Minimum measurable activity: The concept and its application in radiometry

Григорьев, Е. И.; Stepanov, É. K.; Fominykh, V.I.; Kharitonov, I. A.; Yaryna, V. P.

doi:10.1007/bf00976926

Cited by 3 publications

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“…The minimum activity -the activity which can be measured by technical means over 1 h with statistical error 50% and confidence probability 0.95 -determines the measuring possibilities of radiometers and spectrometers [6]. For the case where the increment to the counting rate due to radiation of a radionuclide in the region of detection n i is less than the background counting rate in this region n b (n i < n b ), the minimum activity is determined as MMA = 0.1n b 1/2 /S TAP .…”

Section: Calculation Of Gamma Spectrometer Characteristics Using Modementioning

confidence: 99%

Use of model sources for measuring radiation emissions and calculation of gamma spectrometer characteristics

Lavrukhin

Rumyantsev

2008

At Energy

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Methodological questions concerning the use of gamma spectrometers for measuring gas-aerosol emissions from nuclear power plants and radiation monitoring of the environment by remote gamma spectrometry are examined. A system of intercoupled programs was developed to solve this problem. This system makes it possible to calculate the energy-angular distribution of the gamma ray flux created at the monitoring point from a uniform extended volume source with user-prescribed characteristics and measuring geometry. The computational result is used as a source for direct simulation of the line shape in the NaI(Tl) crystal spectrometer used.Determining the emission intensity in real time for normal operation and in accident situations requires developing a gamma-spectrometric channel for performing remote measurements of the volume activity of radionuclides in the atmospheric layer near the ground. Gamma spectrometers based on semiconductor detectors, high-pressure xenon chambers, or inorganic scintillators can be used as detectors in such a channel. When such a spectrometer is inserted in a channel of an automated system for monitoring radiation conditions, it becomes necessary to measure the main metrological characteristics -the sensitivity and the minimum measurable volume activity of radionuclides. The fact that it is impossible to create artificial extended volume sources with spectral characteristics similar to those of real sources and to calibrate them for diverse geometries complicates the determination of these characteristics.Similar problems arise with the use of direct continuous gamma spectrometric methods for monitoring the atmospheric layer near the ground.Radionuclides in a gas-aerosol emissions stream can be regarded as an extended volume source, creating in the environment a radiation field whose main parameters are the energy flux density, the gamma ray flux density, and the exposure rate or absorbed dose. Switching to gamma spectrometric monitoring methods, the gamma ray flux density and its angular distribution must be determined at the location of the spectrometer. Knowing these quantities makes it possible to calculate the volume activity of radionuclides in the stream at the monitoring site and, using an appropriate model of their transport, to estimate the magnitude of the emission.A special system of intercoupled programs was developed at the KonverSia JSC to solve these problems. This system makes it possible to perform a Monte Carlo calculation of the energy-angular distribution of the gamma ray flux at the monitoring point from a uniform extended volume source with a prescribed radionuclide composition, volume activity, and measuring geometry. This distribution is then used as a source for direct simulation of the line shape in the scintillation detector of the spectrometer [1]. The CLOUD computer program calculates the energy-angular distribution of the gamma ray flux and the absorbed dose rate in air from an ellipsoidal source. These same characteristics can be calculated using as a volum...

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Section: Calculation Of Gamma Spectrometer Characteristics Using Modementioning

confidence: 99%

Use of model sources for measuring radiation emissions and calculation of gamma spectrometer characteristics

Lavrukhin

Rumyantsev

2008

At Energy

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“…One of the main characteristics of a radiometer is the lowest measurable activity, which determines the lowest activity measured with a 50% error over an exposure time of 1 h. This quantity can be found by using the concept of the background uncertainty in measuring zero activity R ∆ 0 (τ) [5]:…”

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“…97, 25 [2][3][4][5] or in surface trench-type repositories with clay serving to isolate the wastes from water (repository Nos. 25 1,7 , 205 1,2 ).…”

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Radiation survey of radioactive objects at the Kirovo-Chepetsk chemical combine

