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The positron peak puzzle - recent results from APEX

Description: Results are presented from a new experiment, APEX, designed to study the previously reported sharp lines in sum-energy spectra of positrons and electrons produced in collisions of very heavy ions. Data have been collected for {sup 238}U+{sup 181}Ta and {sup 238}U+{sup 232}Th. No evidence is found for narrow structures similar to those previously reported. For the specific case of the isolated decay of a neutral particle of mass 1.4-2.1 MeV/c{sup 2}, the upper limits on cross sections obtained are significantly less than previously reported. Data are also presented for internal pair conversion in {sup 206}Pb. These results are used to set limits for the possible contribution to the pair yield of a 1780 keV transition in {sup 238}U observed in heavy-ion gamma-ray coincidence measurements.
Date: December 31, 1995
Creator: Ahmad, I.; Back, B.B. & Kutschera, W.
Partner: UNT Libraries Government Documents Department

A new look at positron production from heavy-ion collisions: Results from apex

Description: A new solenoidal spectrometer, designed to study the production mechanism of electrons and positrons in heavy-ion collisions, has been constructed at Argonne National Laboratory. The spectrometer has been used to study the {sup 238}U + {sup 181}Ta system at 5.95, 6.10, and 6.30 MeV/u and the {sup 238}U + {sup 232}Th system at 5.95 MeV/u. These bombarding energies cover the energy region where previous experiments have reported sharp sum-energy lines. No evidence is found for sharp peaks in the present data. For the specific case of the isolated decay of a neutral particle of mass 1.4--2.1 MeV/c{sup 2} the upper limits on cross sections obtained from the present data are significantly less than the previously reported cross sections.
Date: December 31, 1995
Creator: Ahmad, I.; Back, B.B. & Austin, S.M.
Partner: UNT Libraries Government Documents Department

Spectroscopy of reflection-asymmetric nuclei using multinucleon transfer reactions

Description: The heavy-ion collisions of {sup 56}Fe + {sup 232}Th, {sup 86}Kr + {sup 232}Th and {sup 136Xe} + {sup 232}Th with beam energies 15--20% above the Coulomb barrier were used to populate nuclei in the light-actinide region. Yield distributions of the binary reaction products stopped in thick targets were obtained by measuring {gamma}-{gamma} coincidence intensities. The {sup 136}Xe + {sup 232}Th reaction was repeated at Lawrence Berkeley National Laboratory using a recent implementation of the GAMMASPHERE array. Many interesting discoveries concerning the high-spin structure of octupole-deformed light-actinide nuclei have been made.
Date: December 1, 1996
Creator: Cocks, J.F.C.; Butler, P.A. & Cann, K.J.
Partner: UNT Libraries Government Documents Department

Neutron scattering from elemental uranium and thorium

Description: Differential neutron-scattering cross sections of elemental uranium and thorium are measured from {approx} 4.5 to 10.0 MeV in steps of {approx} 0.5 MeV. Forty or more differential values are obtained at each incident energy, distributed between {approx} 17{degree} and 160{degree}. Scattered-neutron resolutions are carefully defined to encompass contributions from the first four members of the ground-state rotational band (0{sup 2} g.s., 2{sup +}, 4{sup +} and 6{sup +} states). The experimental results are interpreted in the context of coupled-channels rotational models, and comparisons made with the respective ENDF/B-VI evaluated files. These comparisons suggest some modifications of the ENDF/B-VI {sup 238}U and {sup 232}Th evaluations.
Date: January 1, 1995
Creator: Smith, A.B. & Chiba, S.
Partner: UNT Libraries Government Documents Department

