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An integrating image detector for high energy neutrons

Description: We describe an integrating cathode-pad read-out wire chamber for imaging high energy neutrons. This technology allows construction of a detector with a wide dynamic range (10{sup 4}), which is gatable, easily read out, and provides millimeter scale resolution. Results from a prototype 48 x 48 pixel array are presented.
Date: September 1, 1996
Creator: Morris, C.; Armijo, V.; Atencio, L.G. & Bridge, A.
Partner: UNT Libraries Government Documents Department

Instrument design program progress. Final report, May 1 1995--September 30, 1995

Description: The goals of the task for this time period were met, and the resulting tools were used to obtain significant results in a number additional studies. Six presentations will be published in the Proceedings of ICANS-XIII, the 13th Meeting of the International Collaboration on Advanced Neutron Sources, Paul Scherrer Institut, Villigen, Switzerland, October 11-14, 1995. The principle task in this time period and presented here was to make the neutron optics Monte Carlo library MCLIB as general as possible, and to collaborate in the construction of an object-oriented user interface to make it easy for relatively untrained users to use the codes to test neutron instrument designs. As of September 30, the interface could be used to define all element types necessary to study small-angle diffractometers or surface reflectometers.
Date: August 1, 1996
Creator: Seeger, P. A.
Partner: UNT Libraries Government Documents Department

A New Neutron Multiplicity Counter for the Measurement of Impure Plutonium Metal at Westinghouse Savannah River Site

Description: A new neutron multiplicity counter has been designed, fabricated, characterized, and installed for use in the assay of impure plutonium metal buttons from the FB-Line at the Westinghouse Savannah River Site (WSRS). This instrument incorporates the performance characteristics of the Pyrochemical or In-plant Multiplicity Counter with the package size of the Plutonium Scrap Multiplicity Counter. In addition, state-of-the art features such as the de-randomizer circuit and separate ring outputs have been added. The counter consists of 113, 71 cm active length 3He tubes in a polyethylene moderator. Its efficiency for 252Cf is 57.8 percent, the highest of any multiplicity counter to date. Its die-away time is 50.4 ms and its deadtime is 50 ns. In this paper we will present the characterization data for the counter and the results of preliminary metal measurements at WSRS. We will also discuss the new challenges the impure metal buttons from FB-Line are presenting to the multiplicity counting technique.
Date: July 1, 1998
Creator: Baker, L.B.; Faison, D.M.; Langner, D.G.; Sweet, M.R.; Salazar, S.D. & Kroncke, K.E.
Partner: UNT Libraries Government Documents Department

Absolute calibration of TFTR neutron detectors for D-T plasma operation

Description: The two most sensitive TFTR fission-chamber detectors were absolutely calibrated in situ by a D-T neutron generator ({approximately}5 {times} 10{sup 7} n/s) rotated once around the torus in each direction, with data taken at about 45 positions. The combined uncertainty for determining fusion neutron rates, including the uncertainty in the total neutron generator output ({plus_minus}9%), counting statistics, the effect of coil coolant, detector stability, cross-calibration to the current mode or log Campbell mode and to other fission chambers, and plasma position variation, is about {plus_minus}13%. The NE-451 (ZnS) scintillators and {sup 4}He proportional counters that view the plasma in up to 10 collimated sightlines were calibrated by scanning. the neutron generator radially and toroidally in the horizontal midplane across the flight tubes of 7 cm diameter. Spatial integration of the detector responses using the calibrated signal per unit chord-integrated neutron emission gives the global neutron source strength with an overall uncertainty of {plus_minus}14% for the scintillators and {plus_minus}15% for the {sup 4}He counters.
Date: March 1, 1995
Creator: Jassby, D.L.; Johnson, L.C.; Roquemore, A.L.; Strachan, J.D.; Johnson, D.W.; Medley, S.S. et al.
Partner: UNT Libraries Government Documents Department

Summary report on four Oak Ridge sensors for enhancing nuclear safeguards neutron detectors

