. A relative accuracy of better than 30 eV was achieved for most transition energies. No statistically significant oscillations in the transition energies were found for band 1 while staggering patterns were observed in bands 2 and 3. The statistical significance of the observed effects was analyzed. The patterns display some similarities with expectations based on a band crossing picture, even though such a picture cannot reproduce the observations in a straightforward way. No evidence was found for additional superdeformed bands in {sup 194}Hg which could account for possible band-crossings.
Date: June 5, 1996
Creator: Kruecken, R.; Deleplanque, M.A.; Lee, I.Y. & Asztalos, S.
Partner: UNT Libraries Government Documents Department

Test of {Delta}I = 2 staggering in the superdeformed bands of {sup 194}Hg

Description: Superdeformed (SD) states in {sup 194}Hg were populated in {sup 150}Nd({sup 48}Ca,4n) using a 201 MeV {sup 48}Ca beam from the 88- inch cyclotron. A high statistics experiment was done to test for the previously reported evidence for a {Delta}I = 2 staggering in the three SD bands in {sup 194}Hg. The transition energies were determined with a precision of at least 60 eV for most transitions. From this improvement, we cannot confirm evidence for an extended regular {Delta}I = 2 staggering in any of the three SD bands of {sup 194}Hg. However, we observe deviations from a smooth reference in the SD bands 2 and 3 which differ from previous results. Oscillation patterns of the {gamma}-ray energies that can be induced by a simple band crossing or level shift are discussed. Even though such level shifts would explain the observed effects, other experimental signatures, such as a crossing band, are needed to fully understand the results of the present work; no such band was found.
Date: November 1996
Creator: Kruecken, R.; Deleplanque, M. A. & Hackman, G.
Partner: UNT Libraries Government Documents Department

NUCLEAR SHAPES AT HIGH ANGULAR MOMENTUM

Description: Multiplicities as a function of {gamma}-ray energy have been measured for continuum {gamma}-ray spectra produced in argon- and calcium-induced reactions. A peak sometimes occurs in the multiplicity spectrum, indicating a correlation between {gamma}-ray energy and multiplicity (spin). This correlation can be explained by rotational motion of the nucleus, suggesting basically prolate nuclear shapes. Absence of structure in the multiplicity spectrum is interpreted to indicate non-collective motion, and hence spherical or oblate shapes.
Date: December 1, 1977
Creator: Deleplanque, M.A.; Lee, I.Y.; Stephens, F.S.; Diamond, R.M. & Aleonard, M.M.
Partner: UNT Libraries Government Documents Department

Gross shell structure of moments of inertia

Description: Average yrast moments of inertia at high spins, where the pairing correlations are expected to be largely absent, were found to deviate from the rigid-body values. This indicates that shell effects contribute to the moment of inertia. We discuss the gross dependence of moments of inertia and shell energies on the neutron number in terms of the semiclassical periodic orbit theory. We show that the ground-state shell energies, nuclear deformations and deviations from rigid-body moments of inertia are all due to the same periodic orbits.
Date: July 1, 2002
Creator: Deleplanque, M.A.; Frauendorf, S.; Pashkevich, V.V.; Chu, S.Y. & Unzhakova, A.
Partner: UNT Libraries Government Documents Department

Nuclear Science Division, Annual report, October 1, 1988--December 31, 1990

Description: This report contains short papers of research conducted in the following areas: Low energy research program; bevalac research program; ultrarelativistic research program; nuclear theory program; nuclear data evaluation; and, 88-inch cyclotron operations.
Date: April 1, 1991
Creator: Poskanzer, A.M.; Deleplanque, M.A.; Firestone, R.B. & Lofdahl, J.B. (eds.)
Partner: UNT Libraries Government Documents Department

EVIDENCE FOR ANGULAR MOMENTUM FRACTIONATION IN 86Kr-INDUCED REACTIONS ON 107,109Ag, 165Ho AND 197Au

Description: Gamma-ray multiplicities have been measured as a function of the light-fragment atomic number Z{sub 3} for the above reactions. The events associated with sequential fission of the heavy fragment were distinguished from binary events by means of a triple coincidence. The failure of the measured y-multiplicities for deep-inelastic collisions to rise with decreasing Z{sub 3}, according to the rigid-rotation limit, appears more likely to be associated with a selective population of the low Z fragments by the lower {ell}-waves rather than to an incomplete relaxation of the rotational energy.
Date: October 1, 1977
Creator: Aleonard, M.M.; Wozniak, G.J.; Glassel, P.; Deleplanque, M.A.; Diamond, R.M.; Moretto, L.G. et al.
Partner: UNT Libraries Government Documents Department

