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Recent developments in nuclear reaction theories and calculations

Description: A brief review is given of some recent developments in the fields of optical model potentials; level densities; and statistical model, precompound, and direct reaction codes and calculations. Significant developments have occurred in all of these fields since the 1977 Conference on Neutron Cross Sections, which will greatly enhance the ability to calculate high-energy neutron-induced reaction cross sections in the next few years. 11 figures, 3 tables.
Date: May 5, 1980
Creator: Gardner, D. G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Current status of fast-neutron-capture calculations

Description: This work is primarily concerned with the calculation of neutron capture cross sections and capture gamma-ray spectra, in the framework of the Hauser-Feshbach statistical model and for neutrons from the resonance region up to several MeV. An argument is made that, for applied purposes such as constructing evaluated cross-section libraries, nonstatistical capture mechanisms may be completely neglected at low energies and adequately approximated at high energies in a simple way. The use of gamma-… more
Date: April 15, 1982
Creator: Gardner, D. G.
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Partner: UNT Libraries Government Documents Department
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Statistical vs valence neutron neutron capture in /sup 98/Mo

Description: It has often been reported that, in mass regions corresponding to peaks in the neutron strength function, nonstatistical mechanisms contribute a significant or even major portion of the average radiation width in the beginning of the resonance region. This could severely limit the possibility of calculating caputure cross sections for targets where experimental data are lacking, because such direct effects are sensitive to the detailed nuclear level structure in the daughter nucleus. The reacti… more
Date: June 19, 1981
Creator: Gardner, D. G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Difficulties with inferring neutron cross sections from charged-particle reactions

Description: We have investigated problems associated with inferring cross sections for neutron reactions on unstable nuclei in the mass-90 region from charged-particle reactions on nearby stable targets. We conclude that effects due to precompound evaporation, isospin, and multiple reaction paths severely limit the circumstances under which charged-particle studies may be directly and easily converted to neutron cross sections of useful accuracy. 4 refs., 2 figs.
Date: May 7, 1985
Creator: Gardner, D. G. & Gardner, M. A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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New parameterization of the E1 gamma-ray strength function

Description: The giant dipole (GD) parameters of peak energy, width, and cross section were satisfactorily correlated for elements from V to Bi, assuming two overlapping peaks with a separation dependent on deformation. The energy dependence of the GD resonance is assumed to have a Breit-Wigner form, but with an energy-dependent width. The resulting gamma-ray strength function model is used to predict neutron capture cross sections and gamma-ray spectra for isotopes of Ta, Os, and Au. 23 references.
Date: October 18, 1979
Creator: Gardner, D. G. & Dietrich, F. S.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Capture cross section and gamma-ray spectrum calculations for medium-weight nuclei. [Double-peak, energy-dependent Breit-Wigner model]

Description: A double-peak, energy-dependent Breit-Wigner model of the E1 gamma-ray strength function was applied to nuclei from As to Rh, to predict their neutron capture cross sections and capture gamma-ray spectra. A consistent set of model parameters was obtained in this mass region to describe the step in the low-energy tail of the E1 strength function. This step allows agreement with photonuclear data at high energies, the correct GAMMA/sub gamma/ to be obtained for agreement with neutron capture cros… more
Date: November 14, 1979
Creator: Gardner, M. A. & Gardner, D. G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Importance of level structure in nuclear reaction cross-section calculations. Revision 1

Description: It is shown that level-density expressions cannot adequately represent or substitute for level structure information when making calculations of the Hauser-Feshbach type for cross sections or isomer-ratios for nuclei in the first few MeV above their ground state. It is stated that such discrete level information should include both experimentally confirmed and theoretically predicted levels. The utility of discrete level information to optimize level density calculations, to compute isomer rati… more
Date: November 7, 1985
Creator: Gardner, M. A. & Gardner, D. G.
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Partner: UNT Libraries Government Documents Department
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Preliminary evaluation of neutron capture cross sections for /sup 144/Sm, /sup 145/Sm and /sup 145/Pm