Description: The need for monitoring weapons grade Pu in nuclear facilities worldwide was addressed with four radiation detector technologies being developed at Y-12 and ORNL. This paper describes experimental results of 4 Oak Ridge Sensors for Enhancing Nuclear Safeguards (ORSENS) neutron detector technologies and includes the potential application, cost, and advantages for each. These are a {sup 6}LiF- ZnS(Ag) thermal neutron scintillator coupled to a wavelength-shifting optical fiber, a CdWO{sub 4} based scintillating thermal neutron detector, a rhodium silicon thermal neutron detector, and a proton- recoil fast neutron detector.
Date: August 1, 1997
Creator: Williams, J.A.; Clark, R.L.; Hutchinson, D.P.; Miller, V.C.; Ramsey, J.A.; Bell, Z.W. et al.
Partner: UNT Libraries Government Documents Department

Prospect for Measuring G{sup n}{sub E} at High Momentum Transfers

Description: Experiment E02-013, approved by PAC21, will measure the neutron electric form factor at Q{sup 2} up to 3.4 (GeV/c){sup 2}, which is twice that achieved to date. The main features of the new experiment will be the use of the electron spectrometer BigBite, a large array of neutron detectors, and a polarized {sup 3}[vec]He target. We present the parameters and optimization of the experimental setup. A concept of an experiment for G{sup n}{sub E} where precision G{sup p}{sub E} data is used for calibration of the systematics of a Rosenbluth type measurement is also discussed.
Date: May 1, 2002
Creator: Wojtsekhowski, Bogdan
Partner: UNT Libraries Government Documents Department

Development of Novel Semi-conducting Ortho-carborane Based Polymer Films: Enhanced Electronic and Chemical Properties

Description: A novel class of semi-conducting ortho-carborane (B10C2H12) based polymer films with enhanced electronic and chemical properties has been developed. The novel films are formed from electron-beam cross-linking of condensed B10C2H12 and B10C2H12 co-condensed with aromatic linking units (Y) (Y=1,4-diaminobenzene (DAB), benzene (BNZ) and pyridine (PY)) at 110 K. The bonding and electronic properties of the novel films were investigated using X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS) and Mulliken charge analysis using density functional theory (DFT). These films exhibit site-specific cross-linking with bonding, in the pure B10C2HX films, occurring at B sites non-adjacent to C in the B10C2H12 icosahedra. The B10C2H12:Y films exhibit the same phenomena, with cross-linking that creates bonds primarily between B sites non-adjacent to C in the B10C2H12 icosahedra to C sites in the Y linking units. These novel B10C2HX: Y linked films exhibit significantly different electron structure when compared to pure B10C2HX films as seen in the UPS spectra. The valence band maxima (VBM) shift from - 4.3 eV below the Fermi level for pure B10C2HX to -2.6, -2.2, and -1.7 for B10C2HX:BNZ, B10C2HX:PY, and B10C2HX:DAB, respectively. The top of the valence band is composed of states derived primarily from the Y linking units, suggesting that the bottom of the conduction band is composed of states primarily from B10C2H12. Consequently these B10C2HX:Y films may exhibit longer electron-hole separation lifetimes as compared to pure B10C2HX films. This research should lead to an enhancement of boron carbide based neutron detectors, and is of potential significance for microelectronics, spintronics and photo-catalysis.
Date: August 2013
Creator: Pasquale, Frank L.
Partner: UNT Libraries

Physics group progress report, July 1--31, 1948

Description: Preparatory work is described for the determination of the vapor pressure of postum (Polonium 210), selenium being used as a surrogate in construction and testing of the apparatus to measure vapor pressure. Design modifications of a vacuum balance are also described.
Date: December 31, 1948
Creator: Knauss, H.P.
Partner: UNT Libraries Government Documents Department

Manual for the Portable Handheld Neutron Counter (PHNC) for Neutron Survey and the Measurement of Plutonium Samples

Description: We have designed a portable neutron detector for passive neutron scanning measurement and coincidence counting of bulk samples of plutonium. The counter will be used for neutron survey applications as well as the measurement of plutonium samples for portable applications. The detector uses advanced design {sup 3}He tubes to increase the efficiency and battery operated shift register electronics. This report describes the hardware, performance, and calibration for the system.
Date: November 1, 2005
Creator: Menlove, H.O.
Partner: UNT Libraries Government Documents Department