Order-to-chaos transition in rotational nuclei

Description: The authors have studied the narrow (valley-ridge) structure in the {gamma}-ray spectrum following a heavy-ion fusion reaction that produces several ytterbium nuclei. The intensity of this structure can be quantitatively related to the average chaotic behavior in these nuclei and they have traced this behavior from nearly fully ordered to nearly fully chaotic.
Date: May 13, 2004
Creator: Stephens, F.S.; Deleplanque, M.A.; Lee, I.Y.; Macchiavelli, A.O.; Ward, D.; Fallon, P. et al.
Partner: UNT Libraries Government Documents Department

Searching for E(5) behavior in nuclei

Description: The properties of even-even nuclei with 30 {le} Z {le} 82, A {ge} 60 have been examined to find examples displaying the characteristics of E(5) critical-point behavior for the shape transition from a spherical vibrator to a triaxially soft rotor. On the basis of the known experimental state energies and E2 transition strengths, the best candidates that were identified are {sup 102}Pd, {sup 106,108}Cd, {sup 124}Te, {sup 128}Xe, and {sup 134}Ba. The closest agreement between experimental data and the predictions of E(5) is for {sup 128}Xe and for the previously suggested example of {sup 134}Ba. It is proposed that {sup 128}Xe may be a new example of a nucleus at the E(5) critical point.
Date: January 1, 2004
Creator: Clark, R.M.; Cromaz, M.; Deleplanque, M.A.; Descovich, M.; Diamond, R.M; Fallon, P. et al.
Partner: UNT Libraries Government Documents Department

Damping in Yb nuclei

Description: In a mixture of three Yb nuclei, we find the rotational damping widths vary from 180 keV at 1.1 MeV {gamma}-ray energy to 290 keV at 1.5 MeV, and the average compound damping widths (or spreading widths) vary from 40 keV at 1.1 MeV {gamma}-ray energy to 60 keV at 1.3 MeV. The simulations also suggest extensive motional narrowing.
Date: July 1, 2002
Creator: Stephens, F.S.; Deleplanque, M.A.; Lee, I.Y.; Ward, D.; Fallon, P.; Cromaz, M. et al.
Partner: UNT Libraries Government Documents Department

First in-beam. gamma. -ray study of sup 67 As

Description: Excited states of the neutron-deficient nucleus {sup 67}As were populated using the {sup 40}Ca({sup 32}S,{alpha}p){sup 67}As and the {sup 40}Ca({sup 33}S,{alpha}pn){sup 67}As reactions at bombarding energies between 95 and 110 MeV. We present a tentative level scheme for {sup 67}As, derived from {gamma}-{gamma} coincidence studies in conjunction with measurement of evaporated charged particles and neutrons.
Date: January 1, 1990
Creator: Lang, T.F.; Moltz, D.M.; Reiff, J.E.; Batchelder, J.C.; Ognibene, T.J.; Cerny, J. et al.
Partner: UNT Libraries Government Documents Department

Population of Nuclei Via 7Li-Induced Binary Reactions

Description: The authors have investigated the population of nuclei formed in binary reactions involving {sup 7}Li beams on targets of {sup 160}Gd and {sup 184}W. The {sup 7}Li + {sup 184}W data were taken in the first experiment using the LIBERACE Ge-array in combination with the STARS Si {Delta}E-E telescope system at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. By using the Wilczynski binary transfer model, in combination with a standard evaporation model, they are able to reproduce the experimental results. This is a useful method for predicting the population of neutron-rich heavy nuclei formed in binary reactions involving beams of weakly bound nuclei formed in binary reactions involving beams of weakly bound nuclei and will be of use in future spectroscopic studies.
Date: August 8, 2005
Creator: Clark, Rodney M.; Phair, Larry W.; Descovich, M.; Cromaz, Mario; Deleplanque, M.A.; Fall on, Paul et al.
Partner: UNT Libraries Government Documents Department

