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Calibration and performance testing of the IAEA Aquila Active Well Coincidence Counter (Unit 1)

Description: An Active Well Coincidence Counter (AWCC) and a portable shift register (PSR-B) produced by Aquila Technologies Group, Inc., have been tested and cross-calibrated with existing AWCCs used by the International Atomic Energy Agency (IAEA). This report summarizes the results of these tests and the cross-calibration of the detector. In addition, updated tables summarizing the cross-calibration of existing AWCCs and AmLi sources are also included. Using the Aquila PSR-B with existing IAEA software requires secondary software also supplied by Aquila to set up the PSR-B with the appropriate measurement parameters.
Date: January 1, 1996
Creator: Menlove, H.O..; Siebelist, R. & Wenz, T.R.
Partner: UNT Libraries Government Documents Department

Chemical identity of atoms using core electron annihilations

Description: Positron annihilation spectroscopy is a sensitive probe for studying the electronic structure of defects in solids. The high momentum part of the Doppler-broadened annihilation spectra can be used to distinguish different elements. This is achieved by using a new two-detector coincidence system and by imposing appropriate kinematic cuts to exclude background events. The new setup improves the peak to background ratio in the annihilation spectrum to {approximately}10{sup 5}. As a result, the line shape variations arising from different core electrons can be studied. The new approach adds elemental specificity to the Doppler broadening technique, and is useful in studying elemental variations around a defect site. Results from several case studies are reviewed.
Date: June 27, 1997
Creator: Asoka-Kumar, P.
Partner: UNT Libraries Government Documents Department

MEGA -- A search for {mu} {r_arrow} e{gamma}

Description: The MEGA experiment is a search for the decay {mu} {r_arrow} e{gamma}. Even though there is no fundamental reason to expect lepton number to be a conserved quantity, processes such as {mu} {r_arrow} e{gamma} have not been observed. (The present upper limit for the branching ratio for {mu} {r_arrow} e{gamma} is 4.9 x 10{sup {minus}11}.) The minimal standard model of electroweak interactions, which is enormously successful, builds in lepton number conservation. However, the decay {mu} {r_arrow} e{gamma} is expected in many extensions to the standard model, in particular in supersymmetry models. The experimental signature for {mu} {r_arrow} e{gamma} from decays at rest is the observation of a positron and photon, each of 52.8 MeV , that are back-to-back, in time coincidence, and originate from a common spatial point. The MEGA detector consists of two spectrometers designed to measure the kinematic characteristics of positrons and photons to search for events with this signature. The primary difficulty in the analysis of these data has been the development of reconstruction algorithms that balance efficiency and resolution. Also, many calibrations and corrections are needed to get optimum resolutions. Most surviving candidate events are accidentals. Results of analysis are given.
Date: December 1, 1998
Creator: Mischke, R. E.
Partner: UNT Libraries Government Documents Department


Description: A hybrid approach was adopted in the use of an on-line computer in setting up and analyzing nuclear physics experiments. In addition to the usually cited advantage of online flexibility and the ability to do off-line calculations, the general purpose computer can simulate data by preserting the results of off-line calculations to the experimenter in a format identical to that used for data display. As compared with off-line calculations at a computer center with subsequent hand or machine plotting, the use of the build-in display hardware provides a more convenient comparison of theory with experiment, as well as greater ease and speed. The advantages of on-line data transformation are preserved without accompanying limitations on the rate of data taking. The data from the experiment consisted of energy correlations in two-particle coincidence experiments. The loci of points in energy-energy space fulfilling energy and momentum conservation were calculated, displayed, and photographed before each experimental run. Interpretation of the experimertal data was assisted by modulation of the loci (of the number of counts per channel) according to the predictions of various models. (auth)
Date: February 19, 1964
Creator: Mollenauer, J.F.
Partner: UNT Libraries Government Documents Department

Deadtime effects in coincidence counting: A new model. Revised

Description: This paper described a model for correcting deadtime effects in coincidence counting. The correction is based on waiting time distribution for the detection of particles. The waiting time distribution is expressed as integrals of correlation functions, using Sratonivich`s theory of random set of points. The correlation functions are solved from the basic equation governing the probability.
Date: April 1, 1997
Creator: Lu, Ming-Shih & Teichmann, T.
Partner: UNT Libraries Government Documents Department

