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Results from GAMMASPHERE in the A {approx} 80 mass region

Description: We present recent results obtained with GAMMASPHERE for nuclei in the A{approx}80 mass region. These studies have concentrated on a systematic study of superdeformed bands and their transitional quadrupole moments. Normally-deformed rotational bands in a series of even-even T{sub z} = 1 nuclei were also investigated to probe the possible influence of the np pairing on the structure of their yrast bands.
Date: August 2, 1996
Creator: Rudolph, D.; Baktash, C. & Brinkman, M.J.
Partner: UNT Libraries Government Documents Department

Discrete-line transitions from superdeformed to yrast states in {sup 194}Hg and {sup 192}Hg

Description: Discrete-line {gamma}-ray decay from superdeformed (SD) to yrast states in {sup 194,192}Hg has been studied with the Gammasphere spectrometer. The previously established decay for the yrast SD band of {sup 194}Hg has been characterized further. In addition, one-step decays have been observed for {sup 194}Hg SD band 3, which fixes the excitation energy and spin of the last observed level of this band at E* = 7.455 MeV, J = 11{Dirac_h}. So far no direct decays from superdeformed to yrast states have been observed in {sup 192}Hg or in {sup 194}Hg band 2, a result which is consistent with fluctuations of the transition strengths.
Date: December 31, 1996
Creator: Hackman, G.; Khoo, T.L. & Ackermann, D.
Partner: UNT Libraries Government Documents Department

First measurement of the degree of fragmentation of the decay out cascade from the superdeformed yrast band in {sup 192}Hg

Description: The decay spectrum of the yrast superdeformed band in {sup 192}Hg comprises a quasicontinuum with discrete lines ranging from 1 to 3.2 MeV. The intensity fluctuations of this quasicontinuum give information on the degree of fragmentation of the decay cascades and on the effect of pairing correlations on the level density {rho}(U) in the normal deformed well (0 < U < U{sub SD}).
Date: December 1, 1996
Creator: Lopez-Martens, A.; Hannachi, F. & Schueck, C.
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

The quasi-continuum of gamma rays following the decay of superdeformed bands in the Hg region

Description: The quasi-continuum of the spectrum associated with the decay-out of the yrast superdeformed band in {sup 194}Hg has been extracted. It has for the first time been possible to compare the spin and excitation energy determined from the analysis of the quasi-continuum {gamma} rays to the exact result obtained from the on-step linking transitions.
Date: December 31, 1996
Creator: Lauritsen, T.; Khoo, T.L. & Janssens, R.V.F. and others
Partner: UNT Libraries Government Documents Department

Superdeformation in the mass A {approximately} 80 region

Description: A new island of superdeformed nuclei with major-to-minor axis ratio of 2:1 has recently been discovered in the A {approximately} 80 medium-mass region, confirming the predictions for the existence of a large SD gap at particle number N,Z {approximately} 44. The general properties of more than 20 bands observed so far will be reviewed here, and compared with those of the superdeformed bands in the heavier nuclei.
Date: December 31, 1996
Creator: Baktash, C.
Partner: UNT Libraries Government Documents Department

Decay of superdeformed bands

Description: One of the major challenges in the study of superdeformation is to directly connect the large number of superdeformed bands now known to the yrast states. In this way, excitation energies, spins and parities can be assigned to the levels in the second well which is essential to establish the collective and single-particle components of these bands. This paper will review some of the progress which has been made to understand the decay of superdeformed bands using the new arrays including the measurement of the total decay spectrum and the establishment of direct one-step decays from the superdeformed band to the yrast line in {sup 194}Hg. 42 refs., 5 figs.
Date: December 1995
Creator: Carpenter, M. P.; Khoo, T. L. & Lauritsen, T.
Partner: UNT Libraries Government Documents Department

Superdeformation and hyperdeformation at high spin

Description: A short review of theoretical and experimental studies of superdeformation and hyperdeformation is presented. Recent results, based on calculations carried out in a four dimensional deformation space, are presented. Very extended nuclear shapes ranging in mass from A=150 to A=200 are discussed.
Date: August 1, 1995
Creator: Chasman, R.R.
Partner: UNT Libraries Government Documents Department

Superdeformed shapes and configurations in thallium nuclei

Description: Superdeformation studies in {sup 189,191,192}Tl at Gammasphere are discussed. New results on {sup 191}Tl are the observation of interband transitions between the signature partner E2 bands and the measurement of an average quadrupole moment (Q{sub 0} = 18 {+-} 1 eb) for these superdeformed structures. These data enable them to derive absolute M1 strengths and confirm that the 81st proton occupies the [642]5/2 orbital. Tentative data for one superdeformed sequence in {sup 189}Tl are consistent with the prediction of a decrease in quadrupole deformation for the lightest nuclei at the limit of this island of superdeformation.
Date: September 1997
Creator: Reviol, W.; Mueller, W. F. & Riedinger, L. L.
Partner: UNT Libraries Government Documents Department

Around the back-bend in an excited {sup 150}Gd superdeformed band

Description: The excited superdeformed band (band 5) in {sup 150}Gd has a discontinuity (back-bend) in the smooth variation of gamma-ray energy with spin at around 1 MeV. It has been established that the band also has a decay branch that is probably a continuation of band 5 below the back-bend. Gamma-rays have been identified which link band 5 with the yrast superdeformed band in {sup 150}Gd.
Date: December 1, 1996
Creator: Twin, P. J.; Ertuerk, S. & Beausang, C. W.
Partner: UNT Libraries Government Documents Department

How close are hyperdeformed states to the scission point?

