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Title: Minimum detectable activity and false alarm rate relationships for alpha continuous air monitors

Abstract

The U.S. Department of Energy rule for Occupational Radiation Protection (10 CFR Part 835, December 1993) and the DOE Radiological Control Manual (the RCM) (DOE/EH-0256T, Rev. 1, April 1994) require the use of continuous air monitors (CAMs) in normally occupied areas where an individual is likely to be exposed to a concentration of airborne radioactivity exceeding the derived air concentration (DAC) or where there is a need to alert potentially exposed individuals to unexpected increases in airborne radioactivity levels. The DAC is the airborne concentration that equals the annual limit on intake divided by the volume of air breathed by an average worker for a working year of 2000 h (assuming a breathing volume of 2400 m{sup 3}). It is equivalent to the airborne concentration to which a worker could be exposed for an entire working year (2000 h) without exceeding the allowable annual limit on intake. The rule and the RCM further require that real-time air monitors have an alarm capability and sufficient sensitivity to alert potentially exposed individuals that immediate action is necessary in order to minimize or terminate inhalation exposures. The RCM also recommends that real-time air monitors should be capable of measuring 1 DAC when averagedmore » over 8 h (8 DAC-h) under laboratory conditions. In response to these recommendations, we are developing procedures for determining the basic sensitivity of alpha CAMs under laboratory conditions and for documenting practical alarm set points for routine use of CAMs under a range of radon and thoron concentrations.« less

Authors:
;
Publication Date:
Research Org.:
Lovelace Biomedical and Environmental Research Inst., Albuquerque, NM (United States). Inhalation Toxicology Research Inst.
OSTI Identifier:
54787
Report Number(s):
ITRI-144
ON: DE95007526; TRN: 95:012732
DOE Contract Number:
AC04-76EV01013
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Nov 1994; Related Information: Is Part Of Inhalation Toxicology Research Institute annual report, October 1, 1993--September 30, 1994; Belinsky, S.A.; Hoover, M.D.; Bradley, P.L. [eds.]; PB: 211 p.
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; 56 BIOLOGY AND MEDICINE, APPLIED STUDIES; 29 ENERGY PLANNING AND POLICY; RADIATION MONITORS; ALARM SYSTEMS; SENSITIVITY; RADIOACTIVE AEROSOLS; MAXIMUM INHALATION QUANTITY; ALPHA DECAY RADIOISOTOPES; AEROSOL MONITORING; PROGRESS REPORT

Citation Formats

Hoover, M.D., and Newton, G.J. Minimum detectable activity and false alarm rate relationships for alpha continuous air monitors. United States: N. p., 1994. Web.
Hoover, M.D., & Newton, G.J. Minimum detectable activity and false alarm rate relationships for alpha continuous air monitors. United States.
Hoover, M.D., and Newton, G.J. Tue . "Minimum detectable activity and false alarm rate relationships for alpha continuous air monitors". United States. doi:.
@article{osti_54787,
title = {Minimum detectable activity and false alarm rate relationships for alpha continuous air monitors},
author = {Hoover, M.D. and Newton, G.J.},
abstractNote = {The U.S. Department of Energy rule for Occupational Radiation Protection (10 CFR Part 835, December 1993) and the DOE Radiological Control Manual (the RCM) (DOE/EH-0256T, Rev. 1, April 1994) require the use of continuous air monitors (CAMs) in normally occupied areas where an individual is likely to be exposed to a concentration of airborne radioactivity exceeding the derived air concentration (DAC) or where there is a need to alert potentially exposed individuals to unexpected increases in airborne radioactivity levels. The DAC is the airborne concentration that equals the annual limit on intake divided by the volume of air breathed by an average worker for a working year of 2000 h (assuming a breathing volume of 2400 m{sup 3}). It is equivalent to the airborne concentration to which a worker could be exposed for an entire working year (2000 h) without exceeding the allowable annual limit on intake. The rule and the RCM further require that real-time air monitors have an alarm capability and sufficient sensitivity to alert potentially exposed individuals that immediate action is necessary in order to minimize or terminate inhalation exposures. The RCM also recommends that real-time air monitors should be capable of measuring 1 DAC when averaged over 8 h (8 DAC-h) under laboratory conditions. In response to these recommendations, we are developing procedures for determining the basic sensitivity of alpha CAMs under laboratory conditions and for documenting practical alarm set points for routine use of CAMs under a range of radon and thoron concentrations.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 1994},
month = {Tue Nov 01 00:00:00 EST 1994}
}

