External Gamma Exposure Research Articles

Assessment of natural radioactivity levels and radiation hazard indices for soil samples from Abha, Saudi Arabia

Abstract The natural level of radioactivity in the soil is one of the main causes of external gamma exposure. It was considered necessary to measure concentrations of gamma ray activity due to naturally occurring, potentially hazardous radionuclides from, 226Ra, 232Th and 40K for soil samples collected from different locations (Abha, Khamis Mushait and Muhail Asir) in Asir region. The samples were analyzed for its naturally occurring radionuclides by gamma-ray spectrometry using NaI (Tl). The results show that the average values of activity for 226Ra, 232Th and 40K in range of 38.2 ± 0.1–44.1 ± 0.1, 23.49 ± 0.20–41.9 ± 0.2 and from 182.5 ± 1.0 to 251.5 ± 1.3 Bq Kg−1 respectively. Also the frequency distribution for all radioactive variables in soil was analyzed. Additionally evaluations have been made of the radiological hazards and it's diagramed by Surfer program in maps. These data will serve as the baseline level of radionuclides that occur naturally in the study area and will be useful for tracking and assessing any pollution inventory in the environment of this region.

Cytogenetic damage analysis in mice chronically exposed to low-dose internal tritium beta-particle radiation.

The aim of this study was to carry out a comprehensive examination of potential genotoxic effects of low doses of tritium delivered chronically to mice and to compare these effects to the ones resulting from equivalent doses of gamma-irradiation. Mice were chronically exposed for one or eight months to either tritiated water (HTO) or organically bound tritium (OBT) in drinking water at concentrations of 10 kBq/L, 1 MBq/L or 20 MBq/L. Dose rates of internal β-particle resulting from such tritium treatments were calculated and matching external gamma-exposures were carried out. We measured cytogenetic damage in bone marrow and in peripheral blood lymphocytes (PBLs) and the cumulative tritium doses (0.009 – 181 mGy) were used to evaluate the dose-response of OBT in PBLs, as well as its relative biological effectiveness (RBE). Neither tritium, nor gamma exposures produced genotoxic effects in bone marrow. However, significant increases in chromosome damage rates in PBLs were found as a result of chronic OBT exposures at 1 and 20 M Bq/L, but not at 10 kBq/L. When compared to an external acute gamma-exposure ex vivo, the RBE of OBT for chromosome aberrations induction was evaluated to be significantly higher than 1 at cumulative tritium doses below 10 mGy. Although found non-existent at 10 kBq/L (the WHO limit), the genotoxic potential of low doses of tritium (>10 kBq/L), mainly OBT, may be higher than currently assumed.

Радиационная обстановка на рабочих местах персонала наземных объектов Приаргунского производственного горно-химического объединения

Purpose: To obtain data of radiation survey in workplaces of the personnel of the Priargun Production Mountain Chemical Association (OJSC PPMCA), who work at the premises of the ground facilities. 
 Material and methods: In the course of the radiation survey. Integral track methods were used to measure radon activity concentration by REI-1 track cameras of the TRACK-REI-1M kit. 
 To assess the activity balance factor between radon and its radionuclide progenies, short term measurements of radon activity concentration (AC) and effective equilibrium concentration (EEC) of radon by handle radiometers of radon and its progenies. Gamma dose rate was measured by handle dosimeters.
 Results: Annual AC, EEC and effective dose due to radon and external gamma exposures in workplaces at the ground facilities of OJSC PPMCA have been obtained. Total number of the inspected workshops is 138, including 121 workshops occupied by the A group personnel, and 17 – by the B group personnel. 
 Conclusions: It was shown that annual doses 20 mSv could be exceeded for the A group personnel who work at three workshops shaft 8K of the mine-2, one workshop of building 630A of the Hydro-metallurgical Plant and one workshop of shaft 5 B of G mine.
 In the workshops of the B group personnel, 5 mSv annual effective doses can be exceeded 2 and more times at the premises of canteen number 18 and administrative domestic building of mine-2.

