Neutron Multiplicity for Neutron Induced Fission of 235U, 238U, and 239Pu as a Function of Neutron Energy

Neutron Multiplicity for Neutron Induced Fission of 235U, 238U, and 239Pu as a Function of Neutron Energy
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Release: 1986
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Recent development in the theory and practice of neutron correlation (''coincidence'') counting require knowledge of the higher factorial moments of the P/sub .nu./ distribution (the probability that (.nu.) neutrons are emitted in a fission) for the case where the fission is induced by bombarding neutrons of more than thermal energies. In contrast to the situation with spontaneous and thermal neutron induced fission, where with a few exceptions the P/sub .nu./ is reasonably well known, in the fast neutron energy region, almost no information is available concerning the multiplicity beyond the average value, (.nu.), even for the most important nuclides. The reason for this is the difficulty of such experiments, with consequent statistically poor and physically inconsistent results.

Basic Physics Data

Basic Physics Data
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Total Pages: 32
Release: 2015
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From October 1 to October 17 a team of researchers from UM visited the LANSCE facility for an experiment during beam-time allotted from October 4 to October 17. A total of 24 detectors were used at LANSCE including liquid organic scintillation detectors (EJ-309), NaI scintillation detectors, and Li-6 enriched glass detectors. It is a double time-offlight (TOF) measurement using spallation neutrons generated by a target bombarded with pulsed high-energy protons. The neutrons travel to an LLNL-manufactured parallel plate avalanche chamber (PPAC) loaded with thin U-235 foils in which fission events are induced. The generated fission neutrons and photons are then detected in a detector array designed and built at UM and shipped to LANSCE. Preparations were made at UM, where setup and proposed detectors were tested. The UM equipment was then shipped to LANSCE for use at the 15L beam of the weapons neutron research (WNR) facility.

Measurement of the Average Multiplicity Prompt-fission-neutrons from [238]u(n, F) and [235]u(n, F) from 0.7 to 200 MeV.

Measurement of the Average Multiplicity Prompt-fission-neutrons from [238]u(n, F) and [235]u(n, F) from 0.7 to 200 MeV.
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Total Pages: 5
Release: 2004
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Prompt-fission-neutron multiplicities were measured at a 'white' neutron source for the fission of 238U and 235U up to 200 MeV. The data are of great importance in the connection of accelerator-coupled nuclear reactor systems incinerating actinides, with uranium considered as a prototype actinide. We report that the fission induced by 200 MeV neutrons produces (almost equal to)10 more prompt neutrons than the fission induced by reactor neutrons. In conclusion, new data on {bar {nu}}{sub p} are reported with errors {

Measurements of the Neutron-induced Fission Cross Sections of 24°Pu and 242Pu Relative to 235U. [0. 02 to 30 MeV, Tables].

Measurements of the Neutron-induced Fission Cross Sections of 24°Pu and 242Pu Relative to 235U. [0. 02 to 30 MeV, Tables].
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Release: 1976
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A continuation is given of the fission-cross-section ratio measurements in progress at the Lawrence Livermore Laboratory. Preliminary results are provided for the 24°Pu/235U and 242Pu/235U ratios from 0.02 to 30 MeV and 0.1 to 30 MeV, respectively. Using the threshold-cross-section method, the ratios were normalized to the values 1.368 +- 0.030 and 1.116 +- 0.025, respectively, from 1.75 to 4.00 MeV.

An Analysis Technique for Active Neutron Multiplicity Measurements Based on First Principles

An Analysis Technique for Active Neutron Multiplicity Measurements Based on First Principles
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Release: 2012
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Passive neutron multiplicity counting is commonly used to quantify the total mass of plutonium in a sample, without prior knowledge of the sample geometry. However, passive neutron counting is less applicable to uranium measurements due to the low spontaneous fission rates of uranium. Active neutron multiplicity measurements are therefore used to determine the 235U mass in a sample. Unfortunately, there are still additional challenges to overcome for uranium measurements, such as the coupling of the active source and the uranium sample. Techniques, such as the coupling method, have been developed to help reduce the dependence of calibration curves for active measurements on uranium samples; although, they still require similar geometry known standards. An advanced active neutron multiplicity measurement method is being developed by Texas A & M University, in collaboration with Los Alamos National Laboratory (LANL) in an attempt to overcome the calibration curve requirements. This method can be used to quantify the 235U mass in a sample containing uranium without using calibration curves. Furthermore, this method is based on existing detectors and nondestructive assay (NDA) systems, such as the LANL Epithermal Neutron Multiplicity Counter (ENMC). This method uses an inexpensive boron carbide liner to shield the uranium sample from thermal and epithermal neutrons while allowing fast neutrons to reach the sample. Due to the relatively low and constant fission and absorption energy dependent cross-sections at high neutron energies for uranium isotopes, fast neutrons can penetrate the sample without significant attenuation. Fast neutron interrogation therefore creates a homogeneous fission rate in the sample, allowing for first principle methods to be used to determine the 235U mass in the sample. This paper discusses the measurement method concept and development, including measurements and simulations performed to date, as well as the potential limitations.