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Title: Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector

Abstract

Abstract not provided.

Authors:
; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1429798
Report Number(s):
SAND-2017-6863J
654892
DOE Contract Number:
AC04-94AL85000
Resource Type:
Program Document
Resource Relation:
Journal Name: Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector
Country of Publication:
United States
Language:
English

Citation Formats

Walsh, David S., Crowder, Stephen V., and Walsh, David S. Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector. United States: N. p., 2017. Web.
Walsh, David S., Crowder, Stephen V., & Walsh, David S. Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector. United States.
Walsh, David S., Crowder, Stephen V., and Walsh, David S. Thu . "Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector". United States. doi:.
@article{osti_1429798,
title = {Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector},
author = {Walsh, David S. and Crowder, Stephen V. and Walsh, David S.},
abstractNote = {Abstract not provided.},
doi = {},
journal = {Estimating Uncertainty in Laboratory Neutron Measurements Made with a Lead Probe Scaler Detector},
number = ,
volume = ,
place = {United States},
year = {Thu Jun 01 00:00:00 EDT 2017},
month = {Thu Jun 01 00:00:00 EDT 2017}
}

Program Document:
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  • The sources of uncertainty in the loss-of-fluid test (LOFT) self-powered neutron detector (SPND) are analyzed, and recommendations for reducing the measurement uncertainty are given.
  • The lead probe neutron detector was originally designed by Spencer and Jacobs in 1965. The detector is based on lead activation due to the following neutron scattering reactions: {sup 207}Pb(n, n'){sup 207m}Pb and {sup 208}Pb(n, 2n){sup 207m}Pb. Delayed gammas from the metastable state of {sup 207m}Pb are counted using a plastic scintillator. The half-life of {sup 207m}Pb is 0.8 seconds. In the work reported here, MCNP was used to optimize the efficiency of the lead probe by suitably modifying the original geometry. A prototype detector was then built and tested. A 'layer cake' design was investigated in which thin (<more » 5 mm) layers of lead were sandwiched between thicker ({approx} 1 - 2 cm) layers of scintillator. An optimized 'layer cake' design had Figures of Merit (derived from the code) which were a factor of 3 greater than the original lead probe for DD neutrons, and a factor of 4 greater for DT neutrons, while containing 30% less lead. A smaller scale, 'proof of principle' prototype was built by Bechtel/Nevada to verify the code results. Its response to DD neutrons was measured using the DD dense plasma focus at Texas A&M and it conformed to the predicted performance. A voltage and discriminator sweep was performed to determine optimum sensitivity settings. It was determined that a calibration operating point could be obtained using a {sup 133}Ba 'bolt' as is the case with the original lead probe.« less
  • Sandia National Laboratories' facilities for development testing of neutron tubes and generators utilize waveform digitizers which are computer-controlled through an industry standard computer interface. This manual describes a computer-controlled scaler/integrator neutron measurement chassis which is interface compatible. The chassis has scintillation-counting and integrator circuitry designed to work with two types of neutron probes, one that monitors 14-MeV neutrons from the DT reaction and another that monitors 2.5-MeV neutrons from the DD reaction. 6 refs., 8 figs., 1 tab.
  • Measurements of neutron fluctuations have been made on a lattice of slightly enriched UO/sub 2/ fuel rods in light water. A /sup 99/Mo activation measurement provided the absolute efficiencies of the three neutron counting channels employed. Fluctuations are found to be substantially larger than predicted by a simple model ignoring spatial effects and delayed neutrons. Large reactivity changes were monitored by changes in degree of fluctuations. The effects of large counting losses on the measured dispersion parameter, Y, were determined. The natural neutron source strength in the reactor was measured to be 1.53 +- 0.15 neutrons per second per kgmmore » of U. (NSA 23: 2107)« less