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Scintillation Spectrometer System for Measuring Fast-Neutron Spectra in Beam Geometry

Description: A high-energy liquid-organic scintillation spectrometer system is described. This spectrometer was developed to measure neutron spectra in extracted beams from zero-power fast reactors. The highly efficient NE-213 scintillation solution was used as the neutron detection medium. Identification and removal of gamma-ray-induced events was accomplished using electronic pulse shape discrimination. Instrumentation used to process the discrete pulses stemming from neutron and gamma-ray interactions, within the scintillation solution, is described in detail. Evaluation of the system's performance is discussed for a gamma-ray discrimination ratio of nominally 1000:1, a total count-rate of 3000 cps, and a dynamic range corresponding to neutron energies from 1 to 10 MeV. Operation above 10 MeV is certainly possible. However, since the neutron flux above 10 MeV was negligible in the radiation fields of interest in this work, the operating characteristics of the spectrometer were not evaluated above 10 MeV. Neutron spectra are reported for extracted beam measurements made on ZPPR assembly 4, phase 2.
Date: May 1977
Creator: Simons, G. G.; Larson, J. M. & Reynolds, R. S.
Partner: UNT Libraries Government Documents Department

Analysis of the Energy of Neutrons Emerging from the Target by Means of Their Spatial Distribution

Description: As there is no accurate measurements of the energy distribution of neutrons emerging from large uranium blocks, it becomes of importance to see how much information of this kind can be derived from the slowing down distribution of the neutrons in a water tank.
Date: March 5, 1952
Creator: Brown, H.
Partner: UNT Libraries Government Documents Department

Measurement of the Slow Neutron Absorption Cross Section of Some Heavy Isotopes

Description: The following report investigates cross sections for the absorption of slow neutrons of heavy isotopes. The purpose of these measurements was to determine the cross section of an isotope of element 94 for the process of fission by the absorption of a slow neutron, relative to the cross section of U235 for the same process, that is, to measure R.
Date: 1943
Creator: English, Spofford Grady
Partner: UNT Libraries Government Documents Department

Direct Interaction Neutrons from 14-Mev Inelastic Neutron Scattering

Description: Abstract: "Neutron nonelastic cross sections measured at different detector biases have been used to determine the cross sections for inelastically scattering 14 Mev neutrons into 9- to 14-Mev energy range. The cross section for producing these high energy neutrons, which may be attributed to direct interaction processes, is roughly 10% of the nonelastic cross section, for all elements. A comparison is made with data of Coon and co workers, who measured angular distributions for the same high-energy inelastically scattered-neutron group."
Date: May 19, 1958
Creator: MacGregor, Malcolm H.
Partner: UNT Libraries Government Documents Department

Notes on Predicted Fast Neutron Dose from Thermal Neutron Data in Water

Description: Abstract: "An appropriate method has been applied to predict fast neutron dosimeter data from thermal neutron measurements. Results are compared with actual dosimeter data and it is concluded that the method presented gives a good approximation for fast neutron dose. This is important since in many previous experiments fast neutron dosimeter data had not been taken, but thermal neutron data had been obtained."
Date: 1953
Creator: Stone, Henry E.
Partner: UNT Libraries Government Documents Department

Thermal neutron imaging support with other laboratories BL06-IM-TNI

Description: The goals of this project are: (1) detect and locate a source of thermal neutrons; (2) distinguish a localized source from uniform background; (3) show shape and size of thermalizing material; (4) test thermal neutron imager in active interrogation environment; and (5) distinguish delayed neutrons from prompt neutrons.
Date: June 17, 2008
Creator: Vanier, P. E.
Partner: UNT Libraries Government Documents Department

