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Analysis of the burping behavior of the cold solid methane moderator at IPNS (Intense Pulsed Neutron Source)

Description: Examination of the cold solid methane moderator at IPNS (Model II) revealed that a circumferential weld failed due to high internal pressure, such as would be caused by thermal expansion of solid methane or the release of Hydrogen gas upon spontaneous heating. This weld is the main object of current attention for a design of a replacement. The present paper deals with the processes which lead to the burping behavior and outlines the analysis of some of the consequences. The purpose is to determine conditions under which the system can operate at the lowest possible temperature, avoiding the problems experienced to data.
Date: January 1, 1986
Creator: Carpenter, J.M. & Walter, U.
Partner: UNT Libraries Government Documents Department

Technical concepts for a long-wavelength target station for the Spallation Neutron Source.

Description: The Spallation Neutron Source (SNS), a major new user facility for materials research funded by the U.S. Department of Energy (DOE), is under construction at Oak Ridge National Laboratory (ORNL), see the Spallation Neutron Source web site at: www.sns.gov/aboutsns/source/htm. The SNS will operate at a proton beam power of 1.4 MW delivered in short pulses at 60 Hz; this power level is an order of magnitude higher than that of the current most intense pulsed spallation neutron facility in the world, ISIS at the Rutherford-Appleton Laboratory in the United Kingdom: 160 kW at 50 Hz. When completed in 2006, the SNS will supply the research community with neutron beams of unprecedented intensity and a powerful, diverse instrument suite with exceptional capabilities. Together, these will enable a new generation of experimental studies of interest to chemists, condensed matter physicists, biologists, materials scientists, and engineers, in an ever-increasing range of applications. The Long-Wavelength Target Station (LWTS) complements the High-Power Target Station (HPTS) facility, which is already under construction, and will leverage the significant investment in the remainder of the complex, providing important new scientific opportunities. The fully equipped SNS will offer capabilities for neutron scattering studies of the structure and dynamics of materials with sensitivity, resolution, dynamic range, and speed that are unparalleled in the world.
Date: December 4, 2002
Creator: Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Pulsed spallation neutron sources

Description: This paper reviews the early history of pulsed spallation neutron source development ar Argonne and provides an overview of existing sources world wide. A number of proposals for machines more powerful than currently exist are under development, which are briefly described. The author reviews the status of the Intense Pulsed Neutron Source, its instrumentation, and its user program, and provide a few examples of applications in fundamental condensed matter physics, materials science and technology.
Date: May 1, 1996
Creator: Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

The Delayed-Neutron Fraction in a Pulsed Spallation Neutron Source

Description: The fraction of delayed neutrons beta in slow-neutron beams from a uranium-238 pulsed spallation neutron source is 0.0053 for 300 MeV protons. This measurement appears to be the first one of this quantity. The result indicates that, for most classes of measurements, the delayed-neutron background in time-of-flight instruments will be unimportant, and places constraints on the physics description of spallation targets. The measurement was performed at the prototype pulsed spallation neutron source, ZING-P', at Argonne National laboratory.
Date: February 1980
Creator: Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Report on the international workshop on cold moderators for pulsed neutron sources.

Description: The International Workshop on Cold Moderators for Pulsed Neutron Sources resulted from the coincidence of two forces. Our sponsors in the Materials Sciences Branch of DOE's Office of Energy Research and the community of moderator and neutron facility developers both realized that it was time. The Neutron Sources Working Group of the Megascience Forum of the Organization for Economic Cooperation and Development offered to contribute its support by publishing the proceedings, which with DOE and Argonne sponsorship cemented the initiative. The purposes of the workshop were: to recall and improve the theoretical groundwork of time-dependent neutron thermalization; to pose and examine the needs for and benefits of cold moderators for neutron scattering and other applications of pulsed neutron sources; to summarize experience with pulsed source, cold moderators, their performance, effectiveness, successes, problems and solutions, and the needs for operational data; to compile and evaluate new ideas for cold moderator materials and geometries; to review methods of measuring and characterizing pulsed source cold moderator performance; to appraise methods of calculating needed source characteristics and to evaluate the needs and prospects for improvements; to assess the state of knowledge of data needed for calculating the neutronic and engineering performance of cold moderators; and to outline the needs for facilities for testing various aspects of pulsed source cold moderator performance.
Date: January 6, 1999
Creator: Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Cold moderators for pulsed neutron sources