Non-destructive measurement technologies for nuclear safeguards

Description: There are three aspects that need to be in place in order to maintain a valid safeguards system: (1) Physical protection; guarding the access to nuclear materials using physical protection and surveillance. (2) Accounting systems; computer based accounting systems that provide the current location of nuclear materials, quantities, and the uncertainty in the assayed values. (3) Measurement systems; detectors, data acquisition systems and data analysis methods that provide accurate assays of nuclear material quantities for the accounting system. The authors expand on this third aspect, measurement systems, by discussing nondestructive assay (NDA) techniques. NDA is defined as the quantitative or qualitative determination of the kind and/or amount of nuclear material in an item without alteration or invasion of the item. This is contrasted with destructive analysis which is the process of taking small samples from the item in question, analyzing those samples by chemical analysis, destroying the original nature of the samples in the process (hence the term destructive), and applying the results to the entire item. Over the past 30 years, numerous techniques, using the atomic and nuclear properties of the actinides, have been developed for reliable, rapid, accurate, and tamper-proof NDA of nuclear materials. The authors distinguish between two types of measurements: the first involving the detection of spontaneously emitted radiation, produced by the natural radioactive decay processes; the second involving the detection of induced radiation, produced by irradiating the sample with an external radiation source.
Date: April 1, 1998
Creator: Gavron, A.
Partner: UNT Libraries Government Documents Department

Non-destructive analysis of impure HEU-carbon samples using an Active Well Coincidence Counter (AWCC)

Description: Highly enriched uranium-containing graphite-based material from the Los Alamos National Laboratory (LANL) is currently stored at the Idaho National Engineering and Environmental Laboratory (INEEL). Measurements to verify the uranium content of these samples are required prior to their disposition to the Y-12 facility in Tennessee. The stored materials vary significantly in their matrix purity and in their {sup 235}U content and enrichment. A set of 26 samples selected from the LANL material inventory were analyzed non-destructively using an Active Well Coincidence Counter (AWCC) calibrated versus pure UO{sub 3} standards. A correction, calculated from published data and the approximate carbon-to-uranium atom ratios of each sample, was applied for the response enhancement from the carbon matrix. In some cases this correction was as high as 30%. Eight of the 26 sample that had been analyzed in the AWCC were destructively analyzed to provide a benchmark for the non-destructive analyses. The average recovery (NDA/Destructive results) was 0.997 {+-} 0.115. One sample had a destructive result that lay outside a 3-sigma interval about the NDA result.
Date: July 1, 1998
Creator: Hartwell, J.K. & McLaughlin, G.D.
Partner: UNT Libraries Government Documents Department

Energy dependent bias in plutonium verification measurements using thermal neutron multiplicity counters

Description: Multiplicity analysis algorithms are extended to include the effect of ({alpha}, n) neutron energies on the detector efficiencies, induced fission probabilities, and induced fission factorial moments. The analysis is restricted to plutonium oxide. Bias is calculated as a function of ({alpha}, n) neutron energy for six thermal neutron coincidence counters: HLNC, AWCC, 3RMC, PSMC, PYRO, and 5RMC. Ring ratio data for the 3RMC are used to reduce energy dependent bias in the verification of impure plutonium oxide. The utility of the AWCC as a multiplicity counter is considered.
Date: October 1, 1997
Creator: Krick, M.S.; Langner, D.G. & Stewart, J.E.
Partner: UNT Libraries Government Documents Department


Description: Active well coincidence counter assays have been performed on uranium metal highly enriched in {sup 235}U. The data obtained in the present program, together with highly enriched uranium (HEU) metal data obtained in other programs, have been analyzed using two approaches, the standard approach and an alternative approach developed at BNL. Analysis of the data with the standard approach revealed that the form of the relationship between the measured reals and the {sup 235}U mass varied, being sometimes linear and sometimes a second-order polynomial. In contrast, application of the BNL algorithm, which takes into consideration the totals, consistently yielded linear relationships between the totals-corrected reals and the {sup 235}U mass. The constants in these linear relationships varied with geometric configuration and level of enrichment. This indicates that, when the BNL algorithm is used, calibration curves can be established with fewer data points and with more certainty than if a standard algorithm is used. However, this potential advantage has only been established for assays of HEU metal. In addition, the method is sensitive to the stability of natural background in the measurement facility.
Date: July 19, 2000
Partner: UNT Libraries Government Documents Department

