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Title: Use of MCNPX for Alpha Spectrometry Simulations of a Continuous Air Monitor

Abstract

The purpose of this study was to determine if the alpha energy spectrum in a Passive Implanted Planar Silicon (PIPS) detector, as modeled by MCNPX [1], can be used to design a radon stripping algorithm for a continuous air monitor (CAM). This stripping algorithm would be employed to discriminate naturally occurring radioisotopes from the anthropogenic for nuclear safety -related applications. It is hoped that using an algorithm based on MCNPX simulations, the CAM will not be prone to false alarms when radon levels are dynamic as identified in other CAM systems [2,3]. This work is focused on the design of the next generation air particulate detector (NGAPD) for the United States Navy. The primary isotope of interest is Co-60. This radionuclide emits a beta with an average energy of 96 keV. Therefore, once deposited on the CAM filter, it will produce a beta continuum seen by the PIPS detector. In addition, as radon progeny is deposited on the air filter, these will give rise to characteristic alpha peaks and a beta continuum. This is primarily an issue in port-or land-based applications. Ultimately, measurement of a radon alpha spectrum is desired to predict the amount of beta activity which would bemore » measured from the radon progeny decay chains. All excess beta activity could then be attributed to anthropogenic sources once the radon progeny contributions have been stripped out.« less

Authors:
Publication Date:
Research Org.:
National Security Technologies, LLC
Sponsoring Org.:
USDOE National Nuclear Security Administration (NA)
OSTI Identifier:
946313
Report Number(s):
DOE/NV/25946-106
Journal ID: 0003-018X; TRN: US200903%%366
DOE Contract Number:
DE-AC52-06NA25946
Resource Type:
Conference
Resource Relation:
Journal Name: Transactions of the American Nuclear Society; Journal Volume: 96; Conference: American Nuclear Society Annual Meeting; Boston, MA; June 24-28, 2007
Country of Publication:
United States
Language:
English
Subject:
47 OTHER INSTRUMENTATION; AIR FILTERS; ALGORITHMS; ALPHA SPECTROSCOPY; DECAY; DESIGN; MONITORS; PARTICULATES; PROGENY; RADIOISOTOPES; RADON; SILICON; Alpha Spectrometry, Continuous Air Monitor, United States Navy