SURVEY METHODS FOR NEUTRON FIELDS

Description: To one whose responsibility it is to make evaluations of the degree of hazard existing in the radiation field of a nuclear accelerator or a nuclear reactor, the valid estimate of the contribution of neutrons to such a field is of considerable importance. The degree of difficulty of such a measurement depends strongly upon the information desired - whether (1) simply the presence of 'slow' and 'fast' neutrons in significant numbers is in question, or (2) a measure of flux densities within known energy intervals is required, or (3) a direct estimate of the specific rate of energy absorption due to neutron-produced effects in a given medium is desired. The importance of securing trustworthy estimates of the neutron field can be appreciated by recalling that the biological damage due to a given amount of ionization produced in biological tissue by effects due to neutrons is estimated to be several times the damage due to a similar amount of ionization produced by X-rays or gamma rays. This 'relative biological effectiveness' must be evaluated by carefully controlled animal experiments. Its value appears to range from about 2.5 for slow neutrons to abount 10 for fast and high energy neutrons. Of course the value obtained may also be a function of the particular biological variable under observations, and from some experiments a value as high as 20 for fast neutrons may be indicated.
Date: January 11, 1952
Creator: Moyer, B.J.
Partner: UNT Libraries Government Documents Department

Gamma Ray Response of a CsI(T1) Crystal to 14 Mev Neutrons

Description: The purpose of this paper is to study the possible excited states in the nucleus of Cs133. At North Texas State College a 100-Kev Cockcroft-Walton accelerator has been constructed for use as a neutron source for exciting various nuclei and for studying the gamma spectra obtained to determine their energy levels.
Date: August 1958
Creator: Young, Jack Carter
Partner: UNT Libraries

Pile Theory Notes for M.I.T. Seminar

Description: This report discusses topics relating to pile theory, focusing specifically on describing a nuclear chain reacting system. Topics covered include the time dependence of neutron density, controlling chain reacting boxes, and the behavior of neutrons in a pile.
Date: 1946
Creator: Feld, T. T. & Friedman, Francis L. (Francis Lee), 1918-
Partner: UNT Libraries Government Documents Department

Modeling of Fission Neutrons as a Signature for Detection of Highly Enriched Uranium

Description: We present the results of modeling intended to evaluate the feasibility of using neutrons from induced fission in highly enriched uranium (HEU) as a means of detecting clandestine HEU, even when it is embedded in absorbing surroundings, such as commercial cargo. We characterized radiation from induced fission in HEU, which consisted of delayed neutrons at all energies and prompt neutrons at energies above a threshold. We found that for the candidate detector and for the conditions we considered, a distinctive HEU signature should be detectable, given sufficient detector size, and should be robust over a range of cargo content. In the modeled scenario, an intense neutron source was used to induce fissions in a spherical shell of HEU. To absorb, scatter, and moderate the neutrons, we place one layer of simulated cargo between the source and target and an identical layer between the target and detector. The resulting neutrons and gamma rays are resolved in both time and energy to reveal the portion arising from fission. We predicted the dominant reaction rates within calcium fluoride and liquid organic scintillators. Finally, we assessed the relative effectiveness of two common neutron source energies.
Date: March 9, 2004
Creator: Wolford, J K; Frank, M I & Descalle, M
Partner: UNT Libraries Government Documents Department

The Spatial Distribution of Neutrons Slowed Down by Elastic Collisions

Description: Technical report discussion of the complicated problem of the spatial distribution of slowed down neutrons. The introduction covers the current research on the topic. The following chapters cover the topics: (1) approximate treatment and its limitations, (2) age-velocity distribution, (3) general scheme of treatment based on transport equation, (4) Fermi's one-dimensional model, (5) moments, (6) remarks about the distribution function, and (7) point source.
Date: June 11, 1946
Creator: Placzek, G. (George), 1905-1955.
Partner: UNT Libraries Government Documents Department

MUFT Revision : A Fast Neutron Spectrum Code for the IBM-650

Description: Report documenting the MUFT-R program, which is "designed to solve the fast neutron transport problem for general mixtures of elements and obtain sets of average fast neutron diffusion constants for specified portions of the fast energy spectrum" (p. iii). Includes detailed derivations of utilized equations.
Date: 1962
Creator: Grimesey, Robert A.; Mullen, Frank Edward & Gannon, L. J.
Partner: UNT Libraries Government Documents Department

A Kinematically Beamed, Low Energy Pulsed Neutron Source for Active Interrogation