Time-Dependent Coincidence Method to Measure Plutonium Mass and Multiplication

Description: Future nuclear disarmament agreements between nations may require technical measures to ascertain each participating nation's adherence to the agreement. Almost certainly, measurement technologies and analytical methods will have to be developed by the participating nations jointly. In this way each participant has both confidence in the technology's efficacy and trust in its implementation. With the support of the National Nuclear Security Administration's Office of Nonproliferation Policy (NNSA NA-241), the Oak Ridge National Laboratory (ORNL) and the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) have taken first steps to jointly develop and implement a radiation measurement technique to inspect plutonium. In June and July 2000, personnel from ORNL and VNIIEF performed joint experiments on unclassified plutonium metal ({delta}-phase, 1.77%-{sup 240}Pu) spherical shells at VNIIEF facilities in Sarov, Russia [1,2]. The measurements were performed using the Nuclear Materials Identification System (NMIS). The subsequent analysis demonstrates how NMIS can be applied to passively measure the mass and multiplication of plutonium spherical shells.
Date: December 17, 2001
Creator: Mattingly, J. K.; Neal, J. S. & Mihalczo, J. T.
Partner: UNT Libraries Government Documents Department


Description: The analysis of gamma-ray spectra measured with a scintillation counter with an anticoincidence annulus is described in detail. In particular the problem of the determination of the energy and intensity of gamma rays from such measurements is considered. The shapes of the full-energy peaks in observed complex spectra are studied and an attempt is made to justify their description in terms of a Gaussian response function. The details of the statistical analysis of complex gamma-ray spectra are given and, finally, procedures which have been used to confirm the validity of error estimates in energy and intensity measurements are described. (auth)
Date: April 1, 1962
Creator: Julke, R.T.; Monahan, J.E.; Raboy, S. & Trail, C.C.
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

Probing excited states in nuclei at and beyond the proton dripline.

Description: The coupling of a Compton-suppressed Ge (CSGe) detector array to a recoil separator has seen limited use in the past due to the low efficiency for measuring recoil--{gamma} ray coincidences (< 0.1%). With the building of new generation recoil separators and gamma-ray arrays, a substantial increase in detection efficiency has been achieved. This allows for the opportunity to measure excited states in nuclei with cross-sections below 100 nb. In this paper, results from the coupling of a modest array of CSGe detectors (AYE-Ball) and a current generation Ge array (Gammasphere) with a recoil separator (FMA) will be presented.
Date: March 15, 1999
Creator: Carpenter, M. P.
Partner: UNT Libraries Government Documents Department

Design and calibration of the AWCC for measuring uranium hexafluoride

Description: An Active Well Coincidence Counter (AWCC) has been modified to measure variable enrichment uranium hexafluoride (UF{sub 6}) in storage bottles. An active assay technique was used to measure the {sup 235}U content because of the small quantity (nominal loading of 2 kg UF{sub 6}) and nonuniform distribution of UF{sub 6} in the storage bottles. A new insert was designed for the AWCC composed of graphite containing four americium-lithium sources. Monte Carlo calculations were used to design the insert and to calibrate the detector. Benchmark measurements and calculations were performed using uranium oxide resulted in assay values that agreed within 2 to 3% of destructive assay values. In addition to UF{sub 6}, the detector was also calibrated for HEU ingots, billets, and alloy scrap using the standard Mode 1 end-plug configuration.
Date: August 1, 1995
Creator: Wenz, T.R.; Menlove, H.O.; WSalton, G. & Baca, J.
Partner: UNT Libraries Government Documents Department


Description: To aid in orientation of a hodoscope system using a rectangular magnet with a uniform field, projections of the trajectory of particles in the horizontal and ventical planes are calculated approximately. Fringing field effects are represented by adding a correction to the length of the magnet and assuming the field to be uniform over the total effective length. The assumption that the source lies in the median plane of the magnet is also used in treating the vertical motion. (D.C.W.)
Date: February 1, 1963
Creator: Sternheimer, R.M.
Partner: UNT Libraries Government Documents Department