[sup 3]He neutron detector performance in mixed neutron gamma environments

Description: A test program of the performance of 3He neutron proportional detectors with varying gas pressures, and their response to lligh level gamma-ray exposure in a mixed neutrodgamma environment, ha$ been performed Our intent was to identie the optimal gas pressure to reduce the gamma-ray sensitivity of these detectors. These detectors were manufxtured using materials to minimize their gamma response. Earlier work focused on 3He fill pressures of four atmospheres and above, whereas the present work focuses on a wider range of pressures. Tests have shown that reducing the .filling pressure will M e r increase the gamma-ray dose range in which the detectors can be operated.
Date: January 1, 2002
Creator: Johnson, N. H. (Nathan H.) & Beddingfield, D. H. (David H.)
Partner: UNT Libraries Government Documents Department

Development of a high-efficiency neutron counter using novel materials

Description: Neutron detection efficiency is an important figure of merit for waste assay applications that must measure small quantities of material. It is also important for neutron coincidence counting and multiplicity counting because the detection of double- and triple-correlated events scales as the detection efficiency squared and cubed, respectively. Conventional thermal neutron detection systems typically employ {sup 3}He detector tubes embedded in polyethylene. The polyethylene moderates the neutrons so they can be detected by the {sup 3}He tubes. However, the hydrogen in the moderator also absorbs neutrons and reduces the diffusion length. We have extensively explored alternate designs that use both polyethylene and other industrial plastics with lower concentrations of hydrogen. In MCNP studies, we have achieved higher detection efficiency by using both polyethylene and other plastics in a hybrid design. In this paper we will present the design of a nominal 30%-efficient, 200-liter neutron counter that uses a hybrid design. We will show comparison results of this design compared to a standard polyethylene design. Finally, this counter has been constructed and tested, and was used in the Los Alamos waste assay course. We will show comparisons of the experimental results from this counter to the MCNP predictions.
Date: March 1, 1997
Creator: Pickrell, M.M.
Partner: UNT Libraries Government Documents Department

Use of the HPI Model 2080 pulsed neutron detector at the LANSCE complex - vulnerabilities and counting statistics

Description: The BPI Model 2080 Pulsed Neutron Detector has been used for over seven years as an area radiation monitor and dose limiter at the LANSCE accelerator complex. Operating experience and changing environments over this time have revealed several vulnerabilities (susceptibility to electrical noise, paralysis in high dose rate fields, etc.). Identified vulnerabilities have been connected; these modifications include component replacement and circuit design changes. The data and experiments leading to these modifications will be presented and discussed. Calibration of the instrument is performed in mixed static gamma and neutron source fields. The statistical characteristics of the Geiger-Muller tubes coupled with significantly different sensitivity to gamma and neutron doses require that careful attention be paid to acceptable fluctuations in dose rate over time during calibration. The performance of the instrument has been modeled using simple Poisson statistics and the operating characteristics of the Geiger-Muller tubes. The results are in excellent agreement with measurements. The analysis and comparison with experimental data will be presented.
Date: January 1, 1997
Creator: Jones, K.W. & Browman, A.
Partner: UNT Libraries Government Documents Department

A new neutron multiplicity counter for the measurement of impure plutonium metal at Westinghouse Savannah River Site

Description: A new neutron multiplicity counter has been designed, fabricated, characterized, and installed to assay impure plutonium metal buttons from the FB-line at the Westinghouse Savannah River Site (WSRS). This instrument incorporates the performance characteristics of the Pyrochemical or In-plant Multiplicity Counter with the package size of the Plutonium Scrap Multiplicity Counter. In addition, state-of-the-art features such as the derandomizer circuit and separate ring outputs have been added. The counter consists of 113 71-cm active length {sup 3}He tubes in a polyethylene moderator. Its efficiency for {sup 252}Cf is 57.8%, the highest of any multiplicity counter to date. Its die-away time is 50.4 ms and its deadtime is 50 ns. In this paper, the authors present the characterization data for the counter and the results of preliminary metal measurements at WSRS. They also discuss the new challenges the impure metal buttons from FB-line are presenting to the multiplicity counting technique.
Date: December 31, 1998
Creator: Langner, D.G.; Sweet, M.R.; Salazar, S.D.; Kroncke, K.E.; Baker, L.B. & Faison, D.M.
Partner: UNT Libraries Government Documents Department