Description: We are developing a new active interrogation system based on a kinematically focused low energy neutron beam. The key idea is that one of the defining characteristics of SNM (Special Nuclear Materials) is the ability for low energy or thermal neutrons to induce fission. Thus by using low energy neutrons for the interrogation source we can accomplish three goals, (1) Energy discrimination allows us to measure the prompt fast fission neutrons produced while the interrogation beam is on; (2) Neutrons with an energy of approximately 60 to 100 keV do not fission 238U and Thorium, but penetrate bulk material nearly as far as high energy neutrons do and (3) below about 100keV neutrons lose their energy by kinematical collisions rather than via the nuclear (n,2n) or (n,n') processes thus further simplifying the prompt neutron induced background. 60 keV neutrons create a low radiation dose and readily thermal capture in normal materials, thus providing a clean spectroscopic signature of the intervening materials. The kinematically beamed source also eliminates the need for heavy backward and sideway neutron shielding. We have designed and built a very compact pulsed neutron source, based on an RFQ proton accelerator and a lithium target. We are developing fast neutron detectors that are nearly insensitive to the ever-present thermal neutron and neutron capture induced gamma ray background. The detection of only a few high energy fission neutrons in time correlation with the linac pulse will be a clear indication of the presence of SNM.
Date: October 7, 2004
Creator: Dietrich, D; Hagmann, C; Kerr, P; Nakae, L; Rowland, M; Snyderman, N et al.
Partner: UNT Libraries Government Documents Department

REACTOR PHYSICS CONSTANTS

Description: This compilation of reactor physics constants, based on data available up to March 15, 1958, is the first publication of the Reactor Physics Constants Center (RPCC). The primary objective of the RPCC is the periodic compilation of the latest and best values of the constants, recipes, formulas, etc., which are necessary to calculate reactor characteristics. (W. D.M.)
Date: January 1, 1958
Partner: UNT Libraries Government Documents Department

Thermal Neutron Backscatter Imaging

Description: Objects of various shapes, with some appreciable hydrogen content, were exposed to fast neutrons from a pulsed D-T generator, resulting in a partially-moderated spectrum of backscattered neutrons. The thermal component of the backscatter was used to form images of the objects by means of a coded aperture thermal neutron imaging system. Timing signals from the neutron generator were used to gate the detection system so as to record only events consistent with thermal neutrons traveling the distance between the target and the detector. It was shown that this time-of-flight method provided a significant improvement in image contrast compared to counting all events detected by the position-sensitive {sup 3}He proportional chamber used in the imager. The technique may have application in the detection and shape-determination of land mines, particularly non-metallic types.
Date: October 16, 2004
Creator: Vanier, P.; Forman, L.; Hunter, S.; Harris, E. & Smith, G.
Partner: UNT Libraries Government Documents Department

Event-by-Event Study of Prompt Neutrons from 239Pu

Description: Employing a recently developed Monte Carlo model, we study the fission of {sup 240}Pu induced by neutrons with energies from thermal to just below the threshold for second chance fission. Current measurements of the mean number of prompt neutrons emitted in fission, together with less accurate measurements of the neutron energy spectra, place remarkably fine constraints on predictions of microscopic calculations. In particular, the total excitation energy of the nascent fragments must be specified to within 1 MeV to avoid disagreement with measurements of the mean neutron multiplicity. The combination of the Monte Carlo fission model with a statistical likelihood analysis also presents a powerful tool for the evaluation of fission neutron data. Of particular importance is the fission spectrum, which plays a key role in determining reactor criticality. We show that our approach can be used to develop an estimate of the fission spectrum with uncertainties several times smaller than current experimental uncertainties for outgoing neutron energies of less than 2 MeV.
Date: January 15, 2010
Creator: Vogt, R; Randrup, J; Pruet, J & Younes, W
Partner: UNT Libraries Government Documents Department

Comparative Effectiveness and Additivity of Fission Neutrons Gamma Rays and Beta Rays of Drosphila Eggs

