Further development and application of a method for assessing radionuclide surface activity distribution and source location based on measurements of ambient dose equivalent rate.

A method has been developed for solving the Fredholm equation in the barrier geometry for reconstructing the surface activity density (SAD) from the results of measuring the ambient dose equivalent rate (ADER). Inclusion of the barrier geometry means that the method takes into account the shielding effect of buildings and structures on the contaminated site. The method was based on the representation of the industrial site, buildings and radiation fields in the form of a raster and the use of the visibility matrix (VM) of raster cells to describe the barrier geometry. The developed method was applied to a hypothetical industrial site with a size of 200 × 200 conventional units for four types of SAD distribution over the surface of the industrial site: 'fragmentation', 'diffuse', 'uniform' and 'random'. The method of Lorentz curves was applied to estimate the compactness of the distributions of SAD and the ADER for the considered radiation sources. It was shown that the difference between the Lorentz curve for SAD and ADER means that the determination of the spatial distribution of SAD over the industrial site by solving the integral equation is essentially useful for determining the location of radiation source locations on the industrial site. The accuracy of SAD reconstruction depends on the following parameters: resolution (fragmentation) of the raster, the height of the radiation detector above the scanned surface, and the angular aperture of the radiation detector. The measurement of ADER is simpler and quicker than the direct measurement of SAD and its distribution. This represents a significant advantage if SAD distribution needs to be determined in areas with high radiation dose-rate during limited time. The developed method is useful for supporting radiation monitoring and optimizing the remediation of nuclear legacies, as well as during the recovery phase after a major accident.

Further development and application of a method for assessing radionuclide surface activity distribution and source location based on measurements of ambient dose equivalent rate. Examples for Andreeva Bay, Chernobyl NPP and Istiklol.

A method for reconstructing surface activity density (SAD) maps based on the solution of the Fredholm equation has been developed and applied. The construction of SAD maps was carried out for the site of the temporary storage (STS) of spent fuel and radioactive waste (RW) in Andreeva Bay using the results of measuring campaign in 2001-2002 and for the sheltering construction of the solid RW using the results of measurements in 2021. The Fredholm equation was solved in two versions: under conditions of a barrier-free environment and taking into account buildings and structures located on the industrial site of the STS Andreeva Bay. Lorenz curves were generated to assess the compactness of the distributions of SAD and ambient dose equivalent rate (ADER) for the industrial site and the sheltering construction at STS Andreeva Bay, the area of the IV stage uranium tailing site near the city of Istiklol in the Republic of Tajikistan, and for roofs of the Chernobyl nuclear power plant. The nature of impact of the resolution (fragmentation) of the raster, the value of the radius of mutual influence of points (contamination sites), the height of the radiation detector above the scanned surface and the angular aperture of the radiation detector on the accuracy of the SAD reconstruction is shown. The method developed allows more accurate planning of decontamination work when only ADER measurements data is available. The proposed method can be applied to support the process of decontamination of radioactively contaminated territories, in particular during the remediation of the STS Andreeva Bay.

Are dietary reports in a case-control study on thyroid cancer biased by risk perception of Chernobyl fallout?

BACKGROUND: In retrospective case-control studies performed following nuclear tests or nuclear accidents, individual thyroid radiation dose reconstructions are based on fallout and meteorological data from the residential area, demographic characteristics, and lifestyle as well as dietary information. Collecting the latter is a controversial step, as dietary declarations may be affected by the subjects' beliefs about their risk behavior. This report analyses the potential for such bias in a case-control study performed in eastern France. METHODS: The study included 765 cases of differentiated thyroid carcinoma matched with 831 controls. Risk perceptions and beliefs of cases and controls were compared using Chi2 tests and differences in dietary reports were analyzed using a two-way ANOVA. RESULTS: In general, atmospheric pollution and living near a nuclear power plant were the two major risks that may influence thyroid cancer occurrence cited by cases and controls. When focusing in particular on the consequences of the Chernobyl accident, cases were more likely to think that the consequences were responsible for thyroid cancer occurrence than controls. Vegetable consumption during the two months after the Chernobyl accident was correlated with the status of subjects, but not to their beliefs. Conversely, consumption of fresh dairy products was not correlated with the status or beliefs of subjects. CONCLUSION: We found no evidence of systematic bias in dietary reports according to the status or beliefs held by subjects about the link between thyroid cancer occurrence and Chernobyl fallout. As such, these dietary reports may be used in further studies involving individual dosimetric reconstructions.

