194 Matching Results

Search Results

Advanced search parameters have been applied.

Integration of TGS and CTEN assays using the CTEN{_}FIT analysis and databasing program

Description: The CTEN{_}FIT program, written for Windows 9x/NT in C++, performs databasing and analysis of combined thermal/epithermal neutron (CTEN) passive and active neutron assay data and integrates that with isotopics results and gamma-ray data from methods such as tomographic gamma scanning (TGS). The binary database is reflected in a companion Excel database that allows extensive customization via Visual Basic for Applications macros. Automated analysis options make the analysis of the data transparent to the assay system operator. Various record browsers and information displays simplified record keeping tasks.
Date: May 1, 2000
Creator: Estep, R.
Partner: UNT Libraries Government Documents Department

Evidence of water ice near the lunar poles

Description: Lunar Prospector epithermal neutron data were studied to evaluate the probable chemical state of enhanced hydrogen, [H], reported previously to be near both lunar poles [1,2]. Improved versions of thermal and epithermal neutron data were developed for this purpose. Most important is the improved spatial resolution obtained by using shortened integration times. A new data set was created, Epi* = [Epithermal - 0.057 x Thermal], to reduce effects of composition variations other than those due to hydrogen. The Epi* counting rates are generally low near both lunar poles and high over terrane near recent impact events such as Tycho and Jackson. However, other lunar features are also associated with high Epi* rates, which represent a wide range of terrane types that seem to have little in common. If we postulate that one property all bright Epi* features do have in common is low [H], then measured Epi* counting rates appear to be quantitatively self consistent. If we assume that [H]=O above the top 98th percentile of Epi* counting rates at 2{sup o} x 2{sup o} spatial resolution, then [H]{sub ave} = 55 ppm for latitudes equatorward of [75{sup o}]. This value is close to the average found in returned lunar soil samples, [H]{sub ave} {approx} 50 ppm [3]. Using the foregoing physical interpretation of Epi* counting rates, we find that the Epi* counts within most of the large craters poleward of {+-}70{sup o} are higher, and therefore [H] is lower, than that in neighboring inter-crater plains, as shown in Figure 1. Fourteen of these craters that have areas larger than the LP epithermal spatial resolution (55 km diameter at 30 km altitude), were singled out for study. [H] is generally found to increase with decreasing distance from the poles (hence decreasing temperature). However, quantitative estimates of the diffusivity of hydrogen ...
Date: January 1, 2001
Creator: Feldman, W. C. (William C.); Maurice, S. (Sylvestre); Lawrence, David J. (David Jeffery),; Little, R. C. (Robert C.); Lawrence, S. L. (Stefanie L.); Gasnault, O. M. (Olivier M.) et al.
Partner: UNT Libraries Government Documents Department

Photoneutron effects on pulse reactor kinetics for the Annular Core Research Reactor (ACRR).

Description: The Annular Core Research Reactor (ACRR) is a swimming-pool type pulsed reactor that maintains an epithermal neutron flux and a nine-inch diameter central dry cavity. One of its uses is neutron and gamma-ray irradiation damage studies on electronic components under transient reactor power conditions. In analyzing the experimental results, careful attention must be paid to the kinetics associated with the reactor to ensure that the transient behavior of the electronic device is understood. Since the ACRR fuel maintains a substantial amount of beryllium, copious quantities of photoneutrons are produced that can significantly alter the expected behavior of the reactor power, especially following a reactor pulse. In order to understand these photoneutron effects on the reactor kinetics, the KIFLE transient reactor-analysis code was modified to include the photoneutron groups associated with the beryllium. The time-dependent behavior of the reactor power was analyzed for small and large pulses, assuming several initial conditions including following several pulses during the day, and following a long steady-state power run. The results indicate that, for these types of initial conditions, the photoneutron contribution to the reactor pulse energy can have a few to tens of percent effect.
Date: June 1, 2009
Creator: Parma, Edward J., Jr.
Partner: UNT Libraries Government Documents Department

Study of parity nonconservation with epithermal neutrons

Description: The authors describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C.S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized {sup 60}Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the - strong interaction can contribute, we expect much smaller asymmetries, of order 10{sup -7}.
Date: September 1996
Creator: Seestrom, S. J.; Bowman, J. D.; Knudson, J. N. & Yuan, V.
Partner: UNT Libraries Government Documents Department

A Monte Carlo model system for core analysis and epithermal neutron beam design at the Washington State University Radiation Center