Environmental sampling and analysis as a safeguards tool

Description: Environmental sampling and radionuclide analysis of the resulting material can be utilized as a supplemental approach in safeguarding practices and particularly for detection of undeclared nuclear activities. The production of nuclear weapons could be pursued by uranium enrichment processes to produce highly enriched U-235 or by nuclear reactor operations followed by chemical separations to produce Pu-239. The application of either of these processes results in the production of signature materials, some of which will be released to the environs. Results from the operations of the Hanford production facilities are discussed and indicate the type of signatures that may be expected from plutonium production facilities. These include noble gas emissions from the reactors and chemical separations processes, the production of radionuclides in reactor cooling water followed by their subsequent release to the Columbia River, and the release of mildly contaminated process water from the chemical processing facilities. These signature materials are carried by both gaseous and liqid effluents and enter various compartments of the environment. The types of signature materials which are most likely to be accumulated are discussed, together with examples of the quantities which have been released during past separations. There are numerous processes by which natural uranium may be enriched to produce highly enriched U-235. The most definitive signature of such processes is always a modification in uranium isotope ratios, and materials showing either enriched or depleted uranium in gaseous and liquid effluents provide the best indication that uramium enrichment processes are taking place. Therefore, techniques for sampling and analysis of airborne, waterborne, or deposited uranium in environmental matrices provide a means of detecting uranium enrichment which may lead to proliferation products.
Date: March 1, 1994
Creator: Perkins, R.W.; Wogman, N.A. & Holdren, G.R.
Partner: UNT Libraries Government Documents Department

Cost-based optimizations of power density and target-blanket modularity for {sup 232}Th/{sup 233}U-based ADEP

Description: A cost-based parametric systems model is developed for an Accelerator-Driven Energy Production (ADEP) system based on a {sup 232}Th/{sup 233}U fuel cycle and a molten-salt (LiF/BeF{sub 2}/ThF{sub 3}) fluid-fuel primary system. Simplified neutron-balance, accelerator, reactor-core, chemical-processing, and balance-of-plant models are combined parametrically with a simplified costing model. The main focus of this model is to examine trade offs related to fission power density, reactor-core modularity, {sup 233}U breeding rate, and fission product transmutation capacity.
Date: July 1, 1995
Creator: Krakowski, R.A.
Partner: UNT Libraries Government Documents Department

Detection of Actinides via Nuclear Isomer De-Excitation

Description: This dissertation discusses a data collection experiment within the Actinide Isomer Identification project (AID). The AID project is the investigation of an active interrogation technique that utilizes nuclear isomer production, with the goal of assisting in the interdiction of illicit nuclear materials. In an attempt to find and characterize isomers belonging to 235U and its fission fragments, a 232Th target was bombarded with a monoenergetic 6Li ion beam, operating at 45 MeV.
Date: July 22, 2009
Creator: Francy, Christopher J.
Partner: UNT Libraries Government Documents Department

Evaluated nuclear data file of Th-232

Description: An evaluated nuclear data file for thorium is described. The file extends over the energy range 0.049 (i.e., the inelastic-scattering threshold) to 20.0 MeV and is formulated within the framework of the ENDF system. The input data base, the evaluation procedures and judgments, and ancillary experiments carried out in conjunction with the evaluation are outlined. The file includes: neutron total cross sections, neutron scattering processes, neutron radiative capture cross sections, fission cross sections, (n;2n) and (n;3n) processes, fission properties (e.g., nu-bar and delayed neutron emission) and photon production processes. Regions of uncertainty are pointed out particularly where new measured results would be of value. The file is extended to thermal energies using previously reported resonance evaluations thereby providing a complete file for neutronic calculations. Integral data tests indicated that the file was suitable for neutronic calculations in the MeV range.
Date: September 1, 1977
Creator: Meadows, J.; Poenitz, W.; Smith, A.; Smith, D.; Whalen, J. & Howerton, R.
Partner: UNT Libraries Government Documents Department

Fission channel analysis for /sup 232/Th(n,f)

Description: Angular distributions of fission fragments produced in the /sup 232/Th(n,f) reaction have been measured in 40-keV intervals. A simplified reaction model was adopted, and a channel analysis done for 0.72 less than or equal to E/sub n/ (MeV) less than or equal to 4.5. An anomaly at E/sub n/ = 2.98 MeV suggests that K remains a good quantum number some 2 MeV above fission threshold. The percentage contribution to the cross section of K = 3/2 states for incident neutron energies between 1.1 and 1.3 MeV is larger than previously thought. 7 refs.
Date: May 1, 1985
Creator: Becker, J.A. & Bauer, R.W.
Partner: UNT Libraries Government Documents Department