Description: This paper reviews cold moderators in pulsed neutron sources and provides details of the performance of different cold moderator materials and configurations. Analytical forms are presented which describe wavelength spectra and emission time distributions. Several types of cooling arrangements used in pulsed source moderators are described. Choices of materials are surveyed. The author examines some of the radiation damage effects in cold moderators, including the phenomenon of burping'' in irradiated cold solid methane. 9 refs., 15 figs., 4 tabs.
Date: January 1, 1990
Creator: Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Some concluding remarks about cold moderator development

Description: This paper is the transcription of remarks made at the conclusion of the Workshop on Cold Neutron Sources held at the Los Angeles National Laboratory, Los Alamos, New Mexico, March 5--7, 1990. Areas of interest include the following: scattering functions; cold moderator materials; radiation mixing of chemical composition; comparison of some pulsed moderator spectra; hydrogen mixtures; premoderators and shields; composite reflectors; exotic moderator materials; deuterated methanes; mixed moderator materials; and test facility availabilities. 2 refs., 4 figs., 1 tab. (MHB)
Date: January 1, 1990
Creator: Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Design study of a time of flight small-angle diffractometer for a pulsed neutron source

Description: The design study for a neutron SAS instrument at Argonne's proposed Intense Pulsed Neutron Source (peak thermal neutron flux 10/sup 16/ n/cm/sup 2/-sec) indicates that an effective high-resolution TOF SAS diffractometer can be constructed. The design features include a converging slit collimator, provision for 5 x 5 cm/sup 2/ sample cross sectional area, and a 1 x 1 m/sup 2/, two-dimensional detector. The fractional wavelength resolution of the instrument is negligibly small for all wavelengths. The resolution was computed by Monte Carlo simulation and is constant over most of the Q range. A special feature of the instrument is the wide range of accessible Q's, without the requirement of instrument configurational changes. The flux on sample exceeds that at conventional reactor instruments of comparable resolution.
Date: January 1, 1977
Creator: Carpenter, J.M. & Faber, J. Jr.
Partner: UNT Libraries Government Documents Department

Examination of disks from the IPNS depleted uranium target

Description: This report describes the results of examining the Zircaloy-2 clad depleted uranium disks from the Intense Pulse Neutron Source (IPNS) Target. That target operated from August, 1981 to June, 1988 and from September, 1991 to September, 1992 at 450 MeV, pulsing at 30 Hz with a time average proton current of about 15 {micro}A. The target was removed from service when the presence of fission products ({sup 135}Xe) in the coolant cover gas indicated a failure in the Zircaloy-2 cladding. Altogether, the target had absorbed about 240 mA hours of proton current, and endured between 50,000 and 100,000 thermal cycles. The purpose of the examination was to assess the condition of the disks and determine the cause of the cladding failure. The results of visual, gamma ray scanning, and destructive metallurgical examination of two disks are described.
Date: October 1, 1995
Creator: Strain, R.V. & Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Heat generation and neutron beam characteristics in a high power pulsed spallation neutron source

Description: In the course of conceptual design of a high power pulsed spallation source, a Monte Carlo model was developed for heat generation and neutronics studies. In this paper, we present two sets of results. The first set of calculations was performed with a simple target model to investigate general characteristics of power distribution and neutron production with various proton energies ranging from 0.8 to 12 GeV. The second set was performed with a realistic target model including major components of the target system to provide basic parameters for engineering design of a high power pulsed spallation source. Calculated results generally confirm that higher proton energy provides and advantage in target cooling system requirements and yet somewhat lower neutron beam intensity as a counter effect. The heat generation in the systems surrounding the target was investigated in detail and found to have important variation with position and according to proton beam energy. Calculations of the neutron currents from the moderators showed that the neutron beam intensity from moderators in the front region of the target decreased fro higher proton energy while that from moderators in the back region of the target remained almost unchanged.
Date: November 1, 1996
Creator: Jerng, D.W. & Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Neutron science opportunities at pulsed spallation neutron sources