Activity concentrations and dose assessment of 226Ra, 228Ra, 232Th, 40K , 222Rn and 220Rn in soil samples from Newmont-Akyem gold mine using gamma-ray spectrometry

In this study 14 soil samples were measured for natural radioactivity levels including radon-222 (222Rn) and radon-220 (220Rn) concentration at Akyem-Gold Mine premises, surrounding communities in Ghana. Both radon and radioactivity concentrations of radium-226 (226Ra), thorium-232 (232Th) and potassium-40 (40K) were determined by means of gamma spectrometry system equipped with high purity germanium detector. The studied samples gave natural radioactivity levels of 28, 12 and 11 Bq/kg, respectively compared to global 226Ra, 232Th, and 40K concentrations of 37, 33 and 400 Bq/kg, respectively, according to UNSCEAR (2000) report. The annual effective dose rate (AED) due to external and internal gamma exposure ranged from 0.060 to 0.18 mSvy-1 with a mean value of 0.11 ± 0.03 mSvy-1 compared to the recommended value of 1 mSvy-1. There is a correlation between 226Ra and 222Rn in soil gas with a good linear coefficient of (R2 =1). The availability of 226Ra and 222Rn shows that there is a source of uranium-238 (238U) and thorium-232 (232Th) bearing minerals within the adjacent geologic units of Akyem. This implies that most of the radon in the soil gas comes from 226Ra. The assessment of radium equivalent activity varied from 19.71 to 69.88 Bq/kg with mean value of 37.53 ± 15.51 Bq/kg lower than the global limit of 370 Bq/kg. The internal hazard index ranged from 0.07 to 0.25 Bq/Kg with a mean value of 0.13 ± 0.05 Bq/Kg, also lower than the accepted value of unity, while external hazard index ranged from 0.05 to 0.19 Bq/Kg with a mean value of 0.10 ± 0.04 Bq/Kg. Key words: Radon, thoron, natural radioactivity, annual effective dose, radium equivalent index, external and internal hazard index.

Радиационный риск заболеваемости гипертензиями среди российских участников ликвидации аварии на Чернобыльской АЭС

Purpose: The main purpose of the research is to define the group of radiation risk (GRR) on the incidence of hypertension among Russian recovery operation workers of the Chernobyl accident (liquidators).
 Material and methods: The object of research is the cohort of the Russian liquidators with the known individual doses of external gamma exposure of all body. Definition of GRR on incidence of hypertension is based on assessment of excess relative radiation risk (ERR) and relative radiation risk (RR) in the observed cohort of 106 thousand liquidators, having average accumulated dose of external gamma exposure of all body of 0.11 Gy and the maximum individual doses about 1 Gy.
 Results: From 1986 to 2012 in this cohort 57112 cases of hypertension have been diagnosed, basically – essential (primary) hypertension (39.2 %) and hypertensive heart disease (53.8 %). The statistically significant ERR of incidence of hypertension was observed only for liquidators who entered the Chernobyl zone of recovery operations within the first year after the accident (before 26.04.1987): ERR/Gy = 0.26 with 95 % CI (0.12; 0.41), p < 0.001. For other liquidators no significant associations between the explosion dose and the incidence of hypertension were revealed. For nonparametric estimates of RR in dose groups (relative to the control group with doses < 0.05 Gy) the statistically significant radiation risk was observed only for the dose group over 0,25 Gy: RR = 1.07 at 95 % of CI (1.02; 1.12), p = 0.023. GRR on incidence of hypertension equal to 4 % of the number of the studied cohort of liquidators: 4515 persons with accumulated doses of 0.25 Gy and higher, arrived to the Chernobyl area within the first year after the accident. In GRR 2597 cases of diseases of hypertension were diagnosed; statistically significant (p = 0.023) assessment of RR is equal 1.07, with 95 % a confidential interval (1.02; 1.12) and an average dose 0.297 Gy. During observation from 1986 to 2012 6.5 % of cases of diseases of hypertension (170 cases) in GRR can be related to radiation-caused ones. GRR for the beginning of 2013 consisted of 2919 persons 1909 of whom had already had diagnoses of hypertension (125 – radiation caused). Since 2013 for lifetime in GRR from 43 to 66 cases of diseases of hypertension which can be related to radiation-caused are expected.
 Conclusion: As hypertension is the risk factor for many circulatory diseases, address prevention and treatment of hypertension in GRR in the first years after radiation accidents could reduce the radiation-caused loss healthy years of participants of elimination of such accidents.

