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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

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

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 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

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

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

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

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

The distribution of nuclear quantum states in cold'' rotating nuclei

Description: A statistical analysis of the distribution of level spacings for states with the same spin and parity is described in which the average spacing is calculated for the total ensemble. The resulting distribution of level spacings for states of deformed nuclei with A = 155--185 and Z = 62--77 is the closest to that of a Poisson distribution yet obtained for nuclear levels. However, when only the even-spin, positive-parity data for even-even nuclei are considered, the level-spacing distribution becomes double peaked. The anomalously-large separations are shown to be the result of the low energy of the strongly-correlated, completely-paired yrast configuration of even-even nuclei. Average values of the level spacings also are discussed as a function of spin, parity, and nuclear type (even-even, even-Z- odd-N, etc.). Likewise, deviations from a Poisson distribution for several spacings (s) less than about 60 keV are compared with similar values for {sup 116}Sn on an absolute scale. Such discrepancies are attributed to interactions (level repulsions) which become increasingly significant for s {le} 60 keV. 18 refs., 10 figs.
Date: January 1, 1991
Creator: Garrett, J.D.; German, J.R. (Oak Ridge National Lab., TN (United States)); Courtney, L. (Tennessee Univ., Knoxville, TN (United States). Dept. of Physics and Astronomy) & Espino, J.M. (Seville Univ. (Spain))
Partner: UNT Libraries Government Documents Department

Low-lying collective quadrupole strengths in even-even nuclei

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 quadrupole deformations of even-even nuclei. The energy-weighted sum of the low-lying E2 strengths is found to be remarkably regular in its overall behavior. 17 refs., 2 figs.
Date: January 1, 1990
Creator: Raman, S.
Partner: UNT Libraries Government Documents Department

Final state effects in neutron scattering experiments on momentum distributions in quantum fluids

Description: Using a ''hard core perturbation theory,'' the final state corrections to the impulse approximation are derived for high Q neutron scattering experiments to determine momentum distributions in quantum fluids. The final state broadening depends on the radial distribution function, g(r), and the He-He phase shifts. It has a zero second moment and no Lorentzian wings, satisfying the kinetic energy sum rule. Explicit results are presented for superfluid /sup 4/He.
Date: January 1, 1987
Creator: Silver, R.N.
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

Global set of quadrupole deformation parameters for even-even nuclei

Description: A compilation of experimental results has been completed for the reduced electric quadrupole transition probability (B(E2)up arrow) between the 0/sup +/ ground state and the first 2/sup +/ state in even-even nuclei. This compilation together with certain simple relationships noted by other authors can be used to make reasonable predictions of unmeasured B(E2)up arrow values. The quadrupole deformation parameter ..beta../sub 2/ immediately follows, because ..beta../sub 2/ is proportional to (B(E2)up arrow)/sup 1/2/. 8 refs., 7 figs.
Date: January 1, 1986
Creator: Raman, S. & Nestor, C. W. Jr.
Partner: UNT Libraries Government Documents Department

Photo-induced cataphoretic isotope separation. Progress report, June 15, 1978--June 15, 1979

Description: The studies on radiation-induced cataphoretic isotope separation has been associated with the use of a He:Ne laser as the radiation source in an attempt to obtain separation of /sup 20/Ne and /sup 22/Ne isotopes. A cataphoretic discharge tube containing mixed neon isotopes is within the laser resonator, whereas the laser tube contains only one neon isotope. Cataphoretic separation of the neon isotopes has not been observed, although selective excitation of one isotope has been demonstrated and a very sensitive technique for detecting cataphoretic isotope separation has been developed. Also, it is found that the exchange rate between the two neon isotopes in the excited laser levels is not great enough to significantly reduce the effect of selective excitation. Measurements of the current changes induced by the radiation indicate that the populations of those levels with which the laser radiation interacts is too small.
Date: June 1, 1979
Creator: Carruthers, J.A.
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

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
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