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Title: A priori precision estimation for neutron triples counting

Abstract

The nondestructive assay of Plutonium bearing items for criticality, safety, security, safeguards, inventory balance, process control, waste management and compliance is often undertaken using correlated neutron counting. In particular Multiplicity Shift Register analysis allows one to extract autocorrelation parameters from the pulse train which can, within the framework of a simple interpretational model, be related to the effective {sup 240}Pu spontaneous fission mass present. The effective {sup 240}Pu mass is a weighted sum of the {sup 238}Pu, {sup 240}Pu and {sup 242}Pu masses so if the relative isotopic composition of the Pu can be established from the measured {sup 240}Pu effective mass one can estimate the total Pu mass and also the masses of the individual isotopes, example the fissile species {sup 239}Pu and {sup 241}Pu. In multiplicity counting three counting rates are obtained. These are the Singles, Doubles and Triples rates. The Singles rate is just the gross, totals or trigger rate. The Doubles and Triples rates are calculated from factorial moments of the observed signal triggered neutron multiplicity distributions following spontaneous fission in the item and can be thought of as the rate of observed coincident pairs and coincident triplets on the pulse train. Coincident events come aboutmore » because the spontaneous fission and induced fission chains taking place in the item result in bursts of neutrons. These remain time correlated during the detection process and so retain information, through the burst size distribution, about the Pu content. In designing and assessing the performance of a detector system to meet a given goal it is necessary to make a priori estimates of the counting precision for all three kinds of rates. This is non-trivial because the counting does not obey the familiar rules of a Poissonian counting experiment because the pulse train has time correlated events on it and the train is sampled by event triggered gates that may overlap. For Singles and Doubles simple approximate analytical empirical rules for how to estimate the variance have been developed guided by theory and refined by experiment. However, for Triples no equivalent rules have been put forward and tested until now. In this work we propose an analytical expression, the CSH relation, for the variance on the Triples count and exercise it against experimental data gathered for Pu items measured in the Los Alamos National Laboratory's Epithermal Neutron Multiplicity Counter (ENMC). Preliminary results are encouraging and reasonable agreement with observation, considered fit for scoping studies, is obtained. We have also looked at the behavior using Monte Carlo simulations. (authors)« less

Authors:
; ;  [1]
  1. Safeguards Science and Technology Group N-1, Nuclear Nonproliferation Div., Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
Publication Date:
OSTI Identifier:
22039808
Resource Type:
Conference
Resource Relation:
Conference: ANIMMA 2011: 2. International Conference on Advancements in Nuclear Instrumentation, Measurement Methods and their Applications, Ghent (Belgium), 6-9 Jun 2011; Other Information: Country of input: France; 25 refs.; IEEE Catalog Number: CFP1124I-CDR
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ACCURACY; COINCIDENCE METHODS; COMPUTERIZED SIMULATION; COUNTING RATES; EFFECTIVE MASS; ELECTRON MULTIPLIERS; EPITHERMAL NEUTRONS; EXPERIMENTAL DATA; ISOTOPE RATIO; LANL; MONTE CARLO METHOD; NEUTRON DETECTORS; PLUTONIUM 238; PLUTONIUM 239; PLUTONIUM 240; PLUTONIUM 241; PLUTONIUM 242; RADIOACTIVE WASTE MANAGEMENT; SECURITY; SPONTANEOUS FISSION

Citation Formats

Croft, S, Swinhoe, M T, and Henzl, V. A priori precision estimation for neutron triples counting. United States: N. p., 2011. Web. doi:10.1109/ANIMMA.2011.6172923.
Croft, S, Swinhoe, M T, & Henzl, V. A priori precision estimation for neutron triples counting. United States. doi:10.1109/ANIMMA.2011.6172923.
Croft, S, Swinhoe, M T, and Henzl, V. Fri . "A priori precision estimation for neutron triples counting". United States. doi:10.1109/ANIMMA.2011.6172923.
@article{osti_22039808,
title = {A priori precision estimation for neutron triples counting},
author = {Croft, S and Swinhoe, M T and Henzl, V},
abstractNote = {The nondestructive assay of Plutonium bearing items for criticality, safety, security, safeguards, inventory balance, process control, waste management and compliance is often undertaken using correlated neutron counting. In particular Multiplicity Shift Register analysis allows one to extract autocorrelation parameters from the pulse train which can, within the framework of a simple interpretational model, be related to the effective {sup 240}Pu spontaneous fission mass present. The effective {sup 240}Pu mass is a weighted sum of the {sup 238}Pu, {sup 240}Pu and {sup 242}Pu masses so if the relative isotopic composition of the Pu can be established from the measured {sup 240}Pu effective mass one can estimate the total Pu mass and also the masses of the individual isotopes, example the fissile species {sup 239}Pu and {sup 241}Pu. In multiplicity counting three counting rates are obtained. These are the Singles, Doubles and Triples rates. The Singles rate is just the gross, totals or trigger rate. The Doubles and Triples rates are calculated from factorial moments of the observed signal triggered neutron multiplicity distributions following spontaneous fission in the item and can be thought of as the rate of observed coincident pairs and coincident triplets on the pulse train. Coincident events come about because the spontaneous fission and induced fission chains taking place in the item result in bursts of neutrons. These remain time correlated during the detection process and so retain information, through the burst size distribution, about the Pu content. In designing and assessing the performance of a detector system to meet a given goal it is necessary to make a priori estimates of the counting precision for all three kinds of rates. This is non-trivial because the counting does not obey the familiar rules of a Poissonian counting experiment because the pulse train has time correlated events on it and the train is sampled by event triggered gates that may overlap. For Singles and Doubles simple approximate analytical empirical rules for how to estimate the variance have been developed guided by theory and refined by experiment. However, for Triples no equivalent rules have been put forward and tested until now. In this work we propose an analytical expression, the CSH relation, for the variance on the Triples count and exercise it against experimental data gathered for Pu items measured in the Los Alamos National Laboratory's Epithermal Neutron Multiplicity Counter (ENMC). Preliminary results are encouraging and reasonable agreement with observation, considered fit for scoping studies, is obtained. We have also looked at the behavior using Monte Carlo simulations. (authors)},
doi = {10.1109/ANIMMA.2011.6172923},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2011},
month = {7}
}

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