Population of Nuclei Via 7Li-Induced Binary Reactions

Description: The authors have investigated the population of nuclei formed in binary reactions involving {sup 7}Li beams on targets of {sup 160}Gd and {sup 184}W. The {sup 7}Li + {sup 184}W data were taken in the first experiment using the LIBERACE Ge-array in combination with the STARS Si {Delta}E-E telescope system at the 88-Inch Cyclotron of the Lawrence Berkeley National Laboratory. By using the Wilczynski binary transfer model, in combination with a standard evaporation model, they are able to reproduce the experimental results. This is a useful method for predicting the population of neutron-rich heavy nuclei formed in binary reactions involving beams of weakly bound nuclei and will be of use in future spectroscopic studies.
Date: August 9, 2005
Creator: Clark, R M; Phair, L W; Descovich, M; Cromaz, M; Deleplanque, M A; Fallon, P et al.
Partner: UNT Libraries Government Documents Department

Deducing the 237U(n,f) cross-section using the Surrogate Ratio Method

Description: The authors have deduced the cross section for {sup 237}U(n,f) over an equivalent neutron energy range from 0 to 20 MeV using the Surrogate Ratio method. A 55 MeV {sup 4}He beam from the 88 Inch Cyclotron at Lawrence Berkeley National Laboratory was used to induce fission in the following reactions: {sup 238}U({alpha},{alpha}{prime}f) and {sup 236}U({alpha},{alpha}{prime}f). The {sup 238}U reaction was a surrogate for {sup 237}U(n,f) and the {sup 236}U reaction was used as a surrogate for {sup 235}U(n,f). Scattered alpha particles were detected in a fully depleted segmented silicon telescope array (STARS) over an angle range of 35{sup o} to 60{sup o} with respect to the beam axis. The fission fragments were detected in a third independent silicon detector located at backward angles between 106{sup o} and 131{sup o}.
Date: December 29, 2005
Creator: Burke, J T; Bernstein, L A; Escher, J; Ahle, L; Church, J A; Dietrich, F S et al.
Partner: UNT Libraries Government Documents Department

Very extended shapes in the A~;110 region

Description: High-angular-momentum states in {sup 108}Cd were populated via the {sup 64}Ni({sup 48}Ca,4n) reaction at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. A rotational band has been observed with a dynamic moment of inertia and deduced lower limit of the quadrupole moment suggesting a major-to-minor axis ratio larger than 1.8:1, placing it among the most deformed structures identified in any nucleus, to date.
Date: September 12, 2001
Creator: Clark, R.M.; Fallon, P.; Gorgen, A.; Cromaz, M.; Deleplanque,M.A.; Diamond, R.M. et al.
Partner: UNT Libraries Government Documents Department

Aspects of the coriolis interaction in U235

Description: We have performed three separate experiments at LBNL's 88-Inch Cyclotron over a period of several years in which {sup 235}U (thick target) was Coulomb-excited. It involved stand-alone experiments with Gammasphere and with the 8PI Spectrometer using {sup 136}Xe beams at 720 MeV, and a CHICO-Gammasphere experiment with an {sup 40}Ar beam at 180 MeV. In addition to extending the known negative-parity bands to high spin, we have assigned levels in some seven positive-parity bands which are in some cases (e.g. [631]1/2, [624]7/2 and [622]5/2) strongly populated by E3 excitation. The CHICO data has been analyzed to extract E2 and E3 matrix elements from the observed yields. Additionally, many E1 and M1 matrix elements could be extracted from the {gamma}-ray branching ratios.
Date: January 1, 2005
Creator: Ward, D.; Clark, R.M.; Cromaz, M.; Deleplanque, M.A.; Diamond, R.M.; Fallon, P. et al.
Partner: UNT Libraries Government Documents Department

In-beam gamma-ray spectroscopy of target fragmentation

Description: Fragmentation reactions, typically performed at energies {approx}E/A>50 MeV, produce neutron-rich nuclei but leave little angular momentum in the residues. In this work we have examined the product distribution and angular momentum input for a {sup 12}C beam at 30 MeV/A on a thick (40 mg/cm{sup 2}) target of {sup 51}V, testing the feasibility of in-beam gamma-ray spectroscopy study of target fragments at this lower energy. This technique allows the study of some neutron-rich nuclei to moderate spins, complementing the beam fragmentation studies.
Date: October 6, 2004
Creator: Rodriguez-Vieitez, E.; Lee, I.Y.; Ward, D.; Fallon, P.; Clark, R.M.; Cromaz, M. et al.
Partner: UNT Libraries Government Documents Department

Very extended shapes in 108Cd: evidence for the occupation of 'hyper-intruder' orbitals