Citation Formats

Robert Hayes, Craig Marianno. Use of MCNPX for Alpha Spectrometry Simulations of a Continuous Air Monitor. United States: N. p., 2007. Web.
Robert Hayes, Craig Marianno. Use of MCNPX for Alpha Spectrometry Simulations of a Continuous Air Monitor. United States.
Robert Hayes, Craig Marianno. Mon . "Use of MCNPX for Alpha Spectrometry Simulations of a Continuous Air Monitor". United States. doi:. https://www.osti.gov/servlets/purl/946313.
@article{osti_946313,
title = {Use of MCNPX for Alpha Spectrometry Simulations of a Continuous Air Monitor},
author = {Robert Hayes, Craig Marianno},
abstractNote = {The purpose of this study was to determine if the alpha energy spectrum in a Passive Implanted Planar Silicon (PIPS) detector, as modeled by MCNPX [1], can be used to design a radon stripping algorithm for a continuous air monitor (CAM). This stripping algorithm would be employed to discriminate naturally occurring radioisotopes from the anthropogenic for nuclear safety -related applications. It is hoped that using an algorithm based on MCNPX simulations, the CAM will not be prone to false alarms when radon levels are dynamic as identified in other CAM systems [2,3]. This work is focused on the design of the next generation air particulate detector (NGAPD) for the United States Navy. The primary isotope of interest is Co-60. This radionuclide emits a beta with an average energy of 96 keV. Therefore, once deposited on the CAM filter, it will produce a beta continuum seen by the PIPS detector. In addition, as radon progeny is deposited on the air filter, these will give rise to characteristic alpha peaks and a beta continuum. This is primarily an issue in port-or land-based applications. Ultimately, measurement of a radon alpha spectrum is desired to predict the amount of beta activity which would be measured from the radon progeny decay chains. All excess beta activity could then be attributed to anthropogenic sources once the radon progeny contributions have been stripped out.},
doi = {},
journal = {Transactions of the American Nuclear Society},
number = ,
volume = 96,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • The presence of radon and thoron daughters causes interference in the plutonium channel of alpha continuous air monitors used to detect airborne plutonium. Single-channel alpha energy spectroscopy is used to minimize this effect, and additional compensation is provided by electronically subtracting a constant fraction of the count rate appearing in the higher energy radon window'' from the count rate appearing in the plutonium window. The standard deviation of the resulting net count rate is nonzero. The probability of falsely reporting the presence of plutonium when in fact none is present (Type I error) is influenced by this nonzero standard deviationmore » and becomes unacceptably high if the alarm setpoint is too low. These conditions were used to simulate the response of an alpha continuous air monitors to radon interference using a Monte Carlo simulation. Radon and thoron daughter concentrations measured during a one-week period were used. These measurements indicated the diurnal variations of over two decades in radon and thoron daughter response as well as a longer in-growth of {sup 212}Pb and subsequent daughter transitions were present. The response of the logarithmic count rate meter was also simulated to preserve the normally observed fluctuations. The simulations include response of the alpha CAM with the observed radon and thoron daughter contributions with and without plutonium present. Information obtained included the following as a function of alarm setpoint: number of Type I alarms and the time required to provide a true alarm after initiation of simulated plutonium releases. 3 refs., 8 figs., 1 tab.« less
  • A new alpha Continuous Air Monitor (CAM) sampler is being developed for use in detecting the presence of alpha-emitting aerosol particles. The effort involves design, fabrication and evaluation of systems for the collection of aerosol and for the processing of data to speciate and quantify the alpha emitters of interest. At the present time we have a prototype of the aerosol sampling system and we have performed wind tunnel tests to characterize the performance of the device for different particle sizes, wind speeds, flow rates and internal design parameters. The results presented herein deal with the aerosol sampling aspects ofmore » the new CAM sampler. Work on the data processing, display and alarm functions is being done in parallel with the particle sampling work and will be reported separately at a later date. 17 refs., 5 figs., 3 tabs.« less
  • Monitoring requirements for airborne plutonium are becoming increasingly stringent as regulations require progressively lower limits of detection. The current requirement of 8 DAC-hours reflects the limitations of today's technology for workplace monitoring. Simultaneously, closed-ventilation systems and massive concrete buildings are concentrating radon and its daughter products. The daughter products produce a spectrum that degrades the ability of a continuous air monitor (CAM) to make accurate low-level determinations of plutonium. Los Alamos has been working on improved methods for detecting airborne alpha emitters in the presence of radon daughter products for the last 2 years. These efforts were recently coordinated intomore » a program to examine all facets of CAM operation including aerosol collection, detection, signal processing, computation, alarming, communications, and finally, instrument cost. 4 refs., 2 figs.« less
  • Continuous air monitoring instruments (CAMS) deployed in laboratories in the TA-55 plutonium facility at Los Alamos National Laboratory (LANL) alarmed less than 33 percent of the time when fixed air sample measurements in the same laboratory showed integrated concentrations exceeding 500 DAC-hrs. The purpose of this study was to explore effects of non-instrument variables on alarm sensitivities for properly working CAMS. Non-instrument variables include air flow patterns, particle size of released material, and the energy of the release. Dilution Factors (DFs) for 21 airborne releases in various rooms and of different magnitudes were calculated and compared. The median DF formore » releases where the CAM alarmed was 13.1 while the median DF for releases where the CAM did not alarm was 179. Particle sizes ranged considerably with many particles larger than 10 {mu}m. The cause of the release was found to be important in predicting if a CAM would alarm with releases from bagouts resulting in the greatest percentage of CAM alarms. The results of this study suggest that a two-component strategy for CAM placement at LANL be utilized. The first component would require CAMs at exhaust points in the rooms to provide for reliable detection for random release locations. The second component would require placing CAMs at locations where releases have historically been seen. Finally, improvements in CAM instrumentation is needed.« less