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Anharmonic vibrator description of collective nuclei

Description: It is shown that a simple anharmonic vibrator model can account for the properties of yrast states in collective nuclei, as well as the quasi-band states built on the {gamma}-vibration or on the O{sub 2}{sup +} state. This description extends from nearly harmonic vibrator nuclei to pure rotor nuclei and encompasses both energies and B(E2) values. It survives both ``horizontal`` and ``vertical`` perspectives on the data of nuclear physics and offers a challenge to microscopic theories of nuclear structure.
Date: July 1, 1995
Creator: Casten, R.F. & Zamfir, N.V.
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

Level densities and gamma-ray strength functions in 170,171,172-Yb

Description: Level densities and radiative strength functions in {sup 171}Yb and {sup 170}Yb nuclei have been measured using the {sup 171}Yb({sup 3}He{sup 3}He{gamma}){sup 171}Yb and {sup 171}Yb({sup 3}He,{alpha}{gamma}){sup 170}Yb reactions. New data on {sup 171}Yb are compared to a previous measurement for {sup 171}Yb from the {sup 172}Yb({sup 3}He,{alpha}{gamma}){sup 171}Yb reaction. Systematics of level densities and radiative strength functions in {sup 170,171,172}Yb are established. The entropy excess in {sup 171}Yb relative to the even-even nuclei {sup 170,172}Yb due to the unpaired neutron quasiparticle is found to be approximately 2k{sub B}. Results for the radiative strength function from the two reactions lead to consistent parameters characterizing the ''pygmy'' resonances. Pygmy resonances in the {sup 170,172}Yb populated by the ({sup 3}He,{alpha}) reaction appear to be split into two components for both of which a complete set of resonance parameters are obtained.
Date: July 28, 2004
Creator: Agvaanluvsan, U; Schiller, A; Becker, J; Bernstein, L; Garrett, P; Guttormsen, M et al.
Partner: UNT Libraries Government Documents Department

Review of alpha-decay data from doubly-even nuclei

Description: Alpha-decay data from doubly-even nuclei throughout the periodic table are reviewed and evaluated. From these data, nuclear radius parameters are calculated by using the Preston formula for {alpha}- decay probabilities. The radius parameters for each element behave rather regularly as a function of neutron number. The show minima at the major closed shells, increase sharply for parents just above the closed shells, and decrease smoothly toward the next shell closure. The same trend is observed for {alpha} reduced widths calculated using the Rasmussen formalism. Any irregularity or large departure from this behavior indicates probable incorrect input data. This systematic behavior can also be utilized to estimate partial half- lives.
Date: September 1, 1996
Creator: Akovali, Y. A.
Partner: UNT Libraries Government Documents Department

Valence proton-neutron interaction strengths from double binding energy differences

Description: Empirical p-n interaction strengths have been extracted from experimental mass data using double-difference binding energy equations. The especially strong interactions for self-conjugate nuclei will be discussed as well as microstructure found for deformed and in doubly magic regions. Valence correlation Schemes provide a basis to comment on the stability of medium mass near-drip-line nuclei and superheavy elements.
Date: 1996-10~
Creator: Brenner, D. S.; Foy, B. D.; Warner, D. D.; Zamfir, N. V. & Casten, R. F.
Partner: UNT Libraries Government Documents Department

A primer on rotational collective enhancements in even-even nuclei

Description: The enhancement of the level density for deformed nuclei relative to the level density in spherical nuclei is calculated. The qualitative behavior of the enhancement factor as a function of excitation energy is explained, and a prescription for a more quantitative description of this behavior is suggested. The results presented here can be found elsewhere in the literature, however the treatments of this topic are dispersed in the literature, are often terse, and require some familiarity with disparate branches of physics. The emphasis of this paper is on step-by-step derivations of the physics and mathematics used in the calculation of level densities and rotational enhancement factors. Pertinent techniques from thermodynamics and group theory are introduced. Appendices provide detailed introductions to the principal mathematical tools.
Date: July 15, 2004
Creator: Younes, W
Partner: UNT Libraries Government Documents Department

Shell-model Monte Carlo studies of nuclei

Description: The pair content and structure of nuclei near N = Z are described in the frwnework of shell-model Monte Carlo (SMMC) calculations. Results include the enhancement of J=0 T=1 proton-neutron pairing at N=Z nuclei, and the maxked difference of thermal properties between even-even and odd-odd N=Z nuclei. Additionally, a study of the rotational properties of the T=1 (ground state), and T=0 band mixing seen in {sup 74}Rb is presented.
Date: February 1, 1997
Creator: Dean, D.J.
Partner: UNT Libraries Government Documents Department

Shell-model Monte Carlo calculations near N = Z

Description: The pairing and structure of nuclei near N = Z is described in the framework of shell-model Monte Carlo (SMMC) calculations. Principal results include the enhancement of J=0, T=1 proton-neutron pairing at N=Z nuclei, and the marked difference of thermal properties between even-even and odd-odd N=Z nuclei. Additionally I will present a study of the rotational properties for the T=1 (ground state), and T=0 band mixing seen in {sup 74}Rb.
Date: October 1, 1996
Creator: Dean, D.J.
Partner: UNT Libraries Government Documents Department