Cross-calibration of neutron detectors for deuterium-tritium operation in TFTR

Description: During the initial deuterium-tritium experiments on TFTR, neutron emission was measured with {sup 235}U and {sup 238}U fission chambers, silicon surface barrier diodes, spatially collimated {sup 4}He proportional counters and ZnS scintillators, and a variety of elemental activation foils. The activation foils, {sup 4}He counters and silicon diodes can discriminate between 14 MeV and 2.5 MeV neutrons. The other detectors respond to both DD and DT neutrons but are more sensitive to the latter. The proportional counters, scintillators, and some of the fission chambers were calibrated absolutely, using a 14-MeV neutron generator positioned at numerous locations inside the TFTR vacuum vessel. Although the directly calibrated systems were saturated during the highest power deuterium-tritium operation, they allowed cross-calibration of less sensitive fission chambers and silicon diodes. The estimated absolute accuracy of the uncertainty-weighted mean of these cross-calibrations, combined with an independent calibration derived from activation foil determinations of total neutron yield, is {plus_minus}7%.
Date: March 1, 1995
Creator: Johnson, L.C.; Jassby, D.L.; Roquemore, A.L.; Strachan, J.D.; Barnes, C.W.; Duong, H.H. et al.
Partner: UNT Libraries Government Documents Department

Neutron Radiography and Computed Tomography at Oak Ridge National Laboratory

Description: The capability to perform neutron radiography and computed tomography is being developed at Oak Ridge National Laboratory. The facility will be located at the High Flux Isotope Reactor (HFIR), which has the highest steady state neutron flux of any reactor in the world. The Monte Carlo N-Particle transport code (MCNP), versions 4A and 4B, has been used extensively in the design phase of the facility to predict and optimize the operating characteristics, and to ensure the safety of personnel working in and around the blockhouse. Neutrons are quite penetrating in most engineering materials and can be useful to detect internal flaws and features. Hydrogen atoms, such as in a hydrocarbon fuel, lubricant or a metal hydride, are relatively opaque to neutron transmission. Thus, neutron based tomography or radiography is ideal to image their presence. The source flux also provides unparalleled flexibility for future upgrades, including real time radiography where dynamic processes can be observed. A novel tomography detector has been designed using optical fibers and digital technology to provide a large dynamic range for reconstructions. Film radiography is also available for high resolution imaging applications. This paper summarizes the results of the design phase of this facility and the potential benefits to science and industry.
Date: December 31, 1997
Creator: Raine, Dudley A. III; Hubbard, Camden R.; Whaley, Paul M.; Wright, Michael C. & Hutchinson, Donald P.
Partner: UNT Libraries Government Documents Department

A Fiber-Optic Neutron Detector for a Drive-By Scenario

Description: The measurement scenario of a neutron source driving by a detector has been evaluated. It is possible to use PNNL lithium-loaded fiber optics to measure the source, even at reasonably high speeds. A detector sufficient to detect the neutrons from the source at a high confidence level can be produced in a compact and robust configuration for a reasonable cost. In addition, the PNNL solution measures gamma-ray signals and will effectively add the function of a proximity sensor, lower the false-alarm rate, and allow discrimination between certain neutron source scenarios. Finally, the need for definition of confidence levels (both the method of computation and the required false alarm probability), emplacement form-factor, and electronic interface is required of a potential user to revise or customize the design outlined in this paper.
Date: March 30, 1999
Creator: Miley, H.S.
Partner: UNT Libraries Government Documents Department

Physics division. Progress report, January 1, 1995--December 31, 1996

Description: This issue of the Physics Division Progress Report describes progress and achievements in Physics Division research during the period January 1, 1995-December 31, 1996. The report covers the five main areas of experimental research and development in which Physics Division serves the needs of Los Alamos National Laboratory and the nation in applied and basic sciences: (1) biophysics, (2) hydrodynamic physics, (3) neutron science and technology, (4) plasma physics, and (5) subatomic physics. Included in this report are a message from the Division Director, the Physics Division mission statement, an organizational chart, descriptions of the research areas of the five groups in the Division, selected research highlights, project descriptions, the Division staffing and funding levels for FY95-FY97, and a list of publications and presentations.
Date: October 1, 1997
Creator: Stewart, M.; Bacon, D.S.; Aine, C.J. & Bartsch, R.R.
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

