ГАММА-СПЕКТРОМЕТР ДЛЯ РАДИАЦИОННОГО МОНИТОРИНГА АКВАТОРИЙ И ДОННЫХ ОТЛОЖЕНИЙ

In order to solve the problem of continuous or periodic monitoring of water areas affected by radioactive contamination in the result of scheduled emissions in nuclear power plants or in the result of emergency situations in nuclear fuel cycle plants we need to develop measurement instruments with advanced mathematics and program support to assess the level of radioactive contamination with required accuracy. The aim of theoretical research was to optimize detection device construction, estimate spectrometer metrological parameters in given measurement geometries, and determine effective position of detection device in the process of in situ measurements. This device consists of spectrometric scintillation probe packed into sealed container (detection device) based on NaI(T1) crystal of Ø 63 × 63 mm or Ø 63 × 160 mm size, cable reel with deep-sea cable and a tablet PC for data processing and displaying. The container withstands static hydraulic pressure up to 5 MPa and can be used for measurements at depths of 500 m maximum. Probe measures energy distribution of gammaradiation with energy from 70 keV to 3000 keV. The implemented three-dimensional system for detection device position and orientation determination allows automatic operation of the device (without operator) for water areas or bottom sediment scanning. The spectrometer can output measurement results with threedimensional geographical coordinates as index maps of distribution with necessary resolution and accuracy. Monte Carlo models of spectrometer and controlled objects are developed in order to determine the detector response functions to given radionuclides in given measurement geometries without use of expensive standard measures of activity. Multifunction gamma-spectrometer for in situ radiation monitoring of water areas and bottom sediments was developed and constructed. In the result of theoretical researches the response functions have been calculated in the form of theoretical spectra of monitored radionuclides in definite measuring geometries. The results of mathematical modeling of the gamma-emitting transfer process allowed to estimate effective position of detection device for in situ measurements of specific activity radionuclides 134Cs and 137Cs in bottom sediments. Задачи постоянного или периодического мониторинга водоемов, подвергшихся радиоактивному загрязнению в результате штатных выбросов АЭС или в результате возникновения нештатных ситуаций на предприятиях топливного ядерного цикла, приводят к необходимости разработки соответствующих средств измерений с современным математическим и программным обеспечением, позволяющих оценить уровень радиоактивных загрязнений с заданной точностью. Цель теоретических исследований заключалась в оптимизации конструктива устройства детектирования, определении метрологических параметров спектрометра в заданных геометриях измерения, определении эффективного положения устройства детектирования спектрометра в процессе in situ измерений удельной активности радионуклидов 134Cs и 137Cs в донных отложениях с использованием разработанных Монте-Карло моделей: устройства детектирования, воды и донных отложений. Спектрометр представляет собой многофункциональный прибор, состоящий из размещаемого в герметичном контейнере спектрометрического сцинтилляционного блока детектирования с кристаллом NaI(T1) размерами Ø 63 × 63 мм или Ø 63 × 160 мм, вьюшки с глубоководным кабелем и планшетного компьютера для обработки и отображения информации. Контейнер устойчив к статическому гидравлическому давлению до 5 МПа, что позволяет проводить измерения на глубинах до 500 м. Устройство детектирования позволяет измерять энергетическое распределение импульсов гамма-излучения с энергией от 70 до 3000 кэВ. Реализованная система определения положения устройства детектирования в пространстве позволяет использовать спектрометр в автоматическом режиме (без участия оператора) для сканирования водной акватории и донных отложений. Результаты измерения заданной величины с трехмерными географическими координатами могут быть оперативно представлены в виде карт-схем распределения с необходимой дискретностью и точностью. Для определения функций отклика детектора к заданным радионуклидам в требуемых геометриях измерения без использования физических дорогостоящих стандартных мер активности разработаны Монте-Карло модели спектрометра и объектов контроля. Для радиационного контроля водной среды и донных отложений методом in situ разработан и изготовлен многофункциональный портативный гамма-спектрометр. В результате теоретических исследований были рассчитаны функции отклика спектрометра к контролируемым радионуклидам в заданных геометриях измерения. Результаты математического моделирования процесса переноса гамма-излучения позволили определить эффективную позицию устройства детектирования в процессе in situ измерений активности радионуклидов 134Cs и 137Cs в донных отложениях.