New signatures for phase/shape transitional regions

Description: The energies of low-spin yrast states, E(4{sub 1}{sup +}) and E(2{sub 1}{sup +}), and the transition probabilities, B(E2; 2{sub 1}{sup +} {yields} 0{sub 1}{sup +}), which are among the most revealing and easiest to measure observables of collectivity, show remarkable global correlations that provide new signatures to identify particular structures.
Date: July 1, 1993
Creator: Zamfir, N. V.; Casten, R. F.; Zhang, J. Y. & Brenner, D. S.
Partner: UNT Libraries Government Documents Department

F-spin purity of 2{sub 1}{sup +} states in even-even nuclei

Description: A procedure is proposed by which upper limits to the F-spin purity of 2{sub 1}{sup +} states in even-even nuclei can be estimated by an analysis of experimental g-factors. The procedure, applied to 17 nuclei with 46{le}Z{le}78, shows that F<F{sub max} admixture up to 10% are not uncommon. A systematic behavior with Z is also observed.
Date: September 1, 1993
Creator: Wolf, A.; Scholten, O. & Casten, R. F.
Partner: UNT Libraries Government Documents Department

Effective interactions, elementary excitations, and transport in the helium liquids

Description: Polarization potentials, the self-consistent fields which describe the primary consequences of the strong atom-atom interaction in the helium liquids, are developed for liquid /sup 4/He and /sup 3/He. Emphasis is placed on the common physical origin of the effective interactions in all helium liquids, and the hierarchy of physical effects (very short-range atomic correlations, zero point motion, and the Pauli principle) which determine their strength is reviewed. An overview is then given of the application of polarization potential theory to experiment, including the phonon-maxon-roton spectra of /sup 4/He and /sup 3/He-/sup 4/He mixtures, the phonon-maxon spectrum of normal and spin-polarized /sup 3/He, and the transport properties of superfluid /sup 4/He and of normal and spin-polarized /sup 3/He.
Date: January 1, 1986
Creator: Pines, D.
Partner: UNT Libraries Government Documents Department

Application of atomic vapor laser isotope separation to the enrichment of mercury

Description: Workers at GTE/Sylvania have shown that the efficiency of fluorescent lighting may be markedly improved using mercury that has been enriched in the /sup 196/Hg isotope. A 5% improvement in the efficiency of fluorescent lighting in the United States could provide a savings of approx. 1 billion dollars in the corresponding reduction of electrical power consumption. We will discuss the results of recent work done at our laboratory to develop a process for enriching mercury. The discussion will center around the results of spectroscopic measurements of excited state lifetimes, photoionization cross sections and isotope shifts. In addition, we will discuss the mercury separator and supporting laser mesurements of the flow properties of mercury vapor. We will describe the laser system which will provide the photoionization and finally discuss the economic details of producing enriched mercury at a cost that would be attractive to the lighting industry.
Date: September 1, 1986
Creator: Crane, J.K.; Erbert, G.V.; Paisner, J.A.; Chen, H.L.; Chiba, Z.; Beeler, R.G. et al.
Partner: UNT Libraries Government Documents Department

Nuclear structure studies of transitional nuclei. Progress report, October 1, 1979-August 31, 1980. [Univ. of Kentucky, Lexington]

Description: Systematic investigations of the nuclear level structures of stable heavy transitional nuclei are being performed by (n,n&#x27;..gamma..) reaction spectroscopy. Detailed ..gamma..-ray excitation functions and angular distributions permit characterization of low-lying states, with particular emphasis on understanding collective excitations of both positive and negative parity. Questions regarding nuclear shapes, deformation effects, and the applicability of various nuclear models to these nuclei have been addressed. Completed studies of /sup 194/Pt and /sup 198/Pt reveal significant structural differences between these nuclei, and have led to studies of other transitional nuclei as the next step in a comprehensive examination of this mass region. Cross section systematics for the (n,n&#x27;..gamma..) reaction are being developed and, where possible, ..gamma..-ray studies have been complemented by neutron detection time-of-flight measurements. 6 figures, 1 table.
Date: January 1, 1980
Creator: Yates, S.W.
Partner: UNT Libraries Government Documents Department