THE LANL NEUTRON SCIENCE CENTER TOF/PSD MODULE: STATUS AND PROGRESS

Description: This paper describes the progress and current status of a joint collaboration between Argonne National Laboratory (ANL) and the Los Alamos National Laboratory (LANL) Manuel Lujan Neutron Science Center (MLNSC) to develop and implement a Time-of-flight (TOF)/Position-Sensitive-Detector (PSD) VXI-based C-size neutron-event data-collection module. The LANL module, based on the ANL-developed hardware which uses field-programmable gate arrays (FPGAs) and analog-input-signal conditioning modules for a flexible topology capable of accepting either eight or 16 input channels, has been programmed and modified to incorporate more LANL-specific features such as improved peak detection, 24-bit time stamps, and 16-bit channel identification numbers which are all part of a 64-bit event record (2 by 32-bits wide). Using a backplane 10-MHz clock, timing resolution is {+-}50 ns. The module uses two, frame first-in-first-out buffers (FIFOs), each 2-kwords deep, to accumulate event data at up to 330 kEvents/sec during a frame until the host computer can read it out. One FIFO is read while the other is being filled. The module does not use the ANL token-passing configuration for accessing data. Rather, it uses direct logical-address and register-based addressing modes. To interface with analog signals from the neutron detectors, the module incorporates eight 72-pin single-inline-memory-module-size plug-in boards, called SIMs, which contain differential receivers, analog threshold comparators, and 8-bit analog-to-digital converters. A total of 16-analog channels are available if used in TOF mode, or eight channels if used in PSD mode.
Date: June 1, 1999
Creator: ROSE, C. & AL, ET
Partner: UNT Libraries Government Documents Department

Analysis of neutron scattering data: Visualization and parameter estimation

Description: Traditionally, small-angle neutron and x-ray scattering (SANS and SAXS) data analysis requires measurements of the signal and corrections due to the empty sample container, detector efficiency and time-dependent background. These corrections are then made on a pixel-by-pixel basis and estimates of relevant parameters (e.g., the radius of gyration) are made using the corrected data. This study was carried out in order to determine whether treatment of the detector efficiency and empty sample cell in a more statistically sound way would significantly reduce the uncertainties in the parameter estimators. Elements of experiment design are shortly discussed in this paper. For instance, we studied the way the time for a measurement should be optimally divided between the counting for signal, background and detector efficiency. In Section 2 we introduce the commonly accepted models for small-angle neutron and x-scattering and confine ourselves to the Guinier and Rayleigh models and their minor generalizations. The traditional approaches of data analysis are discussed only to the extent necessary to allow their comparison with the proposed techniques. Section 3 describes the main stages of the proposed method: visual data exploration, fitting the detector sensitivity function, and fitting a compound model. This model includes three additive terms describing scattering by the sampler, scattering with an empty container and a background noise. We compare a few alternatives for the first term by applying various scatter plots and computing sums of standardized squared residuals. Possible corrections due to smearing effects and randomness of estimated parameters are also shortly discussed. In Section 4 the robustness of the estimators with respect to low and upper bounds imposed on the momentum value is discussed. We show that for the available data set the most accurate and stable estimates are generated by models containing double terms either of Guinier's or Rayleigh's type. The optimal ...
Date: September 1, 1998
Creator: Beauchamp, J.J.; Fedorov, V.; Hamilton, W.A. & Yethiraj, M.
Partner: UNT Libraries Government Documents Department

Nondestructive assay tests of high-efficiency neutron counter (HENC) for waste assay and possible diversion scenario

Description: An advanced passive neutron counter, the high-efficiency neutron counter (HENC), has been used to measure plutonium content in 200-L waste drums. The HENC was designed with the {sup 252}Cf add-a-source (AS) feature to improve accuracy over a wide range of waste matrix materials. The current implementation allows for passive neutron coincidence counting, AS analysis, and multiplicity analysis. Passive neutron assay of typical waste containers is intrinsically more accurate than active neutron techniques because of the penetrability of the spontaneous fission neutrons originating from within the waste matrix. In addition, the HENC is designed as a slightly undermoderated detector to be less sensitive to low loading of hydrogen-bearing matrices. The following paper considers the applicability of three different nondestructive assay methods for analysis of waste drums and the flagging of possible diversions in waste drums. The {sup 252}Cf AS method, multiplicity counting, and a bounded-parameter multiplicity analysis are presented with areas of applicability.
Date: May 1, 1998
Creator: Mayo, D.R.; Menlove, H.O. & Pecos, J.M.
Partner: UNT Libraries Government Documents Department