Radiological dose in Muria peninsula from SB-LOCA event

Dose assessment for accident condition is performed for Muria Peninsula region using source-term from Three-Mile Island unit 2 SB-LOCA accident. Xe-133, Kr-88, 1-131 and Cs-137 isotopes are considered in the calculation. The effluent is assumed to be released from a 50 m stack. Lagrangian particle dispersion method (LPDM) employing non-Gaussian dispersion coefficient in 3-dimensional mass-consistent wind-field is employed to obtain periodic surface-level concentration which is then time-integrated to obtain spatial distribution of ground-level dose. In 1-hour simulation, segmented plumes with 60 seconds duration with a total of 18.000 particles involved. Simulations using 6-hour worst-case meteorological data from Muria peninsula results in a peak external dose of around 1.668 mSv for low scenario and 6.892 mSv for high scenario in dry condition. In wet condition with 5 mm/hour and 10 mm/hour rain for the whole duration of the simulation provides only minor effect to dose. The peak external dose is below the regulatory limit of 50 mSv for effective skin dose from external gamma exposure.

Reconstruction of individualized doses of subjects from the Ukrainian State Register – of Persons that Affected due to Chornobyl accident and reside in Korosten raion of Zhytomyr oblast

To elaborate an ecological dosimetric model of reconstruction individualized exposure doses of subjects from the State Register of Ukraine (SRU) - of persons, affected due to Chornobyl accident and reside at the radioactive contaminated territory of Korosten raion of Zhytomyr Oblast, and to calculate exposure doses for those persons. In the paper, an ecological dosimetric model is presented which is elaborated in order to individualize exposure doses of people who reside in Korosten raion of Zhytomyr Oblast and are registered in SRU. The model is based on the results of radio ecological and dosimetric monitoring held in the period of 1986-2013 at the territory of northern oblasts of Ukraine. Annual dose over each post accidental year consists of the two compo nents: (a) annual effective dose of external gamma exposure (due to radioactive fallout on the ground), and (b) internal exposure of the whole body (due to consumption of meal contaminated by radioactive isotopes). For 1986, the dose of internal exposure is evaluated out of all main radionuclides of radioactive accidental fallout, and after 1987 only for radioisotopes of caesium (134Cs and 137Cs). The parameterization of the model is based on the pre vious experience in working out a complex of ecological dosimetric models for estimation of referent exposure doses of Ukrainian population. Individualized doses of external and internal exposure (annual and accumulated) are estimated for the population of various age groups that resides in the settlements of Korosten raion (totally about 100 settlements). Separately the doses are presented for rural settlements of the raion and for the city of Korosten for each year of the post accidental period of 1986-2016. Estimates of doses are given that were accumulated: (a) during 15 years just after the accident, (b) for the period of 2000-2016, and (c) for 30 year period after the acci dent. Mean dose accumulated for 30 years after the Chornobyl accident by residents of rural settlements of Korosten raion is estimated as 19.8 mSv, and for inhabitants of the Korosten city as 20.9 mSv. On condition of permanent res idence in the raion, residents of about 66 % settlements of Korosten raion accumulated the doses in the interval 5 20 mSv during 30 years after the accident. For the residents of about 25 % settlements the accumulated dose is in the interval 20-50 mSv, and for 7 % of settlements it exceeds 50 mSv.

