Average Effective Dose Rate Research Articles

Assessment of environmental radioactivity concentration and effective dose rates from radon gas exposure from water samples in Gezira State, Sudan

A study was conducted in Gezira State, Sudan, to estimate the concentration of radon and the annual effective dose rate in water samples based on inhalation, ingestion, and age group. The study collected 26 samples from different locations. The results showed that the mean concentration of radon was 7.68 ± 1.07 Bq.l−1, and the mean effective dose rate of radon released from water to indoor air was 19.17 ± 2.68 μSv.y−1. The average effective dose rates calculated from ingestion, inhalation, and the total annual effective dose rate were 18.81 ± 2.63, 19.34 ± 2.71, and 38.15 ± 5.34 μSv.y−1, respectively. The annual effective dose rates for infants, children, and adults were calculated to have mean values of 80.60 ± 11.27, 53.73 ± 7.51, and 38.38 ± 5.37 μSv.y−1, respectively. The study found that 23.1% of the samples exceeded the maximum contamination level, while 76.9% were below the reference levels set by the USEPA, WHO, and EU. Despite the increase in radiation dose with age and consumption rates, the radiation dose from water was lower than the recommended limits set by UNSCEAR and WHO. Additionally, the bronchial epithelium received twice the radiation dose compared to the stomach walls.

Automated Workflow for Calculating the Collective and Average Effective Doses of Galactic Cosmic Radiation Received by Pilots in Taiwan from 2006 to 2021.

On the basis of statistical data obtained from publicly available annual civil aviation reports, we developed an automated workflow for estimating the overall radiation exposure of aircraft pilots caused by galactic cosmic radiation. The workflow comprises several data-processing scripts that work with the batch analysis capability built in the NTHU Flight Dose Calculator . This method can quickly provide best possible estimates of the annual collective and average effective doses received by pilots of various airlines because all passenger, cargo, and charter flights operated that year were considered rather than some selected flights. The workflow and its implementation as well as analysis of results for the period of 2006-2021 are discussed herein. The results revealed that in 2019, six airlines in Taiwan operated 479 separate flight segments with 226 aircraft. The collective effective dose received by all 2,986 pilots was approximately 5,536 person-mSv; hence, the average individual effective dose was 1.85 mSv. During the COVID-19 pandemic, the doses decreased by more than half. In 2020, the collective effective dose received by all 2,936 pilots decreased sharply to 2,527 person-mSv, corresponding to an average effective dose per pilot of only 0.86 mSv. During 2006-2019, the annual average effective dose per pilot in Taiwan was between 1.65 and 2.71 mSv, and the average effective dose rate per flight hour was 3.15 μSv h. -1.

Radiation Aspect of Two Orbit Inclination Options of the Russian Orbital Service Station

The contribution to the effective dose from cosmic radiation of the Earth’s radiation belts, galactic cosmic rays, and solar proton events for astronauts located in the large-diameter working compartment of the service module of the ISS is considered. It is shown that for quasi-stationary sources of cosmic radiation, a change in the orbital inclination of 51.6° by 97.0° does not lead to significant variations in the average daily effective dose rate. When considering the contribution to the effective dose from solar-flare protons, the dose load on astronauts can increase by ten or more times.

High Environmental Radioactivity in Artisanal and Small-Scale Gold Mining in Eastern Democratic Republic of the Congo

The radioactivity associated with artisanal and small-scale gold mining activities (ASM) carried out along the Ulindi River, in the eastern Democratic Republic of the Congo, was evaluated by gamma-ray spectrometry and inductively coupled plasma–mass spectrometry of soil and sediment samples. The results revealed that activity concentrations of 238U (up to 3127 ± 98 Bq kg−1), 226Ra (up to 2710 ± 89 Bq kg−1) and 232Th (up to 2142 ± 162 Bq kg−1) were 71- to 89-fold higher than the worldwide average concentrations reported by UNSCEAR in soils. Primordial radionuclides are, thus, present in high concentrations in deposits of gold in that region and the average ambient effective radiation dose rate was determined at 8.4 mSv y−1 (range 0.5 to 40 mSv y−1). This area may be classified as a natural high background radiation area (HBRA). The radiation risk for artisanal miners and population members manipulating those geological materials were assessed through radiological parameters. such as the radium equivalent activity index (RaEq), outdoor gamma absorbed dose rate (ODRA), annual effective dose equivalent (AEDE), and excess lifetime cancer risk (ELCR). The mean values of these parameters were significantly elevated in comparison to the world average levels and indicated the existence of significant radiation risks for gold miners and members of the local population. A radiation safety policy seems needed to protect workers and the local population in this region.