Fast-neutron capture cross sections of importance in technological applications. [Review]

Description: The importance of the capture cross section of the major fertile nuclei, /sup 238/U and /sup 232/Th, leads to the consideration of these data. The /sup 238/U (n,..gamma..) cross section is considered of priority as it is part of the /sup 238/U-/sup 239/Pu cycle. Experimental techniques used in the measurements of these data are considered. Data measured more recently are compared with provisions made for the possible explanations of differing results. It is concluded that the /sup 238/U (n,..gamma..) cross section is known with approx. 5% above 10 keV and fulfills the uncertainty limit for this cross section set to achieve design accuracy for k/sub eff/ and the breeding ratio above 500 keV. Below 500 keV, the present uncertainty falls short of the required 1.5 to 3.0% uncertainty. Specific recommendations are made to resolve existing discrepancies and data uncertainties. 84 references.
Date: January 1, 1979
Creator: Poenitz, W.P.
Partner: UNT Libraries Government Documents Department

Measurement of the integral capture and fission cross sections for /sup 232/Th in the CFRMF

Description: The recent evaluation of the cross-section data bases for /sup 232/Th capture and fission emphasized significant normalization discrepancies between the available differential data. To help resolve the normalization discrepancies, the capture and fission integral cross sections were measured for /sup 232/Th in the fast neutron zone of the Coupled Fast Reactivity Measurements Facility (CFRMF). The cross sections are derived from the radiometric determination of the saturation reaction rates for fission and capture based on the Ge(Li) spectrometric measurement of the absolute gamma emission rates of the 537-keV and 1596-keV lines in the /sup 140/Ba - /sup 140/La decay and the 311.9-keV line in the /sup 233/Pa decay. For capture and fission, respectively, the measured integral cross sections are 291 mb +- 3% and 19.6 mb +- 5%. The ratios of the integral cross sections computed with ENDF/B-IV thorium cross sections and the CFRMF neutron spectrum to the above values are 0.99 for capture and 0.90 for fission. 19 references.
Date: January 1, 1979
Creator: Anderl, R.A. & Harker, Y.D.
Partner: UNT Libraries Government Documents Department

Neutron induced fission cross section ratios for /sup 232/Th, /sup 235,238/U, /sup 237/Np, and /sup 239/Pu from 1 to 400 MeV

Description: Time-of-flight measurements of neutron induced fission cross section ratios for /sup 232/Th, /sup 235,238/U, /sup 237/Np, and /sup 239/Pu, were performed using the WNR high intensity spallation neutron source located at Los Alamos National Laboratory. A multiple-plate gas ionization chamber located at a 20-m flight path was used to simultaneously measure the fission rate for all samples over the energy range from 1 to 400 MeV. Because the measurements were made with nearly identical neutron fluxes, we were able to cancel many systematic uncertainties present in previous measurements. This allows us to resolve discrepancies among different data sets. In addition, these are the first neutron-induced fission cross section values for most of the nuclei at energies above 30 MeV. 8 refs., 3 figs.
Date: January 1, 1988
Creator: Lisowski, P.W.; Ullmann, J.L.; Balestrini, S.J.; Carlson, A.D.; Wasson, O.A. & Hill, N.W.
Partner: UNT Libraries Government Documents Department

High-resolution photofission measurements in /sup 238/U and /sup 232/Th. Progress report, June 1, 1979-February 10, 1980. [5 to 12 MeV]

Description: High-intensity proton beams have been used to generate gamma rays of well-defined and variable energy from the (p,..gamma..) reaction on a number of targets. Spectra of photofission fragments of /sup 238/U and /sup 232/Th have been measured at gamma ray energies from 5.8 to 11.5 MeV. The photofission cross sections have been determined and preliminary values of barrier parameters, derived by fitting the data to model predictions.
Date: February 1, 1980
Creator: Lancman, H.
Partner: UNT Libraries Government Documents Department