A study of thoron exhalation from monazite-rich beach sands of High Background Radiation Areas of Kerala and Odisha, India

Thoron exhalation from earth’s surface is the most important source of environmental thoron. The High Background Radiation Areas (HBRAs) of Kerala and Odisha in India have beaches with sands enriched with monazite, an ore of thorium, making it unique for study of thoron exhalation. In the present study, in situ measurement of thoron exhalation was carried out to map the thoron exhalation rate over complete coastline of the known HBRAs. New experimental setups for measurement of thoron surface exhalation and thoron mass emanation were developed and validated. The exhalation measurements were carried out on beaches of Chavara–Neendakara (CN) area of Kerala and Chatrapur (CH) region of Odisha. The beaches of the Kerala region showed an average thoron exhalation rate of 5.95 ± 2.98 Bq m−2s−1, which for the beaches of Chatrapur area of Odisha was 2.77 ± 0.96 Bq m−2s−1. The external gamma exposure rate was also measured at these locations, and it was observed to be well correlated with in situ thoron exhalation rate. Sand samples were collected from ten of the measurement locations and analyzed in the laboratory for a further understanding of thoron exhalation process in the beach sand. Measurement of specific thoron mass emanation rate, specific 224Ra content and thoron emanation coefficient was taken for the samples. A good correlation was found between in situ thoron exhalation rate and specific thoron mass emanation rate. The effective thoron diffusion length was determined by using the measured parameters in the UNSCEAR radon exhalation model and was found to be nearly constant with a value of 2.2 ± 0.36 cm. This study shows that in spite of very high thorium content (500–1000 times) as compared to normal fine soils, the thoron exhalation from the HBRA beach sands was only 4–12 times higher due to very low emanation coefficient, about 1000 times smaller than that for normal soils.

Estimates of Radiation Effects on Cancer Risks in the Mayak Worker, Techa River and Atomic Bomb Survivor Studies.

For almost 50 y, the Life Span Study cohort of atomic bomb survivor studies has been the primary source of the quantitative estimates of cancer and non-cancer risks that form the basis of international radiation protection standards. However, the long-term follow-up and extensive individual dose reconstruction for the Russian Mayak worker cohort (MWC) and Techa River cohort (TRC) are providing quantitative information about radiation effects on cancer risks that complement the atomic bomb survivor-based risk estimates. The MWC, which includes ~26 000 men and women who began working at Mayak between 1948 and 1982, is the primary source for estimates of the effects of plutonium on cancer risks and also provides information on the effects of low-dose rate external gamma exposures. The TRC consists of ~30 000 men and women of all ages who received low-dose-rate, low-dose exposures as a consequence of Mayak's release of radioactive material into the Techa River. The TRC data are of interest because the exposures are broadly similar to those experienced by populations exposed as a consequence of nuclear accidents such as Chernobyl. In this presentation, it is described the strengths and limitations of these three cohorts, outline and compare recent solid cancer and leukemia risk estimates and discussed why information from the Mayak and Techa River studies might play a role in the development and refinement of the radiation risk estimates that form the basis for radiation protection standards.

Effective Doses of Employees at the Former Uranium Processing Plant MAPE Mydlovary, Czechoslovakia

Results are presented of a survey of almost 1000 dosimetric records of employees at the former uranium processing plant MAPE Mydlovary. Located ~20 km to the north-west of České Budějovice in South Bohemia, it was the place where most of the uranium ore mined in Czechoslovakia in the years from 1962 to 1991 was processed. The records refer to incorporation of short-lived radon progeny and long-lived radionuclides as well as external gamma exposure. The average annual doses calculated from the recorded data were 2.7±1.4, 5.0±3.1 and 1.7±0.9 mSv from these three sources, respectively. Thus, the relative contributions of these components to the effective dose were 29±6, 53±14 and 18±13% , respectively. This is different from the findings in an earlier study for the exposure of uranium miners, where the overall doses were similar, but over 50% was contributed by short-lived radon progeny. No legal limits applicable at the time were exceeded, as the inclusion of long-lived radionuclides in the dose calculations was not yet obligatory.

Radiation Risks of Leukemia, Lymphoma and Multiple Myeloma Incidence in the Mayak Cohort: 1948-2004.