Description: The HFB method with the Gogny force is used to study the effects of reflection asymmetry at I = 0{h_bar} on the barriers separating superdeformed and hyperdeformed minima from fission in the {sup 176}W and {sup 168}Yb nuclei. The fission barrier for the HD minimum is reduced by 5 MeV in {sup 176}W when reflection asymmetry is taken into account.
Date: December 1, 1996
Creator: Robledo, L.M.; Egido, J.L. & Chasman, R.R.
Partner: UNT Libraries Government Documents Department

Self-consistent methods in nuclear structure physics

Description: The authors present a very brief description of the Hartree Fock method in nuclear structure physics, discuss the numerical methods used to solve the self-consistent equations, and analyze the precision and convergence properties of solutions. As an application, they present results pertaining to quadrupole moments and single-particle quadrupole polarizations in superdeformed nuclei with A {approximately} 60.
Date: November 1, 1997
Creator: Dobaczewski, J.
Partner: UNT Libraries Government Documents Department

Tunneling from super- to normal-deformed minima in nuclei.

Description: An excited minimum, or false vacuum, gives rise to a highly elongated superdeformed (SD) nucleus. A brief review of superdeformation is given, with emphasis on the tunneling from the false to the true vacuum, which occurs in the feeding and decay of SD bands. During the feeding process the tunneling is between hot states, while in the decay it is from a cold to a hot state. The {gamma} spectra connecting SD and normal-deformed (ND) states provide information on several physics issues: the decay mechanism; the spin/parity quantum numbers, energies and microscopic structures of SD bands; the origin of identical SD bands; the quenching of pairing with excitation energy; and the chaoticity of excited ND states at 2.5-5 MeV. Other examples of tunneling in nuclei, which are briefly described, include the possible role of tunneling in {Delta}I = 4 bifurcation in SD bands, sub-barrier fusion and proton emitters.
Date: January 8, 1998
Creator: Khoo, T. L.
Partner: UNT Libraries Government Documents Department

Superdeformation in the A=150 and A=190 regions.

Description: Superdeformation has been established for over a decade in the mass 150 region and nearly as long in the A=190 region. The first measurements directed at nuclei in these regions concentrated on mapping out the superdeformed (SD) islands by identifying SD rotational bands in {gamma}-ray coincidence data. These early studies provided new insights into the physics of superdeformation, but also raised unexpected issues. The new gamma-ray arrays (Gammasphere, Eurogam/Euroball and Gasp) have provided a wealth of new data on properties of SD states in these two mass regions. This paper highlights some of the more recent results from the large arrays which have addressed the outstanding issues in the field, namely, {Delta}I = 4 staggering, identical bands, SD vibrational bands, and questions about the feeding into and the decay out of the SD well.
Date: December 1, 1998
Creator: Carpenter, M. P.
Partner: UNT Libraries Government Documents Department

Decay out of the yrast superdeformed band in {sup 191}Hg.

Description: The excitation energies and spins of the yrast superdeformed band in {sup 191}Hg have been determined by analyzing the quasicontinuum spectrum connecting the superdeformed and normal-deformed states. The results from this analysis, combined with that given by one-step decay lines, give confident assignments of the spins and energies of the yrast superdeformed band in {sup 191}Hg.
Date: March 24, 1999
Creator: Sien, S.; Reiter, P.; Khoo, T.; Lauritsen, T.; Carpenter, M. P.; Ahmad, I. et al.
Partner: UNT Libraries Government Documents Department

Nuclear structure research. Annual progress report

Description: The most significant development this year has been the realization of a method for estimating EO transition strength in nuclei and the prediction that the de-excitation (draining) of superdeformed bands must take place, at least in some cases, by strong EO transitions. A considerable effort has been devoted to planning the nuclear structure physics that will be pursued using the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge. A significant effort has been devoted to HRIBF target development. This is a critical component of the HRIBF project. Exhaustive literature searches have been made for a variety of target materials with emphasis on thermodynamic properties. Vapor pressure measurements have been carried out. Experimental data sets for radioactive decays in the very neutron-deficient Pr-Eu and Ir-Tl regions have been under analysis. These decay schemes constitute parts of student Ph.D. theses. These studies are aimed at elucidating the onset of deformation in the Pr-Sm region and the characteristics of shape coexistence in the Ir-Bi region. Further experiments on shape coexistence in the neutron-deficient Ir-Bi region are planned using {alpha} decay studies at the FMA at ATLAS. The first experiment is scheduled for later this year.
Date: July 31, 1995
Creator: Wood, J.L.
Partner: UNT Libraries Government Documents Department