High-resolution photofission measurements in /sup 238/U and /sup 232/Th. Progress report, June 1, 1980-February 10, 1981

Description: Intense proton beam currents from the Dynamitron at Brooklyn College have been used to generate gamma rays of variable energy from a number of (p,..gamma..) resonances in various nuclei. Spectra of photofission fragments of /sup 238/U and /sup 232/Th have been measured with an average gamma ray energy resolution of approx. 300 eV. Structure in the photofission cross section of /sup 232/Th was observed at approx. 6176 keV.
Date: February 1, 1981
Creator: Lancman, H.
Partner: UNT Libraries Government Documents Department

Review and combination of experimental results for neutron emission per fission of /sup 232/Th. [1 to 16 MeV]

Description: An analysis was made of the existing experimental data for ..nu..-bar(E) of /sup 232/Th, the average number of neutrons emitted per fission of /sup 232/Th. This analysis suggests that a single linear function of the neutron energy describes the data within their uncertainties. The parameters of the linear function and their uncertainties are given. 1 figure, 5 tables.
Date: May 1, 1978
Creator: Gwin, R.
Partner: UNT Libraries Government Documents Department

Evaluation of the /sup 232/Th neutron capture cross section above 3 keV

Description: This memo describes an evaluation of the /sup 232/Th neutron capture cross section in the neutron energy range from 3 keV to 20 MeV. Most existing differential measurements are reviewed, and some data are renormalized to current values of the standards. Several experimentally determined sets of average resonance parameters are also discussed. From 3 to 50 keV the evaluated cross section is described by a set of average statistical resonance parameters. Above 50 keV the evaluated capture cross section is a smooth curve which follows the trend of the most recent measurements. The evaluated capture cross section is compared with many measurements and uncertainty estimates are given.
Date: December 1, 1977
Creator: de Saussure, G. & Macklin, R.L.
Partner: UNT Libraries Government Documents Department

Study of proton-induced reactions and correlation with fast-neutron scattering

Description: The generation of cross sections for fast neutron-nucleon interactions obtained from elastic and charge-exchange proton data is discussed in terms of the Lane model formalism. A general description of the interaction of nucleons with nuclei is presented in terms of the optical model and the extended (or coupled-channel) optical model, together with the relation of these models to microscopic calculations of the nucleon-nucleon interaction. Comparisons between neutron elastic data and calculations carried out with optical model potentials obtained from (p,p) and (p,n) data are presented for a large number of nuclei. The validity of the Lane model and the importance of coupled effects in the actinide region are shown in a detailed comparison of calculations for elastic and inelastic neutron differential cross sections and measurements for /sup 232/Th and /sup 238/U.
Date: January 19, 1982
Creator: Hansen, L.F.
Partner: UNT Libraries Government Documents Department

Fission cross sections of some thorium, uranium, neptunium and plutonium isotopes relative to /sup 235/U

Description: Earlier results from the measurements, at this Laboratory, of the fission cross sections of /sup 230/Th, /sup 232/Th, /sup 233/U, /sup 234/U, /sup 236/U, /sup 238/U, /sup 237/Np, /sup 239/Pu, /sup 240/Pu, and /sup 242/Pu relative to /sup 235/U are reviewed with revisions to include changes in data processing procedures, alpha half lives and thermal fission cross sections. Some new data have also been included. The current experimental methods and procedures and the sample assay methods are described in detail and the sources of error are presented in a systematic manner. 38 references.
Date: October 1, 1983
Creator: Meadows, J W
Partner: UNT Libraries Government Documents Department

Fission cross section of /sup 239/Th and /sup 232/Th relative to /sup 235/U. [Threshold to 10 MeV, cross sections]