Incidence of all types of lymphatic and hematopoietic cancers, including Hodgkin’s lymphoma, non-Hodgkin's lymphoma, multiple myeloma, acute and chronic myeloid leukemia (AML and CML respectively), chronic lymphocytic leukemia (CLL) and other forms of leukemia have been studied in a cohort of 22,373 workers employed at the Mayak Production Association (PA) main facilities during 536,126 person-years of follow-up from the start of employment between 1948 and 1982 to the end of 2004. Risk assessment was performed for both external gamma-radiation and internal alpha-exposure of red bone marrow due to incorporated Pu-239 using Mayak Workers Dosimetry System 2008 taking into account non-radiation factors. The incidence of leukemia excluding CLL showed a non-linear dose response relationship for external gamma exposure with exponential effect modifiers based on time since exposure and age at exposure. Among the major subtypes of leukemia, the excess risk of AML was the highest within the first 2–5 years of external exposure (ERR per Gy: 38.40; 90% CI: 13.92–121.4) and decreased substantially thereafter, but the risks remained statistically significant (ERR per Gy: 2.63; 90% CI: 0.07–12.55). In comparison, excess CML first occurred 5 years after exposure and decreased about 10 years after exposure, although the association was not statistically significant (ERR per Gy: 1.39; 90% CI: -0.22–7.32). The study found no evidence of an association between leukemia and occupational exposure to internal plutonium ERR per Gy 2.13; 90% CI: <0–9.45). There was also no indication of any relationship with either external gamma or internal plutonium radiation exposure for either incidence of Hodgkin or non-Hodgkin lymphoma or multiple myeloma.

Relative biological effectiveness of alpha particles at radon exposure.

The relative biological effectiveness (RBE) of alpha particles at radon exposure is estimated by comparison of radiation risks at external gamma exposure and radon exposure in different situations. For external gamma exposure, the BEIR VII model of radiation risk assessment was used. For occupational and indoor radon exposure, models such as BEIR VI, WISMUT, Tomasek's and combined miners population were considered. It was demonstrated that RBE values are strongly dependent on models of radiation risk assessment used for RBE calculation, sex of exposed peoples and age at the exposure. The average values of RBE in dependence on model of risk assessment choice are in the range from 1.5 to 12.0 for males and in the range from 0.34 to 2.7 for females.

Assessment of radon concentration and external gamma radiation level around a high background radiation area (HBRA), Odisha, India and its radiological significance

Present study gives a brief account of the atmospheric radon concentration, gamma absorbed dose rate and radiation dose received by the members of public residing in a coastal HBRA, Chatrapur, Odisha, India. The external gamma radiation dose varies from 40 to 1800 nSv/h, averaged by 226 nSv/h. The total average effective dose rate received by members of public from inhalation of radon and its progeny and external gamma exposure was estimated to be 4 ± 1.0 mSv/y, ranged between 2.4 and 6.3 mSv/y, which is nearly two higher than the global average value of effective dose to public due to natural radiation exposure.

Radiation effects on mortality from solid cancers other than lung, liver, and bone cancer in the Mayak worker cohort: 1948-2008.

Radiation effects on mortality from solid cancers other than lung, liver, and bone cancer in the Mayak worker cohort: 1948–2008. The cohort of Mayak Production Association (PA) workers in Russia offers a unique opportunity to study the effects of prolonged low dose rate external gamma exposures and exposure to plutonium in a working age population. We examined radiation effects on the risk of mortality from solid cancers excluding sites of primary plutonium deposition (lung, liver, and bone surface) among 25,757 workers who were first employed in 1948–1982. During the period 1948–2008, there were 1,825 deaths from cancers other than lung, liver and bone. Using colon dose as a representative external dose, a linear dose response model described the data well. The excess relative risk per Gray for external gamma exposure was 0.16 (95% CI: 0.07 – 0.26) when unadjusted for plutonium exposure and 0.12 (95% CI 0.03 – 0.21) when adjusted for plutonium dose and monitoring status. There was no significant effect modification by sex or attained age. Plutonium exposure was not significantly associated with the group of cancers analyzed after adjusting for monitoring status. Site-specific risks were uncertainly estimated but positive for 13 of the 15 sites evaluated with a statistically significant estimate only for esophageal cancer. Comparison with estimates based on the acute exposures in atomic bomb survivors suggests that the excess relative risk per Gray for prolonged external exposure in Mayak workers may be lower than that for acute exposure but, given the uncertainties, the possibility of equal effects cannot be dismissed.