Thyroid cancer risk in Belarus among children and adolescents exposed to radioiodine after the Chornobyl accident.

BACKGROUND: Previous studies showed an increased risk of thyroid cancer among children and adolescents exposed to radioactive iodines released after the Chornobyl (Chernobyl) accident, but the effects of screening, iodine deficiency, age at exposure and other factors on the dose-response are poorly understood. METHODS: We screened 11 970 individuals in Belarus aged 18 years or younger at the time of the accident who had estimated (131)I thyroid doses based on individual thyroid activity measurements and dosimetric data from questionnaires. The excess odds ratio per gray (EOR/Gy) was modelled using linear and linear-exponential functions. RESULTS: For thyroid doses <5 Gy, the dose-response was linear (n=85; EOR/Gy=2.15, 95% confidence interval: 0.81-5.47), but at higher doses the excess risk fell. The EOR/Gy was significantly increased among those with prior or screening-detected diffuse goiter, and larger for men than women, and for persons exposed before age 5 than those exposed between 5 and 18 years, although not statistically significant. A somewhat higher EOR/Gy was estimated for validated pre-screening cases. CONCLUSION: 10-15 years after the Chornobyl accident, thyroid cancer risk was significantly increased among individuals exposed to fallout as children or adolescents, but the risk appeared to be lower than in other Chornobyl studies and studies of childhood external irradiation.

THYROID SCREENING AND RELIABILITY OF RADIATION THYROID DOSES FOR THE BELARUSIAN IN UTERO COHORT.

OBJECTIVE: To describe the status and results of thyroid disease screening and assessment of reliability of radiationthyroid doses in the Belarusian in utero cohort of 2,965 individuals exposed to Chernobyl (Chornobyl) fallout. MATERIALS AND METHODS: Thyroid screening examinations are currently underway including thyroid palpation by anendocrinologist, ultrasonographic examination by an ultrasonographer and analysis of blood samples for diagnosisof hypo- and hyperthyroidism, autoimmune thyroiditis, thyroid function tests (thyroid-stimulating hormone [TSH],thyroxine [T4], thyroid peroxidase antibody [anti-TPO], and thyroglobulin antibodies [anti-TG]). Reliability of (i)information from 780 pairs of questionnaires obtained during the first and second interviews of the mothers and (ii)thyroid doses, which were calculated for the cohort members using this information, is evaluated. RESULTS: As of 15 August 2021, 1,267 in utero exposed study subjects had been screened. A single thyroid nodule wasdiagnosed in 167 persons (13.2 % of the total) and multiple thyroid nodules in 101 persons (8.0 %): 189 (14.9 %)persons had nodules detected for the first time at the screening while 79 (6.2 %) persons had nodules detected pre-viously (pre-screening nodules). Fifty-nine out of 268 subjects (22.0 %) with a suspicious thyroid nodule werereferred to fine needle aspiration biopsy, and among them 33 (55.9 %) were biopsied. Reasonable agreement wasobserved for modelqbased doses calculated for the Belarusian in utero cohort members using data from the two inter-views (Spearman's rank-correlation coefficient rs = 0.74, p < 0.001), while measurementqbased doses yielded almost per-fect agreement (rs = 0.99, p < 0.001). CONCLUSIONS: During the thyroid screening, at least one thyroid nodule was identified in 268 of 1,267 (21.2 %) inutero exposed cohort members. Seven thyroid cancer cases were identified in the cohort, including 5 pre-screeningcases and 2 cases detected during the screening. Ongoing research on this unique cohort will provide importantinformation on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocesium iso-topes, for which available epidemiological data are scant.

Thyroid cancer following nuclear tests in French Polynesia.

BACKGROUND: Between 1966 and 1974, France conducted 41 atmospheric nuclear tests in Polynesia, but their potential health effects have not previously been investigated. METHODS: In a case-control study, we compared the radiation exposure of almost all the French Polynesians diagnosed with differentiated thyroid carcinoma between 1981 and 2003 (n=229) to the exposure of 373 French Polynesian control individuals without cancer from the general population. Radiation exposures were estimated using measurements after the nuclear tests, age at time of each test, residential and dietary information. RESULTS: The average thyroid dose before 15 years of age was about 1.8 mGy, and 5% of the cases and 3% of the controls received a dose above 10 mGy. Despite this low level of dose, and after adjusting for ethnic group, level of education, body surface area, family history of thyroid cancer and number of pregnancies for women, we observed an increasing risk (P=0.04) of thyroid cancer with increasing thyroid dose received before age of 15 years, which remained after excluding non-aggressive differentiated thyroid micro-carcinomas. This increase of risk per unit of thyroid radiation dose was higher (P=0.03) in women who later experienced four or more pregnancies than among other women. CONCLUSION: The risk estimate is low, but is based on limited exposure data. The release of information on exposure, currently classified, would greatly improve the reliability of the risk estimation.

