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Title: Prompt Neutron Decay Constant Measurements on a Polyethylene-Reflected Sphere of HEU

Authors:
ORCiD logo [1];  [1]; ORCiD logo [1]
  1. Los Alamos National Laboratory
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1418746
Report Number(s):
LA-UR-18-20497
DOE Contract Number:
AC52-06NA25396
Resource Type:
Conference
Resource Relation:
Conference: ANS Winter 2017 ; 2017-10-29 - 2017-10-29 ; Washington DC, District Of Columbia, United States
Country of Publication:
United States
Language:
English
Subject:
Rossi Alpha, Prompt Neutron Decay Constants, HEU

Citation Formats

McKenzie, George Espy IV, Hutchinson, Jesson D., and Myers, William L. Prompt Neutron Decay Constant Measurements on a Polyethylene-Reflected Sphere of HEU. United States: N. p., 2018. Web.
McKenzie, George Espy IV, Hutchinson, Jesson D., & Myers, William L. Prompt Neutron Decay Constant Measurements on a Polyethylene-Reflected Sphere of HEU. United States.
McKenzie, George Espy IV, Hutchinson, Jesson D., and Myers, William L. 2018. "Prompt Neutron Decay Constant Measurements on a Polyethylene-Reflected Sphere of HEU". United States. doi:. https://www.osti.gov/servlets/purl/1418746.
@article{osti_1418746,
title = {Prompt Neutron Decay Constant Measurements on a Polyethylene-Reflected Sphere of HEU},
author = {McKenzie, George Espy IV and Hutchinson, Jesson D. and Myers, William L.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2018,
month = 1
}

Conference:
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  • Numerous benchmark measurements have been performed to enable developers of neutron transport models and codes to evaluate the accuracy of their calculations. In particular, for criticality safety applications, the International Criticality Safety Benchmark Experiment Program (ICSBEP) annually publishes a handbook of critical and subcritical benchmarks. Relatively fewer benchmark measurements have been performed to validate photon transport models and codes, and unlike the ICSBEP, there is no program dedicated to the evaluation and publication of photon benchmarks. Even fewer coupled neutron-photon benchmarks have been performed. This report documents a coupled neutron-photon benchmark for plutonium metal reflected by polyethylene. A 4.5-kg spheremore » of ?-phase, weapons-grade plutonium metal was measured in six reflected configurations: (1) Bare; (2) Reflected by 0.5 inch of high density polyethylene (HDPE); (3) Reflected by 1.0 inch of HDPE; (4) Reflected by 1.5 inches of HDPE; (5) Reflected by 3.0 inches of HDPE; and (6) Reflected by 6.0 inches of HDPE. Neutron and photon emissions from the plutonium sphere were measured using three instruments: (1) A gross neutron counter; (2) A neutron multiplicity counter; and (3) A high-resolution gamma spectrometer. This report documents the experimental conditions and results in detail sufficient to permit developers of radiation transport models and codes to construct models of the experiments and to compare their calculations to the measurements. All of the data acquired during this series of experiments are available upon request.« less
  • Prompt neutron decay constants were measured for a delayed critical, unmoderated and unreflected U metal sphere at the Oak Ridge Critical Experiments Facility. Prompt neutron decay constant was 1.1095{+-}0.0013 {mu}s{sup -1}. This can be used to verify calculational methods, both deterministic and Monte Carlo neutron transport methods. This value is in agreement with the value from GODIVA I data corrected for effects of support structure (1.10{+-}0.01 {mu}s{sup -1}) but has a much smaller error as a result of the large number (167) of the measurements here and the high degree of sphericity of the sphere.
  • The use of fast-response liquid scintillators for passive measurements with highly enriched uranium (HEU) castings provides information on the timescale of the fission chain multiplication process for HEU. Thus, these detectors produce time responses characteristic of the HEU and not the moderator around 3He counters. Up to five HEU castings were assembled and the passive time coincidence measurements performed. The prompt neutron decay constants inferred from the Feynman variance data with the arrays of large liquid scintillators are compared with decay constants obtained from previously presented Feynman variance data collected in active interrogation measurements with these same HEU castings. Themore » active measurements used plastic scintillation detectors adjacent to the castings to eliminate time-of-flight effects and showed that the prompt neutron decay constant is clearly not exponential. However, time-of-flight effects in the passive measurements result in exponential behavior and allow the Feynman variance data to be fit with the well-known point kinetics analytical formula. The characterization of the prompt neutron decay constant is investigated by comparing the results of the passive and active measurement data.« less