Влияние плотности почвы и характера распределения радионуклидов ¹³⁴Cs и ¹³⁷Cs по профилю при in situ измерениях

Periodic radiation monitoring of soils today is a priority task not only for Belarus, but also for Japan, suffered by Fukushima nuclear power plant accident. Use of portable and light spectrometers with ability to perform in situ measurements makes it possible to quickly estimate specific activity of measured radionuclides with required accuracy in particular soil site. Basic information of a gamma radiation source (radionuclides content, effective radius of measurement area and thickness of contaminated layer) can be obtained directly during measurement. The purpose of this research is to test the feasibility of using algorithms for determination of specific activity and thickness of contaminated layer under conditions of soil measurement with variable density parameters and radiocesium distribution in soil. Monte-Carlo simulating allowed to estimate the degree of deviation of the shape of simulated spectra obtained with the use of Monte-Carlo soil model with uniformly distributed radionuclide in it, and for the case when the radionuclide distribution by soil profile can be described by an exponential function. For these cases of natural distribution of radiocesium, the pulse-amplitude spectrum is formed by an effective thickness of the contaminated site, which contains more than 90 % of radionuclides. The developed Monte-Carlo model of a probe and contaminated soil site allows to estimate the effect of the variability of soil density on the total count rate of the pulse-amplitude spectrum. As a result of theoretical estimations, the relationship between the effective radius of contaminated site is determined as a function of soil density. Analysis of the influence of radial zones of the cylindrical gamma source on in situ gamma-spectrometer showed that the main contribution to the total count rate of the pulse-amplitude spectrum is made by the radial zone with radius of up to 40 cm from the center of the probe, regardless of the thickness of the contaminated layer in geometry «Probe is located on the soil surface». A small site facilitates the selection of measurement area of land with a sufficiently flat surface, which is desirable during surveying the territories, especially with complex terrain

Влияние плотности почвы и характера распределения радионуклидов ¹³⁴Cs и ¹³⁷Cs по профилю при in situ измерениях

Periodic radiation monitoring of soils today is a priority task not only for Belarus, but also for Japan, suffered by Fukushima nuclear power plant accident. Use of portable and light spectrometers with ability to perform in situ measurements makes it possible to quickly estimate specific activity of measured radionuclides with required accuracy in particular soil site. Basic information of a gamma radiation source (radionuclides content, effective radius of measurement area and thickness of contaminated layer) can be obtained directly during measurement. The purpose of this research is to test the feasibility of using algorithms for determination of specific activity and thickness of contaminated layer under conditions of soil measurement with variable density parameters and radiocesium distribution in soil. Monte-Carlo simulating allowed to estimate the degree of deviation of the shape of simulated spectra obtained with the use of Monte-Carlo soil model with uniformly distributed radionuclide in it, and for the case when the radionuclide distribution by soil profile can be described by an exponential function. For these cases of natural distribution of radiocesium, the pulse-amplitude spectrum is formed by an effective thickness of the contaminated site, which contains more than 90 % of radionuclides. The developed Monte-Carlo model of a probe and contaminated soil site allows to estimate the effect of the variability of soil density on the total count rate of the pulse-amplitude spectrum. As a result of theoretical estimations, the relationship between the effective radius of contaminated site is determined as a function of soil density. Analysis of the influence of radial zones of the cylindrical gamma source on in situ gamma-spectrometer showed that the main contribution to the total count rate of the pulse-amplitude spectrum is made by the radial zone with radius of up to 40 cm from the center of the probe, regardless of the thickness of the contaminated layer in geometry «Probe is located on the soil surface». A small site facilitates the selection of measurement area of land with a sufficiently flat surface, which is desirable during surveying the territories, especially with complex terrain

THE INFLUENCE OF SOIL DENSITY AND THE CHARACTER OF RADIOACTIVE 134Cs And 137Cs POLLUTION’S DISTRIBUTION ON in situ MEASUREMENTS

Periodic radiation monitoring of soils today is a priority task not only for Belarus, but also for Japan, suffered by Fukushima nuclear power plant accident. Use of portable and light spectrometers with ability to perform in situ measurements makes it possible to quickly estimate specific activity of measured radionuclides with required accuracy in particular soil site. Basic information of a gamma radiation source (radionuclides content, effective radius of measurement area and thickness of contaminated layer) can be obtained directly during measurement. The purpose of this research is to test the feasibility of using algorithms for determination of specific activity and thickness of contaminated layer under conditions of soil measurement with variable density parameters and radiocesium distribution in soil.Monte-Carlo simulating allowed to estimate the degree of deviation of the shape of simulated spectra obtained with the use of Monte-Carlo soil model with uniformly distributed radionuclide in it, and for the case when the radionuclide distribution by soil profile can be described by an exponential function. For these cases of natural distribution of radiocesium, the pulse-amplitude spectrum is formed by an effective thickness of the contaminated site, which contains more than 90 % of radionuclides.The developed Monte-Carlo model of a probe and contaminated soil site allows to estimate the effect of the variability of soil density on the total count rate of the pulse-amplitude spectrum. As a result of theoretical estimations, the relationship between the effective radius of contaminated site is determined as a function of soil density.Analysis of the influence of radial zones of the cylindrical gamma source on in situ gamma-spectrometer showed that the main contribution to the total count rate of the pulse-amplitude spectrum is made by the radial zone with radius of up to 40 cm from the center of the probe, regardless of the thickness of the contaminated layer in geometry «Probe is located on the soil surface». A small site facilitates the selection of measurement area of land with a sufficiently flat surface, which is desirable during surveying the territories, especially with complex terrain