RECONSTRUCTION OF THE RADIOACTIVE CONTAMINATION OF THE TERRITORY OF UKRAINE BY IODINE-131 DURING INITIAL PERIOD OF THE CHORNOBYL ACCIDENT USING THE RESULTS FROM NUMERICAL MODEL WRF. / REKONSTRUKTsIIa RADIOAKTYVNOGO ZABRUDNENNIa TERYTORIÏ UKRAÏNY IODOM-131 V POChATKOVYI PERIOD ChORNOBYL'S'KOÏ AVARIÏ Z VYKORYSTANNIaM ChYSEL'NOÏ MODELI WRF.

OBJECTIVE: To reconstruct the 131I activity concentrations in air and 131I ground deposition densities from 26 April to7 May 1986 from the radioactivity release after the Chornobyl accident in the settlements of Ukraine using themesoscale radionuclides atmospheric transport model LEDI and meteorological information from the numericalweather forecast model WRF and to compare the obtained results with those calculated previously as well as withavailable measurements of 131I activity in soil.Object of research: the near-ground layer of the atmosphere and the surface of the territory of Ukraine radioactively contaminated as a result of the Chornobyl accident.Materials and methods of research. The dispersion of 131I in the atmosphere and deposition on the ground surfacein Ukraine were calculated using the Lagrangian-Eulerian diffusion model LEDI. The detailed fields of meteorological parameters calculated using the mesoscale weather forecast model WRF, which was adapted for the territory ofUkraine, were used as input data for the LEDI model. RESULTS: The 131I daily-average activity concentrations in the surface air and 131I daily ground deposition densitiesfrom 26 April to 7 May 1986 were calculated using the up-to-date mesoscale model of numerical weather forecastWRF for 30,352 settlements in entire Ukraine, including 1,263 settlements in Kyiv, 1,717 - in Zhytomyr and 1,570 -in Chernihiv Oblasts. CONCLUSIONS: The method of mathematical modeling of the atmospheric transport of the radionuclides is combination with the up-to-date mesoscale model of numerical weather forecast WRF is a useful tool for reconstruction ofradioactive contamination of the air and the ground surface after the Chornobyl accident. Calculated in this study131I activity concentrations in air and 131I ground deposition densities were used to reconstruct the thyroid doses dueto 131I intake to the population of Ukraine.

Uncertainties in individual doses in a case-control study of thyroid cancer after the Chernobyl accident.

Individual radiation doses to the thyroid were reconstructed for 2239 subjects of a case-control study of thyroid cancer among young people that was carried out in regions of Belarus and Russia contaminated by radioactive fallout from the Chernobyl accident. Although the process of dose reconstruction provides a point estimate of each subject's dose, it is obvious that there is uncertainty associated with these dose calculations. The following main sources of uncertainty in the estimated individual doses were identified: (1) shared and unshared errors associated with parameters of the dosimetry model; and (2) unshared errors that are associated with the variability, reliability and ability of information from the personal interviews. Besides setting up proper distributions for the parameters of the dosimetry model, inter-individual correlations were also defined to take into account shared errors. By the application of Monte Carlo simulations, a set of approximately log-normally distributed thyroid doses was obtained for each subject; the geometric standard deviations of the distributions are found to vary among individuals from 1.7 to 3.7.

Radiation exposure to the population of Europe following the Chernobyl accident.

On the occasion of the 20th anniversary of the Chernobyl accident an attempt has been made to evaluate the impact of the Chernobyl accident on the global burden of human cancer in Europe. This required the estimation of radiation doses in each of the 40 European countries. Dose estimation was based on the analysis and compilation of data either published in the scientific literature or provided by local experts. Considerable variability has been observed in exposure levels among the European populations. The average individual doses to the thyroid from the intake of (131)I for children aged 1 y were found to vary from approximately 0.01 mGy in Portugal up to 750 mGy in Gomel Oblast (Belarus). Thyroid doses to adults were consistently lower than the doses received by young children. The average individual effective doses from external exposure and ingestion of long-lived radiocaesium accrued in the period 1986-2005 varied from approximately 0 in Portugal to approximately 10 mSv in Gomel Oblast (Belarus) and Bryansk Oblast (Russia). The uncertainties in the dose estimates were subjectively estimated on the basis of the availability and reliability of the radiation data that were used for dose reconstruction in each country.