Description: The Monte Carlo Model System (MCMS) for the Washington State University (WSU) Radiation Center provides a means through which core criticality and power distributions can be calculated, as well as providing a method for neutron and photon transport necessary for BNCT epithermal neutron beam design. The computational code used in this Model System is MCNP4A. The geometric capability of this Monte Carlo code allows the WSU system to be modeled very accurately. A working knowledge of the MCNP4A neutron transport code increases the flexibility of the Model System and is recommended, however, the eigenvalue/power density problems can be run with little direct knowledge of MCNP4A. Neutron and photon particle transport require more experience with the MCNP4A code. The Model System consists of two coupled subsystems; the Core Analysis and Source Plane Generator Model (CASP), and the BeamPort Shell Particle Transport Model (BSPT). The CASP Model incorporates the S({alpha}, {beta}) thermal treatment, and is run as a criticality problem yielding, the system eigenvalue (k{sub eff}), the core power distribution, and an implicit surface source for subsequent particle transport in the BSPT Model. The BSPT Model uses the source plane generated by a CASP run to transport particles through the thermal column beamport. The user can create filter arrangements in the beamport and then calculate characteristics necessary for assessing the BNCT potential of the given filter want. Examples of the characteristics to be calculated are: neutron fluxes, neutron currents, fast neutron KERMAs and gamma KERMAs. The MCMS is a useful tool for the WSU system. Those unfamiliar with the MCNP4A code can use the MCMS transparently for core analysis, while more experienced users will find the particle transport capabilities very powerful for BNCT filter design.
Date: May 1, 1996
Creator: Burns, T.D. Jr.
Partner: UNT Libraries Government Documents Department

Target studies for accelerator-based boron neutron capture therapy

Description: Two new concepts, NIFTI and DISCOS, are described. These concepts enable the efficient production of epithermal neutrons for BNCT (Boron Neutron Capture Therapy) medical treatment, utilizing a low current, low energy proton beam impacting on a lithium target. The NIFTI concept uses an iron layer that strongly impedes the transmission of neutrons with energies above 24 KeV. Lower energy neutrons readily pass through this iron ``filter``, which has a deep ``window`` in its scattering cross section at 24 KeV. The DISCOS concept uses a rapidly rotating, high g disc to create a series of thin ({approximately} 1 micron thickness) liquid lithium targets in the form of continuous films through which the proton beam passes. The average energy lost by a proton as it passes through a single target is small, approximately 10 KeV. Between the targets, the proton beam is reaccelerated by an applied DC electric field. The DISCOS approach enables the accelerator -- target facility to operate with a beam energy only slightly above the threshold value for neutron production -- resulting in an output beam of low-energy epithermal neutrons -- while achieving a high yield of neutrons per milliamp of proton beam current.
Date: March 1, 1996
Creator: Powell, J.R.; Ludewig, H.; Todosow, M. & Reich, M.
Partner: UNT Libraries Government Documents Department

A study of the concept of a fission-plate converter as a source for an epithermal neutron beam

Description: It has been suggested that a Fission-Plate Converter (FPC) at a reactor can enhance the intense of an epithermal neutron beam produced by the reactor. By computer modeling, this concept has been applied to two sets of reactors to study how effective a FPC might be. The first set of reactors contains high-powered research reactors and is represented by the Missouri University Research Reactor and the Georgia Institute of Technology Research Reactor. The second set combines the FPC into the core of a low-powered reactor, yielding a thin, large area, reactor that we call a slab reactor. For these reactors, epithermal fluxes above 1 x 10{sup 9} n/cm{sup 2}{center_dot}sec are predicted while the fast-neutron doses per epithermal neutron are < 3 x 10{sup -11} cGy{center_dot}cm{sup 2}/n.
Date: December 31, 1994
Partner: UNT Libraries Government Documents Department

Development of an accelerator-based BNCT facility at the Berkeley Lab

Description: An accelerator-based BNCT facility is under construction at the Berkeley Lab. An electrostatic-quadrupole (ESQ) accelerator is under development for the production of neutrons via the {sup 7}Li(p,n){sup 7}Be reaction at proton energies between 2.3 and 2.5 MeV. A novel type of power supply, an air-core coupled transformer power supply, is being built for the acceleration of beam currents exceeding 50 mA. A metallic lithium target has been developed for handling such high beam currents. Moderator, reflector and neutron beam delimiter have extensively been modeled and designs have been identified which produce epithermal neutron spectra sharply peaked between 10 and 20 keV. These. neutron beams are predicted to deliver significantly higher doses to deep seated brain tumors, up to 50% more near the midline of the brain than is possible with currently available reactor beams. The accelerator neutron source will be suitable for future installation at hospitals.
Date: March 1, 1998
Creator: Ludewigt, B.A.; Bleuel, D.; Chu, W.T.; Donahue, R.J.; Kwan, J.; Reginato, L.L. 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


Description: The mathematical formulation of the subcritical reactor with extraneous sources is presented in detail. The solutions are presented for a two-group approximation including epithermal fission and the relationship to the usual critical reactor problem is discussed. Application of the equations to an arbitrarily complicated geometry is outlined, and an IBM-7090 program for the solution in a bare cylindrical reactor is described. (auth)
Date: March 13, 1962
Creator: Preskitt, C.A.
Partner: UNT Libraries Government Documents Department