Description: High-spin states in {sup 108}Cd were studied following the reaction {sup 64} Ni({sup 48}Ca,4n) at a beam energy of 207 MeV. Gamma rays were detected using the Gammasphere array. Two rotational bands have been observed at very high angular momentum. Measurements of fractional Doppler shifts yielded lower limits for the quadrupole moments and showed that the observed structures are at least as deformed as the superdeformed structures e.g. in the A {approx} 150 region, and possibly exceed a 2:1 axis ratio. The existence of very extended shapes has been predicted by cranked Strutinsky calculations, and recent projected shell model calculations suggest that the {pi}i{sub 13/2}hyper-intruder orbital is occupied in these newly observed bands.
Date: July 1, 2002
Creator: Gorgen, A.; Clark, R.M.; Fallon, P.; Cromaz, M.; Deleplanque, M.A.; Diamond, R.M. et al.
Partner: UNT Libraries Government Documents Department

Very elongated nuclei near A = 194

Description: A {gamma}-ray cascade in {sup 191}Hg of 12 members with average energy spacing 37 keV and Q{sub t} {equals} 18(3)eb was reported by Moore, and coworkers in 1989. This was the first report of very elongated nuclei (superdeformation) in this mass region. Since then, some 25 {gamma}-ray cascades have been observed in 11 (slightly neutron deficient) Hg, Pb and Tl nuclei. The bands have similar dynamic moments-of-inertia. Some nuclei exhibit multiple bands, and the backbending phenomena has been observed. Level spins can be obtained from comparison of transition energies to rotational model formulas. Selected bands (in different nuclei) have equal transition energies (within 0.1%). Alignment in integer multiples of {h bar} has been observed. Properties of these bands will be described. 27 refs., 3 figs.
Date: October 1, 1990
Creator: Becker, J.A.; Henry, E.A.; Yates, S.W.; Wang, T.F.; Kuhnert, A. (Lawrence Livermore National Lab., CA (USA)); Brinkman, M.J. et al.
Partner: UNT Libraries Government Documents Department

Superdeformation in the Hg-Tl-Pb region

Description: Superdeformation in the Hg-Tl-Pb region is discussed, with concentration on the experimental results. At least twenty-five superdeformed bands are known in this region, providing much new data to test theoretical calculations. 22 refs., 5 figs.
Date: October 1, 1990
Creator: Henry, E.A.; Becker, J.A.; Yates, S.W.; Wang, T.F.; Kuhnert, A. (Lawrence Livermore National Lab., CA (USA)); Brinkman, M.J. et al.
Partner: UNT Libraries Government Documents Department

Analysis of high-multiplicity gamma-ray events

Description: A significant improvement in the measured peak-to-background ratio of highly-correlated gamma-ray cascades can be achieved through the use of high-multiplicity gamma-ray coincident events. We studied this effect using data from the {sup 176}Yb({sup 22}Ne,6n){sup 192}Hg reaction at a beam energy of 122 MeV using HERA at the LBL 88-Inch cyclotron facility. An enriched set of all four- and higher-fold coincidences was culled from these data. 4 refs., 1 fig., 1 tab.
Date: October 1, 1990
Creator: Brinkman, M.J.; Cizewski, J.A. (Rutgers--the State Univ., New Brunswick, NJ (USA). Dept. of Physics and Astronomy); Manatt, D.R.; Becker, J.A.; Henry, E.A.; Roy, N. (Lawrence Livermore National Lab., CA (USA)) et al.
Partner: UNT Libraries Government Documents Department

Level spin and moments of inertia in superdeformed nuclei near A = 194

Description: Experimental transition energies in the superdeformed (SD) bands near A = 190 are least-squares fit to rotational model formulae in order to extract level spin. The data set includes 16 SD bands, which show no evidence of either irregular behavior near the bottom of the bands or abrupt angular momentum alignment at low {Dirac h}{omega}. The 9 transitions lowest in energy in each band are well described by the formulae. The fitted spin of the final state in the {gamma}-ray cascade is within {plus minus}0.1{Dirac h} of an integer or half-odd integer for 13 of the bands. The weight of the evidence suggests that meaningful level spins corresponding to these transitions can be inferred. The moment of inertia at {omega} = 0 is correlated, with I = 88.3(5){Dirac h}{sup 2}/MeV and I = 93.4(5){Dirac h}{sup 2}/MeV for the strong and weak bands, respectively. 19 refs., 2 figs., 2 tabs.
Date: April 1, 1990
Creator: Becker, J.A.; Roy, N.; Henry, E.A.; Yates, S.W.; Kuhnert, A. (Lawrence Livermore National Lab., CA (USA)); Draper, J.E. et al.
Partner: UNT Libraries Government Documents Department