ВЛИЯНИЕ ПЛОТНОСТИ ПОЧВЫ И ХАРАКТЕРА РАСПРЕДЕЛЕНИЯ РАДИОНУКЛИДОВ 134Cs И 137Cs ПО ПРОФИЛЮ ПРИ in situ Измерениях

Periodic radiation monitoring of soils today is a priority task not only for Belarus, but also for Japan, suffered by Fukushima nuclear power plant accident. Use of portable and light spectrometers with ability to perform in situ measurements makes it possible to quickly estimate specific activity of measured radionuclides with required accuracy in particular soil site. Basic information of a gamma radiation source (radionuclides content, effective radius of measurement area and thickness of contaminated layer) can be obtained directly during measurement. The purpose of this research is to test the feasibility of using algorithms for determination of specific activity and thickness of contaminated layer under conditions of soil measurement with variable density parameters and radiocesium distribution in soil.Monte-Carlo simulating allowed to estimate the degree of deviation of the shape of simulated spectra obtained with the use of Monte-Carlo soil model with uniformly distributed radionuclide in it, and for the case when the radionuclide distribution by soil profile can be described by an exponential function. For these cases of natural distribution of radiocesium, the pulse-amplitude spectrum is formed by an effective thickness of the contaminated site, which contains more than 90 % of radionuclides.The developed Monte-Carlo model of a probe and contaminated soil site allows to estimate the effect of the variability of soil density on the total count rate of the pulse-amplitude spectrum. As a result of theoretical estimations, the relationship between the effective radius of contaminated site is determined as a function of soil density.Analysis of the influence of radial zones of the cylindrical gamma source on in situ gamma-spectrometer showed that the main contribution to the total count rate of the pulse-amplitude spectrum is made by the radial zone with radius of up to 40 cm from the center of the probe, regardless of the thickness of the contaminated layer in geometry «Probe is located on the soil surface». A small site facilitates the selection of measurement area of land with a sufficiently flat surface, which is desirable during surveying the territories, especially with complex terrain.Проведение периодического радиационного мониторинга почв на сегодняшний день является одной из приоритетных задач для обеспечения радиационной безопасности не только в Беларуси, пострадавшей от Чернобыльской катастрофы, но и в Японии, территории которой подверглись радиоактивному загрязнению в результате аварии на АЭС Фукусима. Цель настоящей работы заключалась в проверке возможности применения разработанных на основе упрощенной («равномерной») модели алгоритмов определения активности и толщины загрязненного слоя в условиях радиометрии почвенного покрова с вариативными параметрами плотности и распределения радиоцезия по глубине.Использование портативных in situ спектрометров позволяет оперативно оценить удельную активность контролируемых радионуклидов и плотность загрязнения почвы прямо на месте измерения и с необходимой точностью. Основная информация об источнике гамма-излучения (присутствующие радионуклиды, эффективный радиус участка и толщина загрязненного слоя) может быть получена непосредственно по результатам измерения аппаратурного спектра в сравнении с теоретическими (калибровочными) спектрами. Теоретические спектры рассчитывают путем имитационного моделирования процесса in situ измерений активности радионуклидов 134Cs и 137Cs, равномерно распределенных в однородной почвенной среде постоянной плотности. На практике следует учитывать приблизительность принятой модели измерений в отношении реального профиля заглубления радиоактивных загрязнений и изменчивости плотности исследуемых почв.Анализ влияния радиальных зон цилиндрического источника на интегральную скорость счета спектрометра показал, что основной вклад вносят радиальные зоны в радиусе до 40 см от центра устройства детектирования при расположении его на поверхности почвы вне зависимости от толщины загрязненного слоя. Небольшая по площади зона влияния облегчает выбор контролируемых участков земли с достаточно плоской поверхностью, что желательно при обследовании территорий, особенно со сложным рельефом