Enhancement of the Epithermal Neutron Beam at the Brookhaven Medical Research Reactor

Description: Improvements for the Brookhaven Medical Research Reactor (BMRR) epithermal neutron beam have been evaluated by MCNP calculations and measurements. Different dosimetric measurements have been made after one fuel element was in place of the graphite stringer in the core. Measurements show an 18% increase of beam intensity without reducing the beam quality. These results are consistent with the predictions of an MCNP calculation. Major changes to enhance the beam include rearranging the fuel elements in the core, placing aluminum pellets in the moderator tank C, redesigning the moderator assembly, replacing the outer bismuth by lead plus 0.05% atomic number density of {sup 6}Li, and modifying the irradiation port to accommodate an air indentation. The MCNP calculated values for the present and new designs were compared to demonstrate the improvements. The results show that the epithermal flux can be increased by 80% at the irradiation port. The neutron dose per epithermal neutron can be reduced by 30%. The beam directionality can be improved by 7%.
Date: 1992~
Creator: Liu, Hungyuan B.; Brugger, Robert M. & Rorer, David C.
Partner: UNT Libraries Government Documents Department

Summing up: The physics of NCT

Description: Neutron Capture Therapy (NCT) is a binary system for treating tumors in which both an agent, usually B-10, and thermal neutrons are directed to a tumor where they combine and release lethal radiation. Directing the agent to the tumor is mainly a chemistry and biology problem, while the production, targeting and effects of the neutrons is mainly a physics problem. This paper briefly describes the, physics side of NCT as presented at this symposium, the neutron beams, the dosimetry and treatment planning, and the element identification. The development of the physical tools and methods are not now limiting the successful demonstration of NCT. Several epithermal neutron beams are available, dosimetry methods are in hand, and treatment planning methods can be ready when required. Methods of identifying elements have been demonstrated, but are not yet widely accessible. New methods could supply valuable additional information about the quantity and location of NCT elements, particularly on the microscopic scale and in vivo.
Date: April 1, 1993
Creator: Brugger, R. M.
Partner: UNT Libraries Government Documents Department

Optimization of an accelerator-based epithermal neutron source for neutron capture therapy

Description: A modeling investigation was performed to choose moderator material and size for creating optimal epithermal neutron beams for BNCT based on a proton accelerator and the 7Li(p,n)7Be reaction as a neutrons source. An optimal configuration is suggested for the beam shaping assembly made from polytetrafluoroethylene and magnesium fluorine. Results of calculation were experimentally tested and are in good agreement with measurements.
Date: February 20, 2004
Creator: Kononov, O.E.; Kononov, V.N.; Bokhovko, M.V.; Korobeynikov, V.V.; Soloviev, A.N. & Chu, W.T.
Partner: UNT Libraries Government Documents Department


Description: Effective cutoff energies for point l/v absorbers inside of spherical and cylindrical cadmium filters have been calculated for thermal reactor neutrons. The neutron spectrum was assumed to consist of a Maxwellian plus a 1/E component, and the parameters varied were the thickness of filter, the Maxwellian temperature and the Maxwellian to 1/E flux ratio. Because of the sensitivity of the effective cutoff to Maxwellian flux parameters for thin filters it is recommended that filter thicknesses of about 40 mils be used. Forty mil filters show effective cutoffs at about 0.50 to 0.55 ev for temperatures up to about 500 ction prod- A (or about 0.045 ev). Effective cutoff energies for boron filters were also calculated for purposes of comparison. The cutoffs for cylindrical cadmium filters should be applicable to a properly designed experimental facility. (auth)
Date: March 11, 1960
Creator: Stoughton, R.W.; Halperin, J. & Lietzke, M.P.
Partner: UNT Libraries Government Documents Department


Description: A limited investigation was made of possible reactor configurations that would contuin a region having a high intermediate-energy (1 to 10/sup 3/ ev) flux relative to the fast and thermal flux. All calculations were performed with a multigroup, multiregion reactor program (GNU-II). Consideration of a single- region, unreflected sphere indicated that the desired flux distribution could not be generated in a region containing fuel because of its resonance absorption. A flux-trap configuration was investigated with a cyclindrical iron core surrounded by a fuel annulus. Calculations indicated that the fast flux would not be depressed significantly in the central region unless the dimensions were large. Consideration was then given to an iron reflector for an infinite slab reactor. Good agreement was obtained between reported experimental and calculated relaxation lengths for the flux at different energies. It was found that the desired flux-energy distribution was approached at a point some 20 to 30 cm ixto the iron slab from the fuel; however, the magnitude of the flux relative to that in the fuel region was low. (auth)
Date: September 1, 1959
Creator: Sanders, J.P.
Partner: UNT Libraries Government Documents Department