Description: The fission cross sections of /sup 230/Th and /sup 232/Th were measured relative to /sup 235/U from near threshold to near 10 MeV. The weights of the thorium samples were determined by isotopic dilution. The weight of the uranium deposit was based on specific activity measurements of a /sup 234/U-/sup 235/U mixture and low geometry alpha counting. Corrections were made for thermal background, loss of fragments in the deposits, neutron scattering in the detector assembly, sample geometry, sample composition and the spectrum of the neutron source. Generally the systematic errors were approx. 1%. The combined systematic and statistical errors were typically 1.5%. 17 references.
Date: January 1, 1979
Creator: Meadows, J.W.
Partner: UNT Libraries Government Documents Department

Review of (n; n',. gamma. ) cross-section data on actinide nuclei

Description: The available high-resolution (n;n',..gamma..) cross section data on actinide nuclei, essentially /sup 238/U and /sup 232/Th, are reviewed by dividing the measurement process into two steps. First, the measurement of discrete photon production cross sections is discussed by comparing white and monoenergetic neutron source techniques. Resultant cross sections are compared and their accuracies assessed. Second, the step of inferring inelastic scattering cross sections from photon production cross sections is discussed with particular emphasis on the problems connected with monopole transitions, low-energy transitions, prompt fission photons, and simple rotational models. The uncertainties introduced in this step are probably larger than those of the first.
Date: January 1, 1981
Creator: Olsen, D.K.
Partner: UNT Libraries Government Documents Department

K-components for the approx. 1. 4-, approx. 1. 6-, and approx. 1. 7-MeV structures in the fission of /sup 232/Th + n

Description: Neutron-induced angle-integrated fission cross sections of /sup 232/Th were measured from 0.7 to 9 MeV with a nominal neutron energy resolution of 0.15 ns/m. Data were taken for the angular intervals 0 to 23.4/sup 0/, 0 to 33.7/sup 0/, 0 to 51.7/sup 0/, and 0 to 90/sup 0/. The structures at approx. 1.4, approx. 1.6, and approx. 1.7 MeV were interpreted in terms of rotational bands with K = 1/2, 3/2, and greater than or equal to 5/2. The approximate relative fission strengths for the K-bonds are in the proportion 1.7:2.4:1.0, 0.0:2.6:1.0, and 1.0:2.8:0.0 for the three structures, respectively.
Date: July 1, 1981
Creator: Auchampaugh, G.F.; Plattard, S.; Hill, N.W.; de Saussure, G.; Perez, R.B. & Harvey, J.A.
Partner: UNT Libraries Government Documents Department

Fast neutron radiative capture cross section of /sup 232/Th. [30 keV to 2. 5 MeV]

Description: The /sup 232/Th(n,..gamma..) cross section was measured between 30 keV and 2.5 MeV. A large liquid scintillator was used to measure the shape of the cross section relative to Au(n,..gamma..) between 58 keV and 850 keV. The activation technique was used in measurements at 30 keV relative to Au(n,..gamma..) and above 240 keV relative to /sup 235/U(n,f). The activation results were utilized to normalize the shape data. The results agree well with recent experimental data by Lindner et al. and are substantially lower than the evaluated data file ENDF/B-IV in the several-hundred-keV range.
Date: March 1, 1978
Creator: Poenitz, W.P. & Smith, D.L.
Partner: UNT Libraries Government Documents Department

Covariances for measured activation and fission ratios data

Description: Methods which are routinely used in the determination of covariance matrices for both integral and differential activation and fission-ratios data acquired at the Argonne National Laboratory Fast-Neutron Generator Facility (FNG) are discussed. Special consideration is given to problems associated with the estimation of correlations between various identified sources of experimental error. Approximation methods which are commonly used to reduce the labor involved in this analysis to manageable levels are described. Results from some experiments which have been recently carried out in this laboratory are presented to illustrate these procedures. 13 refs., 1 fig., 5 tabs.
Date: January 1, 1986
Creator: Smith, D.L.; Meadows, J.W. & Watanabe, Y.
Partner: UNT Libraries Government Documents Department