Measurement of 129 I and 137 Cs in soils from Belarus and reconstruction of 131I deposition from the Chernobyl accident.

I and Cs have been measured in a large number of soil samples collected throughout the country of Belarus to support efforts for thyroid-dose reconstruction following the Chernobyl accident. Samples of soil consisting of multiple 30-cm-deep cores per site were sampled following a selection process to ensure sites were undisturbed and representative. Samples were measured by accelerator mass spectrometry (AMS) for I, gamma spectrometry for Cs, and gas chromatography (GC) for total iodine. Results show that both I and Cs are retained firmly in the top approximately 15 to 20 cm of the soil. Our results also suggest that the correlation between I and Cs deposition across the country of Belarus is poor; hence, I is a better surrogate for I than is Cs. It was also noted that total iodine concentrations in topsoil from Belarus are low compared with other regions of the world where radiogenic thyroid cancer has been studied.

Using total beta-activity measurements in milk to derive thyroid doses from Chernobyl fallout.

Following the Chernobyl accident, more than 200 childhood thyroid cancer cases have been observed in Brest Oblast of Belarus in territories slightly contaminated with 137Cs, but with suspected relatively high 131I fallout. The most helpful measurements available that can be used to estimate thyroid doses for the population of Brest Oblast are the total beta-activity measurements in cow's milk performed using DP-100 device within a few weeks after the accident. The 131I concentrations in milk were derived from the total beta-activity measurements on the basis of (1) a radioecological model used to estimate the variation with time of the radionuclide composition in milk and (2) the determination of the calibration factors of the DP-100 device for the most important radionuclides present in milk. As a result, 131I concentrations in milk were reconstructed for territories with different levels of 137Cs deposition. A non-linear dependence of the 131I concentration in milk on the 137Cs deposition density was obtained; it was used to estimate the thyroid doses from the consumption of 131I-contaminated cow's milk by the population of Brest Oblast. The average individual thyroid doses have been estimated to be 0.15, 0.18, 0.12, 0.06, 0.04 and 0.03 Gy for newborn, children aged 1, 5, 10 and 15 y and adults, respectively. The collective thyroid dose for the entire population of Brest Oblast is estimated to be 64,500 man Gy, the contribution from the adult population being about one half of the total. The methodology that is described could be applied in the framework of epidemiological studies of the relationship between radiation exposure to the thyroid gland and thyroid cancer in areas where numerous total beta-activity measurements in cow's milk were performed within a few weeks after the accident.

Chernobyl-related thyroid cancer in children of Belarus: a case-control study.

The accident at the Chernobyl nuclear power plant on April 26, 1986, released approximately 2 EBq of 131I and other radioiodine isotopes that heavily contaminated southern Belarus. An increase in thyroid cancer reported in 1992 and attributed to the Chernobyl accident was challenged as possibly the result of intensive screening. We began a case-control study to test the hypothesis that the Chernobyl accident caused the increase in thyroid cancer. Records of childhood thyroid cancer in the national therapy centers in Minsk in 1992 yielded 107 individuals with confirmed pathology diagnoses and available for interview. Pathways to diagnosis were (1) routine endocrinological screening in 63, (2) presentation with enlarged or nodular thyroid in 25 and (3) an incidental finding in 19. Two sets of controls were chosen, one matched on pathway to diagnosis, the other representing the area of heavy fallout, both matched on age, sex and rural/urban residence in 1986. The 131I dose to the thyroid was estimated from ground deposition of 137Cs, ground deposition of 131I, a data bank of 1986 thyroid radiation measurements, questionnaires and interviews. Highly significant differences were observed between cases and controls (both sets) with respect to dose. The differences persisted within pathway to diagnosis, gender, age and year of diagnosis, and level of iodine in the soil, and were most marked in the southern portion of the Gomel region. The case-control comparisons indicate a strong relationship between thyroid cancer and estimated radiation dose from the Chernobyl accident.

The intellectual development, mental and behavioural disorders in children from Belarus exposed in utero following the chernobyl accident.