Description: Using the IPNS Upgrade plan developed at Argonne National Laboratory as a worked example of the design of a pulsed spallation neutron source, this paper explores some of the scientific applications of an advanced facility for materials science studies and the instrumentation for those purposes.
Date: December 31, 1996
Creator: Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Measurement and fitting of spectrum and pulse shapes of a liquid methane moderator at IPNS

Description: We have measured the absolute intensity, and the energy spectrum, and the pulse shapes as function of neutron energy for the IPNS liquid CH/sub 4/ F moderator, at 108 K. We have fitted the spectrum, corrected for attenuation by aluminum in the beam, using a new cutoff function and fitted the pulse shapes to a new function which is the sum of two decaying exponentials, convoluted with a gaussian, and determined the wavelength variation of the parameters. We present here the results of a preliminary analysis.
Date: January 1, 1983
Creator: Carpenter, J.M.; Robinson, R.A. & Taylor, A.D.
Partner: UNT Libraries Government Documents Department

Slow neutron leakage spectra from spallation neutron sources

Description: An efficient technique is described for Monte Carlo simulation of neutron beam spectra from target-moderator-reflector assemblies typical of pulsed spallation neutron sources. The technique involves the scoring of the transport-theoretical probability that a neutron will emerge from the moderator surface in the direction of interest, at each collision. An angle-biasing probability is also introduced which further enhances efficiency in simple problems. These modifications were introduced into the VIM low energy neutron transport code, representing the spatial and energy distributions of the source neutrons approximately as those of evaporation neutrons generated through the spallation process by protons of various energies. The intensity of slow neutrons leaking from various reflected moderators was studied for various neutron source arrangements. These include computations relating to early measurements on a mockup-assembly, a brief survey of moderator materials and sizes, and a survey of the effects of varying source and moderator configurations with a practical, liquid metal cooled uranium source Wing and slab, i.e., tangential and radial moderator arrangements, and Be vs CH/sub 2/ reflectors are compared. Results are also presented for several complicated geometries which more closely represent realistic arrangements for a practical source, and for a subcritical fission multiplier such as might be driven by an electron linac. An adaptation of the code was developed to enable time dependent calculations, and investigated the effects of the reflector, decoupling and void liner materials on the pulse shape.
Date: February 1, 1980
Creator: Das, S.G.; Carpenter, J.M. & Prael, R.E.
Partner: UNT Libraries Government Documents Department

Measurement and fitting of pulse shapes of moderators at IPNS (Intense Pulsed Neutron Source): Progress report

Description: We present a progress report on measurements and fitting of pulse shapes for neutrons emerging from one solid and two liquid methane moderators in IPNS. A time-focused crystal spectrometer arrangement was used with a cooled Ge monochromator. Data analysis of one of the liquid methane moderators has shown the need for some generalization of the Ikeda-Carpenter function that worked well for fitting pulse shapes of polyethylene moderators. We describe attempts to model physical insight into the wavelength dependence of function parameters. 5 refs., 7 figs.
Date: January 1, 1988
Creator: Bywater, R.L. Jr.; Williams, R.E. & Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Enriched vs non-enriched vs non-fissile targets for pulsed spallation neutron sources

Description: Numerous options exist among alternatives for target material and design of the neutron producing target in pulsed spallation neutron sources. This report surveys the advantages, disadvantages and limitations of some of the alternatives, including discussions of neutron yields, delayed neutron backgrounds, source pulse widths, source-to-moderator coupling, materials performance, fabrication problems, safeguards and security and hazards questions. 5 refs., 5 figs., 2 tabs.
Date: January 1, 1990
Creator: Carpenter, J.M.
Partner: UNT Libraries Government Documents Department

Miniature Neutron Sources: Thermal Neutron Sources and Their Users in the Academic Field

Description: The three levels of thermal neutron sources are introduced - University laboratory sources infrastructure sources and world-class sources - and the needs for each kind and their inter-dependence will be emphasized. A description of the possibilities for University sources based on {alpha}-Be reactions or spontaneous fission emission is given, and current experience with them is described. A new generation of infrastructure sources is needed to continue the regional programs based on small reactors. Some possibilities for accelerator sources that could meet this need are considered.
Date: January 1, 1992
Creator: Egelstaff, P. A. & Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Deterioration of performance of neutron moderators under intense irradiation