Description: The results of a study are presented which provided additional experimental-loop irradiation space for the AECDRD testing program. It was a premise that the experiments allocated to this reactor were those which could not be accommodated in the MTR, ETR, or in existing commercial test reactors. To accomplish the design objectives called for a reactor producing perturbed neutron fluxes exceeding 1O/sup 15/ thermal n/cm/sup 2/-sec and 1.5 x 1O/sup 15/ epithermal n/cm/sup 2/-sec. To accommodate the experimental samples, the reactor fuel core is four feet long in the direction of experimental loops. This is twice the length of the MTR core and a third longer than the ETR core. The vertical arrangement of reactor and experiments permits the use of loops penetrating the top cap of the reactor vessel running straight and vertically through the reactor core. The design offers a high degree of accessibility of the exterior portions of the experiments and offers very convenient handling and discharge of experiments. Since the loops are to be integrated into the reactor design and the in-pile portions installed before reactor start-up, it is felt that many of the problems encountered in MTR and ETR experience will cease to exist. Installation of the loops prior to startup will have an added advantage in that the flux variations experienced in experiments in ETR every time a new loop is installed will be absent. The Advanced Test Reactor has a core configuration that provides essentially nine flux-trap regions in a geometry that is almost optimum for cylindrical experiments. The geometry is similar to that of a fourleaf clover with one flux trap in each leaf, one at the intersection of the leaves, and one between each pair of leaves. The nominal power level is 250 Mw. The study was carried out in enough detail ...
Date: November 1, 1960
Creator: deBoisblanc, D.R. et al
Partner: UNT Libraries Government Documents Department


Description: A description is given of measurements required to determine the values of thermal utilization for U-10 wt.% Mo fuel elements in hexagonal lattices of three different spacings. The discussion includes a description of the lattice cells, and a graphical representation of the neutronflux distributions in the cell materials. Epi-cadmium neutron-flux distributions and cadmium ratios for each lattice cell studied are included. (auth)
Date: December 19, 1960
Creator: Hillig, O.R.
Partner: UNT Libraries Government Documents Department

Mid-latitude composition of mars from thermal and epithermal neutrons

Description: Epithermal neutron data acquired by Mars Odyssey have been analyzed to determine global maps of water-equivalent hydrogen abundance. By assuming that hydrogen was distributed uniformly with depth within the surface, a map of minimum water abundance was obtained. The addition of thermal neutrons to this analysis could provide information needed to determine water stratigraphy. For example, thermal and epithermal neutrons have been used together to determine the depth and abundance of waterequivalent hydrogen of a buried layer in the south polar region. Because the emission of thermal neutrons from the Martian surface is sensitive to absorption by elements other than hydrogen, analysis of stratigraphy requires that the abundance of these elements be known. For example, recently published studies of the south polar region assumed that the Mars Pathfinder mean soil composition is representative of the regional soil composition, This assumption is partially motivated by the fact that Mars appears to have a well-mixed global dust cover and that the Pathfinder soil composition is representative of the mean composition of the Martian surface. In this study, we have analyzed thermal and epithermal neutron data measured by the neutron spectrometer subsystem of the gamma ray spectrometer to determine the spatial distribution of the composition of elements other than hydrogen. We have restricted our analysis to mid-latitude regions for which we have corrected the neutron counting data for variations in atmospheric thickness.
Date: January 1, 2003
Creator: Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Elphic, R. C. (Richard C.); Boynton, W. V. (William V.); Bish, D. L. (David L.); Vaniman, D. T. (David T.) et al.
Partner: UNT Libraries Government Documents Department

Growth of C02 frost thickness near Chasma Borealis during northern winter and spring.

Description: Epithermal neutron fluxes measured using the Neutron Spectrometer component of the Mars OdysscNGamma-Ray Spectrometer suite of instruments were studied to determ i ne the spatial and temporal dependence of CO2 frost cover of the nor t h polar cap for L, between 329 and 99 arcoccntric longitude. This time period spans the la t e northern xvinter through summer solstice . In the absence of a CO, cuvcr, the entire basement terrain p o l eward of about +55 latitude is vm, rich in I1 :0 . The consequent enhanced abundance of hydrogen in near-surface soils leads to an anomaluusly low flux of oumardly leaking cpithcrmal ncutrons, wh i ch is a prominent signatu r e of epi t hermal neutron maps measured after about L, = 90 . Because the epithermal neutron flux rises monotonically w i t h increasing thickness of t h e CO . fros t cover, it provides a robust measure of the CO2 thickness in space and time .
Date: January 1, 2003
Creator: Feldman, W. C. (William C.); Boynton, W. V. (William V.); Prettyman, T. H. (Thomas H.); Kelly, N. & Maurice, S. (Sylvestre)
Partner: UNT Libraries Government Documents Department