The study examined psychological development in 250 children at the age of 6-7 and 10-12 years who had been exposed in the prenatal period at the time of the Chernobyl accident in 1986. These children were compared to a control group of 250 children of the same age from non- and slightly contaminated areas of Belarus. The examination included psychiatric examination and intellectual assessment as well as the estimation of thyroid exposure in utero. The mean value of thyroid doses from (131)I 0.39 Gy was estimated for the prenatal exposed children. The children of the exposed group had a lower mean full-scale IQ compared to the control group (89.6 +/- 10.2 vs 92.1 +/- 10.5 at the age of 6-7 years, P = 0.007; and 94. 3 +/- 10.4 vs 95.8 +/- 10.9 at the age of 10-12 years, P = 0.117). Average IQ for the subgroup of highly exposed children (thyroid doses more than 1 Gy) was lower in comparison with average IQ for the whole exposed group (85.7 +/- 6.4 vs 89.6 +/- 10.2 at the age of 6-7 years, P = 0.014; 89.1 +/- 7.1 vs 94.3 +/- 10.4 at age 10-12 years, P = 0.003). No statistically significant distinctions in average IQ were found between the different subgroups of children in relation to the gestational age at the time of the Chernobyl accident. We notice a positive moderate correlation between IQ of children and the educational level of their parents (in exposed group - mothers: r = 0.50, P < 0.01 and fathers: r = 0.52, P < 0.01; in control group - mothers: r = 0.41, P < 0.05 and fathers: r = 0.42, P < 0.05). There was a moderate correlation between high personal anxiety in parents and emotional disorders in children (for mothers r = 0.38, P < 0.05; for fathers r = 0.43, P < 0.01). The relative risk of mental and behavioural disorders has been estimated for emotional disorders OR = 2.67, P < 0.001. The frequency of the formation of mental retardation, hyperkinetic disorders and other mental and behavioural disorders in children from both groups was approximately the same. We conclude that in the genesis of borderline intellectual functioning and emotional disorders in the exposed group of children a significant role was probably played by unfavourable social-psychological and sociocultural factors such as a low educational level of the parents, the break of microsocial contacts and difficulties adapting, which appeared following the evacuation and relocation from the contaminated areas.

The feasibility of using 129I to reconstruct 131I deposition from the Chernobyl reactor accident.

Radioiodine released to the atmosphere from the accident at the Chernobyl nuclear power station in the spring of 1986 resulted in large-scale thyroid-gland exposure of populations in Ukraine, Belarus, and Russia. Because of the short half life of 131I (8.04 d), adequate data on the intensities and patterns of iodine deposition were not collected, especially in the regions where the incidence of childhood-thyroid cancer is now increasing. Results are presented from a feasibility study that show that accelerator-mass-spectrometry measurements of 129I (half life 16 x 106 y) in soil can be used to reconstruct 131I-deposition density and thus help in the thyroid-dosimetry effort that is now urgently needed to support epidemiologic studies of childhood-thyroid cancer in the affected regions.

Influence of radionuclides distributed in the whole body on the thyroid dose estimates obtained from direct thyroid measurements made in Belarus after the Chernobyl accident.

Thyroid dose reconstruction is most accurate when using the results of direct thyroid measurements, in which gamma radiation emitted by radionuclides present in the thyroid and in the remainder of the body is recorded by means of a radiation detector positioned against the neck. A large number of such measurements were performed in Belarus in May-June 1986. Owing to the short half-life of 131I and to the intake and accumulation of caesium radioisotopes (mainly 134Cs and 137Cs) in the body, the thyroid doses derived from thyroid measurements made after the beginning of June 1986 have so far been often considered to be unreliable. To evaluate the influence of the caesium radioisotopes to the signal recorded by an instrument performing measurement of 131I activity in the thyroid, a Monte Carlo method was used to calculate the calibration factors of that instrument. These calculations were made for males of six reference ages: newborn, 1, 5, 10 and 15 years old, and adult. The calibration factors were combined with estimated time-dependent intake functions for 131I and caesium radioisotopes. The fractions of the instrument indications that were due to 131I in thyroid were thus estimated as a function of the age of the subject that was measured and of the time elapsed since the accident. Using this information when processing the thyroid measurements made in May 1986 would improve the accuracy of the thyroid dose estimates, and may make it possible to use a larger proportion of the thyroid measurements made in June 1986.

Estimation of the thyroid doses for ukrainian children exposed in utero after the chernobyl accident.