Description: In pulsed neutron sources, fixed moderators such as polyethylene and solid methane slow down fast (MeV) neutrons from the primary source to energies of use for spectroscopy (less than or equal to10 eV). Radiation-induced changes in their composition alter their spectral and pulse characteristics. We report the results of fitting time-average spectra from polyethylene and solid methane moderators in Argonne's Intense Pulsed Neutron Source as a function of total fast-neutron radiation dose. The thermal-to-epithermal flux ratio varies most significantly, while the Maxwellian energy and the parameters describing the epithermal component change only slightly. We have used modified forms of Westcott's joining function for this purpose. We provide an integral of the spectrum that is useful for determining the delayed neutron background.
Date: January 1, 1986
Creator: Carpenter, J.M.; Cudrnak, S.S. & DeCusatis, C.M.
Partner: UNT Libraries Government Documents Department

The development of solid methane neutron moderators at the Intense Pulsed Neutron Source facility of Argonne National Laboratory.

Description: The Intense Pulsed Neutron Source (IPNS) started using solid methane moderators in 1985 because of their efficient conversion (about 3.5 times greater than was achieved with a liquid hydrogen moderator) of fast neutrons to long wavelength neutrons. However, the solid methane moderators experienced numerous failures due to pressure surges caused by a combination of (1) the release of stored energy, which occurred when methane radiolytic products recombined, and (2) the expansion of hydrogen, which built up in the solid methane during irradiation. During the ensuing years studies were made to determine how to operate the solid methane moderators without causing failure. The rate at which stored energy built up during irradiation and the temperature at which hydrogen was released during annealing were determined. Since 1993 IPNS has successfully operated the solid methane moderators (at about 30 K) by periodically annealing to the liquid state around 90 K after every roughly three days of irradiation.
Date: March 10, 1999
Creator: Carpenter, J. M.; Miller, M. E. & Scott, T. L.
Partner: UNT Libraries Government Documents Department

Neutronics studies for a long-wavelength target station at SNS.

Description: The Spallation Neutron Source (SNS), under construction at Oak Ridge National Laboratory, will be the premier facility for neutron scattering studies in the United States. From the outset the SNS can achieve additional flexibility and accommodate a broader range of scientific investigation than would be possible with only the High Power Target Station by utilizing two target stations, each operating under a separate set of conditions and optimized for a certain class of instruments. A second target station, termed the Long-Wavelength Target Station (LWTS), would operate at a lower pulse rate (e.g., 10 vs. 60 Hz) and utilize very cold moderators to emphasize low-energy (long wavelength) neutrons. The LWTS concept discussed here obtains the highest low-energy fluxes possible for neutron scattering instruments by using a heavy-water-cooled solid tungsten target with two moderators in slab geometry and one in a front wing position. The primary focus has been on solid methane moderators, with liquid methane and hydrogen also considered. We used MCNPX to conduct a series of optimization and sensitivity studies to help determine the optimal neutronic parameters of the LWTS. We compared different options based on the thermal and epithermal fluxes as determined by fitting the spectral intensity of the moderators with a Maxwellian peak and a modified Westcott function. The primary parameters are the moderator positions and composition and the target size. We report results for spectral intensity, pulse shapes, high-energy neutron emission, heating profiles in the target, and target activation.
Date: September 21, 2001
Creator: Micklich, B. J.; Iverson, E. B. & Carpenter, J. M.
Partner: UNT Libraries Government Documents Department

Slow Neutron Leakage Spectra from Spallation Neutron Sources

Description: An efficient technique is described for Monte Carlo simulation of neutron beam spectra from target-moderator-reflector assemblies typical of pulsed spallation neutron sources. The technique involves the scoring of the transport-theoretical probability that a neutron will emerge from the moderator surface in the direction of interest, at each collision. An angle-biasing probability is also introduced which further enhances efficiency in simple problems.
Date: February 1980
Creator: Das, Shashikala G.; Carpenter, J. M. & Prael, R. E.
Partner: UNT Libraries Government Documents Department