ENDF-201: ENDF/B-VI summary documentation

Description: Responsibility for oversight of the ENDF/B Evaluated Nuclear Data file lies with the Cross Section Evaluation Working Group (CSEWG), which is comprised of representatives from various governmental and industrial laboratories in the United States. Individual evaluations are provided by scientists at several US laboratories, including significant contributions by scientists from all over the world. In addition, ENDF/B-VI includes for the first time complete evaluations for three materials that were provided from laboratories outside the US. All data are checked and reviewed by CSEWG, and the data file is maintained and issued by the National Nuclear Data Center at Brookhaven National Laboratory. The previous version of the library, ENDF/B-V, was issued in 1979, and two revisions to the data file were provided in subsequent years, the latest occurring in 1981. A total of 75 new or extensively modified neutron sublibrary evaluations are included in ENDF/B-VI, and are summarized in this document. One incident proton sublibrary is described for Fe{sup 56}. The remaining evaluations in ENDF/B-VI have been carried over from earlier versions of ENDF, and have been updated to reflect the new formats. The release of ENDF/B-VI was carried out between January and June of 1990, with groups of materials being released on tapes.'' Table 1 is an index to the evaluation summaries, and includes the material identification or MAT number, the responsible laboratory, and the tape'' number. These evaluations have been released without restrictions on their distribution or use.
Date: October 1, 1991
Creator: Rose, P.F. (comp.)
Partner: UNT Libraries Government Documents Department

Bubble growth in superheated He-II

Description: Bubble growth in superheated He-II is controlled by the transfer of heat to the surface of the growing bubble by nonlinear Gorter-Mellink counterflow. The present work presents analytic formulas for the bubble radius as a function of time in the limiting cases of small and large superheats. The formulas include the effect of the inertial reaction of the surrounding liquid to the expansion of the bubble. A numerical example shows that bubble velocities of the order of meters per second are possible. A related problem, involving only heat transfer but no movement of the liquid, is the motion of the free surface of superheated He-II in a very long tube. This problem has a similarity solution. The interfacial velocity in the tube is much smaller than the bubble growth velocity. 1 ref.
Date: January 1, 1988
Creator: Dresner, L.
Partner: UNT Libraries Government Documents Department

Equipment and techniques for remote fabrication and calibration of physically small, high intensity /sup 252/Cf neutron sources

Description: Special equipment and techniques were required to fabricate /sup 252/Cf neutron source capsules, in which milligram quantities of /sup 252/Cf were concentrated in each capsule to approximate an idealized ''point source'' as closely as possible. Through this cooperative effort with the National Bureau of Standards all /sup 252/Cf neutron against the national reference radium-beryllium source.
Date: January 1, 1976
Creator: Williams, L. C.; Bigelow, J. E. & Knauer, J. B. Jr.
Partner: UNT Libraries Government Documents Department

Systematics of Alpha-Radioactivity

Description: Correlations of alpha-decay energies in terms of mass number and atomic number have been made for all of the alpha-emitting species now numbering over 100. For each element isotopes show increase in alpha-energy with decrease in mass number except in the region of 126 neutrons where there is an explainable reversal. This reversal has the effect of creating a region of relatively low alpha-energy and long half-life at low mass numbers for such elements as astatine, emanation, francium, and possibly higher elements as had been noted already for bismuth and polonium. Methods and examples of using alpha-decay data to define the energy surface in the heavy element region are discussed. The regularities in alpha-decay are used for predictions of nuclear properties including prediction of the beta-stable nuclides among the heavy elements. The half-life vs. energy correlations show that the even-even nuclides conform well with existing alpha-decay theory, but all nuclear types with odd nucleons show prohibited decay. The reason for this prohibition is not found in spin changes in the alpha-emission but in the assembly of the components of the alpha particle, and this theory is discussed further in terms of observations made on nuclides having two or more alpha-groups. Using most of the even-even nuclei to define 'normal nuclear radius' calculations are now able to show the shrinkage in the regions of lead and of 126 neutrons to amount to about 10%. The much greater change in 'effective radius' for bismuth isotopes can be dissociated into the effects of odd nucleons superimposed on the actual decrease in nuclear radius. The simple expression r = 1.48 A{sup 1/3} {center_dot} 10{sup -13} cm seems to fit the data for the even-even nuclei outside of the region of 126 neutrons better than more complex functions.
Date: September 12, 1949
Creator: Perlman, I.; Ghiorso, A. & Seaborg, G.T.
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

Fermion dynamical symmetry and identical bands

Description: Recent general attention has been directed to the phenomenon of identical bands in both normally deformed and superdeformed nuclei. This paper discusses the possibility that such behavior results from a dynamical symmetry of the nuclear many-body system. Phenomenology and the basic principles of Lie algebras are used to place conditions on the acceptable properties of a candidate symmetry. We find that quite general arguments require that such a symmetry have a minimum of 21 generators with a microscopic fermion interpretation.
Date: October 1, 1994
Creator: Guidry, M.
Partner: UNT Libraries Government Documents Department

Systematics of effective charges of proton and neutron bosons

Description: Experimental B(E2; 0{sub 1}{sup +} {r arrow} 2{sub 1}{sup +}) values for 54 even-even nuclei in the range A = 90--200 were used to deduce effective charges of proton, neutron bosons. The results indicate that for deformed nuclei, the ratio e{sub n}/e{sub p} is in general agreement with the schematic Bohr and Mottelson prediction. For vibrational nuclei in the A = 100 and A = 140 regions a very significant enhancement of this ratio is found. 6 refs., 3 figs.
Date: January 1, 1990
Creator: Wolf, A. (Israel Atomic Energy Commission, Beersheba (Israel). Nuclear Research Center-Negev) & Casten, R.F. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department