Description: From abstract: "Some investigations have been made to ascertain the similarity of the mechanism of action of radiation which are different in their specific ionization. A suggested approach was to determine if the energies absorbed from the different types of radiation are additive in their lethal effects on biological objects. In an attempt to determine the additivity of ionizing radiation various dose combinations of fast neutrons, gamma rays and beta rays were administered to Drosophila eggs. These test objects were chosen because their dimensions are such that they tend to absorb these three radiations uniformly throughout their volume. Although the three radiations were found to vary in their biological effectiveness, per unit energy absorbed, all three were shown to be completely additive in their lethal effect on these organisms."
Date: February 1946
Creator: Stapleton, G. E. & Zirkle, Raymond E. (Raymond Elliot), 1902-1988
Partner: UNT Libraries Government Documents Department

A Simple Calibration and Checking Facility for Fast and Slow Neutron Detectors

Description: From introduction: The principal work described below is the development and tests of a slow neutron flux generator based on a generator developed at the University of California (UCRL 8359, W. Patterson, Roger Wallace, "A Method of Calibrating Slow Neutron Detectors"). It is shown that a tolerance flux density of slow neutrons results within a cubical cavity 15 inches on an edge with 4-inch-thick walls of water or paraffin wax when a plutonium-beryllium source emitting about 7 million neutrons per second is placed within the cavity according to a standard procedure. The principle on which the generator is based is that the fast neutrons from the source are slowed to near thermal velocities by scattering from the cavity walls. (Although the principal interest is in the slow flux, a primary fast flux is present at any point depending on the inverse square of the distance from the source.) The variation of slow neutron flux density over the walls of the cavity is unimportant for the calibration of thermal neutron detectors which follow a 1/v or 1/E response law (where v and E are the neutron velocity and energy), so that the detector is sensitive mainly to the slow neutron flux. As stated, the method provides a slow neutron flux density (instead of the neutron density only) so that a calibration for detectors placed within the cavity can be given either in terms of flux density of slow neutrons or, by simple conversion, in terms of dose-rate.
Date: January 28, 1959
Creator: Redmond, A. H.
Partner: UNT Libraries Government Documents Department

Chemical Engineering Division Fast-Neutron Dosimetry, Annual Report: July 1975-June 1976

Description: One of the objectives of the Dosimetry and Damage Analysis Center is to provide standardized dosimetry technology for materials-study programs within the ERDA Division of Magnetic Fusion Energy. Current efforts have included characterization of neutron environments in terms of fluence and spectral distribution for materials experiments conducted at the Lawrence Livermore Laboratory's (LLL) Rotating Target Neutron Source and at the LLL-Davis Cyclograaff. Environment characterization efforts at Brookhaven National Laboratory's High Flux Beam Reactor and those pertaining to an enriched-uranium converter for the ANL CP-5 reactor are also described. The capability of calculating material radiation damage parameters associated with these neutron environments is demonstrated. Average fission yields determined from two fast-neutron irradiations and one thermal-neutron irradiation are compiled for laboratories participating in the inter-laboratory Reaction Rate program. These results are in excellent agreement with literature values. Progress on the development of boron-10 and lithium-6-loaded liquid scintillation detectors for detecting very low intensity neutrons is presented. Material purification tests and performance tests of scintillation mixtures are described.
Date: 1976?
Creator: Heinrich, R. R.; Greenwood, L. R.; Kennerley, R. J.; Chellew, N. R.; Popek, R. J.; Malewicki, Russell et al.
Partner: UNT Libraries Government Documents Department

Improving Hiroshima Air-Over-Ground Thermal/Epithermal Activation Calculations Using a MUSH Model to Show the Importance of Local Shielding

Description: Achieving agreement between measured and calculated neutron activation data resulting from Hiroshima and Nagasaki A-bomb detonations has been a major problem since the early 1980's. This has been particularly true for the materials that are activated by thermal and epithermal neutrons. Since thermal and epithermal neutrons are not transported very far from the weapon, the local shielding environment around the measurement location can be very important. A set of calculations incorporating an average density local-environment material (mush) has been made to demonstrate that the local environment plays an important role in the calculation-measurement agreement process. The optimum solution would be to include the local environment in all thermal neutron response calculations.
Date: February 14, 2002
Creator: Pace, J.V.
Partner: UNT Libraries Government Documents Department
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