Public effective doses from environmental natural gamma exposures indoors and outdoors in Iran.

The effective doses of public in Iran due to external gamma exposures from terrestrial radionuclides and from cosmic radiation indoors and outdoors of normal natural background radiation areas were determined by measurements and by calculations. For direct measurements, three measurement methods were used including a NaI(TI) scintillation survey meter for preliminary screening, a pressurised ionising chamber for more precise measurements and early warning measurement equipment systems. Measurements were carried out in a large number of locations indoors and outdoors ∼1000 houses selected randomly in 36 large cities of Iran. The external gamma doses of public from living indoors and outdoors were also calculated based on the radioactivity measurements of samples taken from soil and building materials by gamma spectrometry using a high-resolution HPGe system. The national mean background gamma dose rates in air indoors and outdoors based on measurements are 126.9±24.3 and 111.7±17.72 nGy h(-1), respectively. When the contribution from cosmic rays was excluded, the values indoors and outdoors are 109.2±20.2 and 70.2±20.59.4 nGy h(-1), respectively. The dose rates determined for indoors and outdoors by calculations are 101.5±9.2 and 72.2±9.4 nGy h(-1), respectively, which are in good agreement with directly measured dose rates within statistical variations. By considering a population-weighted mean for terrestrial radiation, the ratio of indoor to outdoor dose rates is 1.55. The mean annual effective dose of each individual member of the public from terrestrial radionuclides and cosmic radiation, indoors and outdoors, is 0.86±0.16 mSv y(-1) by measurements and 0.8±0.2 mSv y(-1) by calculations. The results of this national survey of public annual effective doses from national natural background external gamma radiation determined by measurements and calculations indoors and outdoors of 1000 houses in 36 cities of Iran are presented and discussed.

Independent validation of candidate genes identified after a whole genome screening on Mayak workers exposed to prolonged occupational radiation.

We evaluated gene expression in the peripheral blood of Mayak workers in relationship to occupational chronic exposure to identify permanent post-exposure signatures. The Mayak workers had experienced either a combined exposure to incorporated (239)Pu and external gamma rays (n = 82) or exposure to external gamma rays (n = 18). Fifty unexposed individuals served as controls. Peripheral blood was collected and then the RNA was isolated, converting it into cDNA and stored at -20°C. In a previous study at stage I, we screened the mRNA and microRNA transcriptome using 40 of the 150 samples and identified 95 mRNAs and 45 microRNAs. In stage II of this study, we now validated our 140 candidate genes using the qRT-PCR technique for the remaining 92 blood samples (18 samples were lost due to methodological reasons). We analyzed associations of normalized gene expression values in linear models separately for both exposure types (continuous and categorical scales) and adjusted for exposure age as well as stratified by gender. After further adjustment for confounders such as chronic non-cancer diseases or age at biosampling, mostly binary (on/off) dose-to-gene relationships were found for 15 mRNAs and 15 microRNAs, of which 8 mRNAs and 6 microRNAs remained significant after Bonferroni correction. Almost all of them were associated with plutonium incorporation and gender. Our study provides mRNA and microRNA gene expression changes dependent on the exposure type and gender, which occur and seem to persist after chronic radiation exposures supporting the concept of permanent post-exposure signatures.