The multiplicity of shapes in Tl nuclei

Description: The results of experiments on rotational bands in light Tl nuclei are used to indicate the richness of shape phenomena in the vicinity of a closed proton shell. Rotational bands associated with normal prolate and oblate shapes as well as with a superdeformed shape are observed. 34 refs., 4 figs.
Date: December 1995
Creator: Riedinger, L. L.; Reviol, W. & Lewis, J. M.
Partner: UNT Libraries Government Documents Department

Lifetime measurements and identical SD bands in the A=190 and A=150 regions

Description: The lifetimes of states in Superdeformed (SD) bands in {sup 192, 194}Hg, {sup 151,152}Dy, and {sup 151}Tb have been measured using the Doppler shift attenuation method. Intrinsic quadrupole moments Q{sub 0} have been extracted for SD bands in these nuclei. It was found that the quadrupole moments for the ``identical`` SD bands in these nuclei are the same. In the A = 150 region, changes were found in the Q{sub 0} values as a function of the number of high-N intruder orbitals. Changes are present also for excited SD bands with the same high-N content. Recent calculations account for most of the observations in the A = 150 region.
Date: September 3, 1996
Creator: Moore, E. F.; Nisius, D. & Janssens, R. V. F.
Partner: UNT Libraries Government Documents Department

Systematic description of superdeformed bands in the Mass-190 region

Description: Superdeformed bands for the mass-190 region are described by the Projected Shell Model. Even-even, odd mass and odd-odd nuclei are equally well described. Good agreement with available data for all isotopes studied is obtained. Our,calculation of electromagnetic properties and pairing correlations provides an understanding of the observed gradual increase of dynamical moments of inertia with angular momentum observed in many bands in this mass region.
Date: December 31, 1996
Creator: Sun, Y.; Guidry, M. & Zhang, J.
Partner: UNT Libraries Government Documents Department

The Structure of Nuclei Far from Stability

Description: From among a number of important nuclear structure results that have emerged from our research program during the past few years, two stand out as being of extra significance. These are: (a) the identification of a diabatic coexisting structure in {sup 187}Au which arises solely from differences in proton occupation of adjacent oscillator shells, and (b) the realization of a method for estimating EO strength in nuclei and the resulting prediction that the de-excitation of superdeformed bands may proceed, in some cases, by strong EO transitions.
Date: February 25, 1999
Creator: Zganjar, E.F.
Partner: UNT Libraries Government Documents Department

Lifetime measurements and dipole transition rates for superdeformed states in {sup 190}Hg.

Description: The Doppler-shift attenuation method was used to measure life-times of superdeformed (SD) states for both the yrast and the first excited superdeformed band of {sup 190}Hg. Intrinsic quadruple moments Q{sub 0} were extracted. For the first time, the dipole transition rates have been extracted for the inter-band transitions which connect the excited SD band to the yrast states in the second minimum. The results support the interpretation of the excited SD band as a rotational band built on an octupole vibration.
Date: March 24, 1999
Creator: Amro, H.
Partner: UNT Libraries Government Documents Department

Octupole effects at super and normal deformation.

Description: This presentation deals with recent results on the onset of octupole collectivity in superdeformed nuclei of the A {approx} 190 and A {approx} 150 regions as well as in actinide nuclei at normal deformation. It is shown that most of the properties of these negative parity sequences can be understood in terms of Random Phase Approximation (RPA) calculations, although the observations in some Pu isotopes continue to be a challenge to interpret.
Date: June 6, 2002
Creator: Janssens, R. V. F.
Partner: UNT Libraries Government Documents Department

Lifetime measurements and the issue of identical superdeformed bands

Description: Lifetime measurements for superdeformed bands in {sup 151,152}Dy and {sup 192,194}Hg have been performed at GAMMASPHERE using the Doppler shift attenuation method. The transition quadrupole moments for several bands in these nuclei have been extracted from an analysis of centroid shift data. Of particular interest are the quadrupole moments associated with the so-called `identical` superdeformed bands in these nuclei. A preliminary analysis indicates that the values of the quadrupole moments in the identical bands are equal within experimental errors. This results suggests that the deformations associated with the identical bands are very similar.
Date: 1995-12~
Creator: Moore, E. F.; Nisius, D. & Janssens, R. V. F.
Partner: UNT Libraries Government Documents Department

Evidence for octupole vibration in the superdeformed well of {sup 109}Hg

Description: An excited superdeformed (SD) band has been observed in {sup 19O}Hg which decays to the lowest-energy (yrast) SD band rather than to the less deformed states as observed in most known SD bands in the A{approximately}150 and A{approximately}190 regions. The band exhibits properties which are in good agreement with predictions of collective octupole vibrations in the SD well of {sup 19O}Hg.
Date: July 1, 1994
Creator: Crowell, B.; Janssens, R. V. F.; Carpenter, M. P.; Ahmad, I.; Harfenist, S.; Henry, R. G. et al.
Partner: UNT Libraries Government Documents Department