et al. 2009

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The methods and means for performing a radiation survey of objects and grounds of the Kirovo-Chepetsk Chemical Combine are presented. Results of a survey of rooms in the combine and measurements of soil contamination levels on the grounds and of the specific activity of samples of radioactive wastes in temporary repositories and slag dumps are presented. The surveys make it possible to develop a concept and a project for rehabilitating these objects and grounds and to choose a technology for handling radioactive wastes during liquidation or preservation of repositories.In 2007-2008, specialists from the Russian Science Center Kurchatov Institute, Moscow Scientific and Industrial Association Radon, and the Center for the Administration of Federal Property examined radioactively contaminated objects and grounds of the Kirovo-Chepetsk Chemical Combine in order to collect data on the contamination of buildings, where work on the reprocessing of uranium raw material was terminated, as well as sludge and radwaste repositories. At the same time, it was discovered that individual areas on the grounds of the combine were radioactively contaminated as a result of the handling of radwastes as well as the presence of equipment contaminated at the early stages of the development of the technology for reprocessing uranium hexa-and tetrafluoride. In addition, it was necessary to determine the volumes of remediation work, identify the most critical objects and grounds, and develop remediation steps. Models of radionuclide migration in environmental objects and forecasts of radionuclide propagation in the next few years will be developed on the basis of these data.Basic Reasons for the Radioactive Contamination of Objects and Grounds. The Kirovo-Chepetsk Chemical Combine is located on the western edge of the town of Kirovo-Chepetsk. The production of uranium hexafluoride was set up there in the 1940s. Facility No. 93 for the production of uranium tetrafluoride was started up there in 1954 and reached its full production capacity in 1955. Initially, it was assumed that this facility would use secondary uranium which had been irradiated in a reactor. After the irradiated uranium was dissolved and the plutonium and most of the fission products in the form of uranyl-sodium diacetate salt had been removed from it, the irradiated uranium entered facility No. 93 for reprocessing into uranium tetrafluoride and then into facility No. 2 for the production of uranium hexafluoride [1]. In 1961, specialists at the combine and at the All-Russia Research Institute of Chemical Technology (VNIIKhT) developed a technology for repro-

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“…According to the results of yearly observations, when calculating the thresholds in all energy intervals (with the exception of the integral interval) k α = 3.75 gave one false actuation of the Matros algorithm over 100 h and P f.a ≤ 10 -3 . Increasing the threshold narrows the range of the concentrations of the radionuclides being detected for prescribed correct detection and false alarm probabilities, since the upper limit of detection, determined by the lowest measureable activity, is 7.6N ij 1/2 over 15 min of measurements [8].…”

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Detection of technogenic radionuclides at low concentrations when monitoring nuclear power plant emissions using an arms spectrometric channel

2010

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The application of statistical algorithms in the problem of early detection of technogenic, nuclear power plant emissions in the atmosphere near the ground by means of the spectrometric channel of ARMS (Automatic Radiation Monitoring System) is examined. It is noted that the changes in the radon progeny content which are associated with the diurnal behavior of the intensity of turbulent mixing influence the variance of the readings in the 131 I and 137 Cs detection ranges. As a result, when a stationary Poisson model is used in the algorithm the number of false alarms increases and the algorithm becomes ineffective. Regional corrections lowering the probability of false alarms to ≤10 -3 with correct detection probability ≥0.7 were introduced into the detection and classification algorithm on the basis of the results of monitoring performed over the course of a year for intervals with stationary γ background.When the ARMS (Automatic Radiation Monitoring System) spectrometric channel is used for early detection of nuclear power plant emissions, technogenic radionuclides at low concentrations must be detected with a definite reliability in real-time. Ordinarily, the lowest measurable activity, determined by the background conditions in the monitoring zone and the method and means for performing the measurements, is taken as the conventional boundary between the detection and measurement processes. Our assessments have shown that a gamma spectrometer with a 63 × 63 mm NaI(Tl) crystal with exposure time 15 min can be used for quantitative measurements of 131 I and 137 Cs provided that their volume activity ≥8 Bq/m 3 , i.e., starting at values 2-3 times lower than the admissible volume activity AVA PUBLIC according to . Statistical algorithms for processing the spectrometric information make it possible to detect 131 I and 137 Cs with probability ≥0.7 at concentrations concentration 2-3 Bq/m 3 , which expands the possibility of using the ARMS spectrometric channel for monitoring nuclear power plant emissions. In what follows, the term "detection" is used precisely in this probabilistic sense, since, for example, according to Rosgidromet normative documents the detection of a radionuclide not present in the global radiation background is taken as a level of detection two times above the minimum measurable activity of the radionuclide for the apparatus being using [2].The concept of the minimum detectable volume activity can be introduced as a characteristic of the spectrometric channel for detecting technogenic radionuclides at low concentrations under background conditions in the ARMS monitoring zone. It can be determined as the volume activity which is detected by the algorithm used for processing the spectrometric information with probability of correct detection P c.d and false-alarm probability P f.a established for the given ARMS.

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Minimum measurable activity: The concept and its application in radiometry

Cited by 3 publications

References 0 publications

Use of model sources for measuring radiation emissions and calculation of gamma spectrometer characteristics

Use of model sources for measuring radiation emissions and calculation of gamma spectrometer characteristics

Radiation survey of radioactive objects at the Kirovo-Chepetsk chemical combine

Detection of technogenic radionuclides at low concentrations when monitoring nuclear power plant emissions using an arms spectrometric channel

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