Assessment of radon concentration and external gamma radiation level in the environs of the proposed uranium mine at Peddagattu and Seripally regions, Andhra Pradesh, India

In the environs of uranium mineralized terrain, a little higher ambient radon concentration and airborne gamma radiation level may be expected in comparison with natural background. It is necessary to determine the radon concentration and gamma radiation level in comparison with natural background radiation for future control or to minimize the health risks. The present study gives a brief account of atmospheric radon concentration, gamma absorbed dose rate and radiation dose received by the members of public in the vicinity of the proposed uranium mine area of Nalgonda district, Andhra Pradesh, India. The ambient radon concentration in the air in the study area was found to vary from 1.74 to 25.6 Bq m−3 with geometric mean of 8.88 Bq m−3 and geometric standard deviation of 1.75 Bq m−3. The measured gamma absorbed dose rate in air at 1 m above the ground ranged from 4.6 to 29.8 μR h−1 with an overall arithmetic mean of 16.63 ± 1.39 μR h−1. The mean annual effective dose received by the members of public from inhalation of radon and its progeny and external gamma exposure was estimated to be 0.23 mSv year−1, which is falling well under the annual effective dose limit of 1 mSv year−1 recommended by ICRP.

Gamma dose rate due to natural and manmade radiation sources from a nuclear facility in Mexico

The environmental external gamma dose rate has been determined at the Mexican Nuclear Research Centre and surrounding communities, located in a forest area. Outdoor direct measurements of external gamma exposure and absorbed dose rates in air were performed using passive integrating thermoluminescent dosimeters. Radiological measurements were also carried out with a portable high pressure ionization chamber. The gamma dose rate was evaluated from data obtained along 10 years measurements. The activity concentrations of 40K, 226Ra, 232Th, 137Cs, and 235U in surface soil samples at sampling sites are also presented. The radionuclide activity concentrations were determined by low background gamma spectrometry with hyper-pure germanium detectors. A site specific lineal model to describe the relationship between the external gamma dose rate and the 226Ra concentration values in the soil is proposed.

Determination of dose rate from Chernobyl-derived radiocaesium in Estonian soil

The deposition and vertical depth distribution of 134Cs and 137Cs in the natural undisturbed soil profiles down to 20–25 cm were studied at locations in the North Eastern Estonia, which were most strongly affected by the Chernobyl fallout in 1986. The total depositions were estimated based on summing the sampled and measured activities of 134Cs and 137Cs in all sections of soil profiles. The Chernobyl 137Cs deposition values varied considerably from site to site and the range was from 3.9 kBq m−2 to 50.2 kBq m−2, with the average of 22.8 kBq m−2 for the region (reference data May 1, 1986). The ratio of total activities, A(134Cs)/A(137Cs), varied in the range from 0.47 to 0.55. Using a compartment model and the observed data on the 134Cs and 137Cs activity concentrations (Bq m−2) in four compartments, 0–1 cm, 1–5 cm, 5–15 cm and 15–30 cm, of soil collected in 1991–2003, the approximate residence half-times of radiocaesium in soil were determined. The latter increased from 3.7 y in the top-most compartment to 8.6 y and 36.4 y in the deeper compartments, respectively. The time dependence of the external gamma-dose rate at the height of 1 m above a flat ground area arising from the deposited and migrating radiocaesium was calculated using the modeled data on the 134Cs and 137Cs activity in soil compartments. Considering the total depositions of radiocaesium in soil from the Chernobyl 1986 accident, the 50 year effective doses caused by external gamma exposure varied in the range from 0.13 mSv to 1.74 mSv, with the mean of 0.79 mSv in the region.

Assessment of radon concentration and external gamma radiation level in the environs of Narwapahar uranium mine, India and its radiological significance

In the environs of uranium mining, milling and processing facilities and in the uranium mineralized terrain, a little higher ambient radon concentration and gamma radiation level may be expected in comparison with natural background. The present study gives a brief account of atmospheric radon concentration, gamma absorbed dose rate and radiation dose received by the members of public in the vicinity of Narwapahar uranium mine. The ambient radon concentration in the air in the study area was found to vary from 5 to 107 Bq m−3 with geometric mean of 24 Bq m−3 and geometric standard deviation of 1.74 Bq m−3. The measured gamma absorbed dose rate in air at 1 m above the ground ranged from 87 to 220 nGy h−1 with an overall arithmetic mean of 128 ± 18.5 nGy h−1. The mean annual effective dose received by the members of public from inhalation of radon and its progeny and external gamma exposure was estimated to be 0.32 mSv year−1, which is comparable to other reported values elsewhere.