Description: We have made preliminary neutron-capture cross-section calculations of the Hauser-Feshbach type for the isotopes /sup 144/Sm, /sup 145/Sm, and /sup 145/Pm to investigate the production of radioactive /sup 145/Pm by neutron capture on the stable isotope /sup 144/Sm. The calculations were made for incident neutron energies from 2.5 MeV to about 1/sup -4/ or 10/sup -5/ MeV, wherever the first unbound resonance was estimated to occur in each case. At that energy, the calculated value was reduced by… more
Date: February 13, 1986
Creator: Gardner, D. G. & Gardner, M. A.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Calculated neutron capture cross sections for the ground states and isomers of /sup 93/ /sup 94/ and /sup 95/Nb. [Resolved resonance region to 4 MeV, strength functions, statistical model]

Description: Neutron-induced capture cross sections for the ground states and first isomeric states of /sup 93/Nb, /sup 94/Nb and /sup 95/Nb were studied from the resolved resonance region to 4 MeV via statistical model calculations. The production of isomers was included. Inelastic scattering cross sections and gamma-ray production spectra were also calculated. The anti GAMMA/ sub ..gamma..//D ratios were derived from gamma-ray strength function systematics. Total capture cross sections on the ground state… more
Date: September 1, 1978
Creator: Gardner, M. A. & Gardner, D. G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Continued study of the parameterization of the El gamma-ray strength function

Description: The parameterization of the magnitude and the energy dependence of the E1 gamma-ray strength function for the calculation of neutron- and proton-induced capture cross sections and capture gamma-ray spectra is investigated. The energy-dependent Breit-Wigner (EDBW) is reparameterized incorporating a more general expression for the Breit-Wigner line shape. Evaluation of the reparameterized E1 gamma-ray strength function is discussed. (WHK)
Date: June 19, 1981
Creator: Gardner, M. A. & Gardner, D. G.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Downhole pulse tube refrigerators

Description: This report summarizes a preliminary design study to explore the plausibility of using pulse tube refrigeration to cool instruments in a hot down-hole environment. The original motivation was to maintain Dave Reagor`s high-temperature superconducting electronics at 75 K, but the study has evolved to include three target design criteria: cooling at 30 C in a 300 C environment, cooling at 75 K in a 50 C environment, cooling at both 75 K and 30 C in a 250 C environment. These specific temperatures… more
Date: December 1, 1997
Creator: Swift, G. & Gardner, D.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Reaction cross-section calculations using new experimental and theoretical level structure data for deformed nuclei

Description: A technique for modeling level structures of odd-odd nuclei has been used to construct sets of discrete states with energies in the range 0 to 1.5 MeV for several nuclei in the rare-earth and actinide regions. The accuracy of the modeling technique was determined by comparison with experimental data. Examination was made of what effect the use of these new, more complete sets of discrete states has on the calculation of level densities, total reaction cross sections, and isomer ratios. 9 refs.
Date: May 1, 1985
Creator: Hoff, R. W.; Gardner, D. G. & Gardner, M. A.
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Partner: UNT Libraries Government Documents Department
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Detailed photonuclear cross-section calculations and astrophysical applications

Description: We have investigated the role of an isomeric state and its coupling to the ground state (g.s.) via photons and neutron inelastic scattering in a stellar environment by making detailed photonuclear and neutron cross-section calculations for /sup 176/Lu and /sup 210/Bi. In the case of /sup 176/Lu, the g.s. would function as an excellent galactic slow- (s-) process chronometer were it not for the 3.7-h isomer at 123 keV. Our calculations predicted much larger photon cross sections for production o… more
Date: June 15, 1989
Creator: Gardner, D. G.; Gardner, M. A. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Dipole strength functions in the actinide mass region

Description: We have calculated a number of neutron- and photon-induced reactions for the actinide nuclei /sup 232/Th, /sup 238/U, and /sup 237/Np. By fitting average resonance capture (ARC) measurements and total neutron capture data, we deduced absolute dipole strength functions for /sup 233/Th and /sup 239/U. We have found that the M1/E1 ratio is the same as in the /sup 176/Lu case, but the total transition strength was larger by about 27%. 17 refs., 4 figs., 1 tab.
Date: July 15, 1987
Creator: Gardner, D. G.; Gardner, M. A. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Isomer ratio calculations using modeled discrete levels