Technical Report:
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  • The U.S. Department of Energy rule for Occupational Radiation Protection and the DOE Radiological Control Manual (the RCM) (DOE/EH-0256T, Rev 1, April 1994) require the use of continuous air monitors (CAMs) in normally occupied areas there an individual is likely to be exposed to a concentration of airborne radioactivity exceeding the derived air concentration (DAC) or where there is need to alert potentially exposed individuals to unexpected increases in airborne radioactivity levels. The DAC is the airborne concentration that equals the annual limit on intake divided by the volume of air breathed by an average worker for a working yearmore » of 2,000 h (assuming a breathing volume of 2,400 m{sup 3}). It is equivalent to the airborne concentration to which a worker could be exposed for an entire year (2,000 h) without exceeding the annual limit on intake. The rule and the RCM further require that real-time air monitors have an alarm capability and sufficient sensitivity to alert potentially exposed individuals that immediate action is necessary in order to minimize or terminate inhalation exposures. The RCM also recommends that real-time air monitors should be capable of measuring 1 DAC when averaged over 8 h (8 DAC) under laboratory conditions. This report was prepared jointly with actual data from the CAMs in use at the WIPP by ITRI, WID, and EEG and provides an evaluation of minimum detectable activity (MDA) or concentration and false alarm rate relationships. The methodology used in this report is adapted from Inhalation Toxicology Research Institute Annual Report for 1993-1994, ITRI-144, pp 18-22, December 1994.« less
  • Eberline Alpha 6 and Alpha 6A continuous air monitors (CAMs) were tested against the performance criteria of the International Electrotechnical Commission standard 761-6, ``Equipment for Continuously Monitoring Radioactivity in Gaseous Effluents, Part 6: Specific Requirements for Transuranic Aerosol Effluent Monitors``, and against ANSI N42.17B, ``Performance Specification Health Physics Instrumentation--Occupational Airborne Radioactivity Monitoring Instrumentation``. The performance criteria require the CAM`s response to a radioactive source to remain within a tolerance while the CAM is exposed to an external influence such as temperature, electromagnetic fields, or ionizing radiations. The CAMs complied within specified tolerances with a majority of the performance specifications. Themore » most significant problems with CAM performance were noted during exposures to external nonionizing radiation fields (radio frequency fields). At numerous frequencies, the CAMs did not respond to radioactive material in the filter holder. At other frequencies and in some orientations, the CAMs overresponded by orders of magnitude. In addition to sensitivity to external nonionizing radiation fields, the CAMs exhibited sensitivity to electrostatic discharges.« less
  • For the past several years, we have supported the DOE Waste Isolation Pilot Plant (WIPP) project by evaluating the capabilities and performance of the Eberline Alpha 6 continuous air monitor (CAM). This evalution has focused on the ability of the CAM to correctly report plutonium in the presence of salt dust. Tests involving the simultaneous collection of plutonium and salt have shown that burial by salt can degrade the detection of plutonium, but that this interference is negligible when salt concentrations are below about 0.2 mg/m{sup 3}. Throughout the evalution, it has been assumed that salt burial is a concernmore » for slow, chronic release of plutonium, but that any acute release of plutonium would be collected on the top surface of the filter or salt and would be unattenuated. The spectral quality of alpha radiation detection on membrane filters is observed to improve with filter loading. This is attributed to the probability that accumulations of dust tend to fill in surface irregularities of the collection filter at a a faster rate than they create additional surface irregularities. The validity of these assumptions about the improved detection of plutonium on salt-layer surfaces has recently been questioned. Based on electron micrographic examination of salt-laden filters, it has been speculated that collection of salt dust on a membrane filter results in formation of pores, fissures, and dendritic shapes of salt on the filter surface. If plutonium were collected, particles could penetrate into the pores and fissures, resulting in a degraded or lost signal from the plutonium. Because no experimental evidence existed to answer the concern, the purpose of the current study was to quantify any differences between detection of plutonium on clean or salt-laden filters.« less
  • Alpha continuous air monitors (CAMs) will be used at the Waste Isolation Pilot Plant (WIPP) to measure airborne transuranic radioactivity that might be present in air exhaust or in work-place areas. WIPP CAMs are important to health and safety because they are used to alert workers to airborne radioactivity, to actuate air-effluent filtration systems, and to detect airborne radioactivity so that the radioactivity can be confined in a limited area. In 1993, the Environmental Evaluation Group (EEG) reported that CAM operational performance was affected by salt aerosol, and subsequently, the WIPP CAM design and usage were modified. In this report,more » operational data and current theories on aerosol collection were reviewed to determine CAM quantitative performance limitations. Since 1993, the overall CAM performance appears to have improved, but anomalous alpha spectra are present when sampling-filter salt deposits are at normal to high levels. This report shows that sampling-filter salt deposits directly affect radon-thoron daughter alpha spectra and overall monitor efficiency. Previously it was assumed that aerosol was mechanically collected on the surface of CAM sampling filters, but this review suggests that electrostatic and other particle collection mechanisms are more important than previously thought. The mechanism of sampling-filter particle collection is critical to measurement of acute releases of radioactivity. 41 refs.« less
  • We investigated a method to make optimum adjustments to the electronic background-subtract circuit of a continuous air monitor (CAM) by using a californium source instead of a background air sample. We observed spectra of detected alpha particles emitted by radon-thoron daughters and a californium source on a multichannel analyzer connected to a CAM to determine their effect on the behavior of the subtract circuit. The californium source alpha energy spectrum simulates the spectra of /sup 218/Po and /sup 212/Bi, the radon-thoron daughters most likely to cause spurious CAM alarms. This simulation was the basis for deriving an empirical method usingmore » californium to adjust the background-subtract circuit.« less