This paper describes methods for estimating thyroid doses to Ukrainian children who were subjects of an epidemiological study of prenatal exposure and presents the calculated doses. Participants were 2,582 mother-child pairs in which the mother had been pregnant at the time of the Chernobyl accident on 26 April 1986 or in the 2-3 mo following when (131)I in fallout was still present. Among these, 1,494 were categorized as "exposed;" a comparison group of 1,088 was considered "relatively unexposed." Individual in utero thyroid dose estimates were found to range from less than 1 mGy to 3,200 mGy, with an arithmetic mean of 72 mGy. Thyroid doses varied primarily according to stage of pregnancy at the time of exposure and level of radioactive contamination at the location of residence. There was a marked difference between the dose distributions of the exposed and comparison groups, although nine children in the latter group had calculated doses in the range 100-200 mGy. For those children who were born after the accident and prior to the end of June 1986, postnatal thyroid doses were also estimated. About 7.7% (200) of the subjects received thyroid doses after birth that were at least 10% of their cumulative doses.

Thyroid mass in children and adolescents living in the most exposed areas to Chernobyl fallout in Belarus.

This paper aims to determine the thyroid volumes in children and teenagers living in Gomel and Mogilev Oblasts, which are the areas of Belarus that were most affected by the Chernobyl accident. Results of thyroid volume measurements performed in 1991-1996 by the Sasakawa Memorial Health Foundation were used to evaluate the variation by age of the thyroid volumes for girls and boys aged from 5 to 16 y. Thyroid volumes for age groups without measurements were also estimated. For a given age and gender, the differences between children from Gomel and Mogilev Oblasts do not exceed 12 %, which is relatively small when the variability of individual values is considered. For children of a given age, the individual values show a variability characterised by geometric standard deviation (GSD) of 1.25-1.4. Values of thyroid mass that were derived from the measured thyroid volumes are being used within the framework of the on-going Belarusian-American cohort study of thyroid cancer and other thyroid diseases after the Chernobyl accident to estimate with more accuracy the thyroid doses that were received by the cohort members.

The utility of focus group interviews to capture dietary consumption data in the distant past: dairy consumption in Kazakhstan villages 50 years ago.

From 1949 to 1962, residents of several villages in Kazakhstan received substantial doses of radiation to the thyroid gland resulting from nuclear tests conducted at the Semipalatinsk Nuclear Test Site. The primary source of radiation was internal from an intake of radioactive iodine by consumption of contaminated dairy products. A previous research study of childhood exposure and thyroid disease in this region gathered limited data on study participants' dairy intake at the time of the fallout for the purpose of estimating past radiation doses. As many participants were too young at the time of the nuclear tests to recall dietary consumption and existing sources of archival data are limited, it was necessary to interview parents and other village residents who cared for children during this time - older adults ranging in age from 75 to 90 years. Results from 11 focus group interviews conducted in 2007 with 82 women from 4 villages in Kazakhstan yielded group-level estimates of age-, gender-, ethnicity- and village-specific dairy consumption patterns in rural Kazakhstan during the 1950s. Children typically consumed cow's milk with limited consumption of mare, goat and sheep milk; and consumed dairy products such as sour milk (airan), soft cottage cheese (tvorog) and fermented mare milk (koumiss) with the greatest amounts of koumiss reported at ages 15-21 years. The consumption patterns differed by age, and between Kazakh and Russian children, which should lead to different estimates of radiation exposure to the thyroid. This study showed the utility of focus groups to obtain quantitative estimates for dietary intake in the distant past.

Monte Carlo modeling of beta-radiometer device used to measure milk contaminated as a result of the Chernobyl accident.

This paper presents results of Monte Carlo modeling of the beta-radiometer device with Geiger-Mueller detector used in Belarus and Russia to measure the radioactive contamination of milk after the Chernobyl accident. This type of detector, which is not energy selective, measured the total beta-activity of the radionuclide mix. A mathematical model of the beta-radiometer device, namely DP-100, was developed, and the calibration factors for the different radionuclides that might contribute to the milk contamination were calculated. The estimated calibration factors for (131)I, (137)Cs, (134)Cs, (90)Sr, (144)Ce, and (106)Ru reasonably agree with calibration factors determined experimentally. The calculated calibration factors for (132)Te, (132)I, (133)I, (136)Cs, (89)Sr, (103)Ru, (140)Ba, (140)La, and (141)Ce had not been previously determined experimentally. The obtained results allow to derive the activity of specific radionuclides, in particular (131)I, from the results of the total beta-activity measurements in milk. Results of this study are important for the purposes of retrospective dosimetry that uses measurements of radioactivity in environmental samples performed with beta-radiometer devices.