Description: Isomer ratio calculations were made for the reactions: /sup 175/Lu(n,..gamma..)/sup 176m,g/Lu, /sup 175/Lu(n,2n)/sup 174m,g/Lu, /sup 237/Np(n,2n)/sup 236m,g/Np, /sup 241/Am(n,..gamma..)/sup 242m,g/Am, and /sup 243/Am(n,..gamma..)/sup 244m,g/Am using modeled level structures in the deformed, odd-odd product nuclei. The hundreds of discrete levels and their gamma-ray branching ratios provided by the modeling are necessary to achieve agreement with experiment. Many rotational bands must be include… more
Date: October 16, 1984
Creator: Gardner, M. A.; Gardner, D. G. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Absolute dipole gamma-ray strength functions for /sup 176/Lu

Description: We have derived absolute dipole strength-function information for /sup 176/Lu from an average resonance capture study of /sup 175/Lu with 2-keV neutrons, and from neutron capture cross-section measurements with neutrons from 30 keV to about 1 MeV. We found that we needed to increase our previous estimate of the relative M1/E1 strengths near 5 MeV by a factor of 3, and to revise downward the absolute magnitude of our E1 strength function. We accomplished the latter, while still maintaining conti… more
Date: August 29, 1984
Creator: Gardner, D. G.; Gardner, M. A. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Absolute dipole gamma-ray strength functions for /sup 176/Lu. Supplement

Description: We have derived absolute dipole strength-function information for /sup 176/Lu from an average resonance capture study of /sup 175/Lu with 2-keV neutrons and from neutron capture cross-section measurements with neutrons from 30 keV to about 1 MeV. We found that we needed to increase our previous estimate of the relative M1/E1 strengths near 5 MeV by a factor of 3 and to revise downward the absolute magnitude of our E1 strength function. We accomplished the latter, while still maintaining continu… more
Date: October 16, 1984
Creator: Gardner, D. G.; Gardner, M. A. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Isomer ratio calculations using modeled discrete levels

Description: We have calculated isomer ratios for the /sup 175/Lu(n,..gamma..), /sup 175/Lu(n,2n), /sup 237/Np(n,2n), /sup 241/Am(n,..gamma..), and /sup 243/Am(n,..gamma..) reactions using modeled level structures in the deformed, odd-odd product nuclei. We find: that the hundreds of discrete levels and their gamma-ray branching ratios provided by the modeling are necessary to achieve agreement with experiment, that many rotational bands must be included in order to obtain a sufficiently representative sele… more
Date: August 29, 1984
Creator: Gardner, M. A.; Gardner, D. G. & Hoff, R. W.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Reaction cross-section calculations using new experimental and theoretical level structure data for deformed nuclei

Description: A technique for modeling quasiparticle excitation energies and rotational parameters in odd-odd deformed nuclei has been used to construct sets of discrete states with energy 0 to 1.5 MeV in /sup 176/Lu and /sup 236/Np. These data were used as part of the input for calculation of isomer production cross-section ratios in the /sup 175/Lu(n,..gamma..)/sup 176/Lu and /sup 237/Np(n,2n)/sup 236/Np reactions. In order to achieve agreement with experiment, it has been found necessary to include in the… more
Date: October 5, 1984
Creator: Hoff, R. W.; Gardner, D. G. & Gardner, M. A.
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Partner: UNT Libraries Government Documents Department
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Status report to ERDA Nuclear Data Committee

Description: This status report to the Nuclear Data Committee from LLL summarizes work in the areas of standards, nuclear data applications, nuclear data for safeguards, and nuclear data compilation. A few of these papers, though brief, do contain data. 9 figures, 2 tables. (RWR)
Date: February 11, 1977
Creator: Anderson, J. D.; Browne, J. C. & Gardner, D. G.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Study of gamma-ray strength functions

Description: The use of gamma-ray strength function systematics to calculate neutron capture cross sections and capture gamma-ray spectra is discussed. The ratio of the average capture width, GAMMA/sub ..gamma../-bar, to the average level spacing, D/sub obs/, both at the neutron separation energy, can be derived from such systematics with much less uncertainty than from separate systematics for values of GAMMA/sub ..gamma../-bar and D/sub obs/. In particular, the E1 gamma-ray strength function is defined in… more
Date: August 7, 1980
Creator: Gardner, D. G.; Gardner, M. A. & Dietrich, F. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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