Determination of Activity Concentration of Natural Radionuclides and Radiation Hazards' Assessment of Building Materials in High Background Radiation Areas of Homa and Ruri, Kenya.

The areas around Homa and Ruri hills in Homa Bay County in Kenya are associated with high background radiation levels. The activity concentration of the natural radionuclides (226Ra, 232Th, and 40K) in earthen building materials used in the areas of Homa and Ruri hills has been measured using a NaI (Tl) detector in this work. The measured values of radioactivity concentrations are used to estimate the associated radiological risk. The earthen building material samples from Ruri registered relatively high 232Th concentration values averaging 1094 ± 55 Bq/kg, nearly three times those of the samples from Homa. 226Ra level was not significantly different in both regions with Homa reporting 129 ± 10 Bq/kg and Ruri 111 ± 6 Bq/kg. 40K was however higher in the samples from Homa by an approximate factor of 2 relative to those from Ruri where the activity concentration was 489 ± 24 Bq/kg. The radium equivalents for 226Ra, 232Th, and 40K in the samples from Ruri were 111 ± 9, 1564 ± 125, and 38 ± 3 Bq/kg, while in Homa, the values were 129 ± 10, 570 ± 46, and 69 ± 5 Bq/kg, respectively. The calculated value of total radium equivalent in Ruri was 1713 ± 137 Bq/kg which was two times higher than that of Homa. 232Th contributed about 74% and 91% to the total radium equivalent in Homa and Ruri, respectively; thus, it was the one with the largest contribution to radiation exposure in both regions. The average indoor annual effective dose rates were 1.74 ± 0.14 and 3.78 ± 0.30 mSv/y in Homa and Ruri, respectively, both of which were above the recommended safety limit of 1 mSv/y.

Occupational radiation dose for medical workers at the University Hospital Center “Mother Theresa” in Tirana

The exposure to environmental and “artificial” radiation sources was investigated in the University Hospital Center “Mother Theresa” in Tirana. The concentration of indoor radon exceeds the reference level of 300 Bq m−3 in some 50% of workplaces, accounting for an average effective dose rate of 3.7 mSv y−1. The average dose rate due to external gamma radiation was measured to be 0.12 mSv y−1. While, the occupational exposure of medical workers was found to be 0.67 mSv y−1 on average. The high radon concentrations account for approximately 83% of worker radiation dose, indicating the need for adopting mitigation actions.

Dose rate in the highest irradiation area of the rectum correlates with late rectal complications in patients treated with high-dose-rate computed tomography-based image-guided brachytherapy for cervical cancer.

The purpose of this study was to evaluate the effect of dose rate to the rectum on late rectal complications in patients treated with computed tomography (CT)-based image-guided brachytherapy (IGBT) for cervical cancer. The subjects were 142 patients with cervical cancer who underwent Ir-192 high-dose-rate (HDR)-IGBT between March 2012 and January 2018. The dose rate to the rectum was calculated using in-house software. The minimum, mean and maximum effective dose rate (EDR) was calculated for voxels of the rectal volume covered by cumulative doses >D0.1cc, >D2cc, and > D5cc. The average EDR of three to four brachytherapy sessions was calculated (EDR for patients; EDRp). The total dose of the rectum was calculated as the biologically equivalent dose in 2-Gy fractions (EQD2). The associations between EDRp for D0.1cc, D2cc, and D5cc and the respective rectal EQD2 values with late rectal complications were then analyzed. The median follow-up period was 40 months. Patients with rectal complications of ≥Grade 1 received a significantly higher mean EDRp for D0.1cc–5cc and had a greater EQD2 for D0.1cc–5cc. Multivariate analysis was performed using the mean EDRp for D2cc, EQD2 for D2cc, heavy smoking and BMI. Of these four variables, mean EDRp for D2cc (HR = 3.38, p = 0.004) and EQD2 for D2cc (HR = 2.59, p = 0.045) emerged as independent predictors for late rectal complications. In conclusion, mean EDRp and EQD2 were associated with late rectal complications in patients treated with HDR CT-based IGBT for cervical cancer.

Assessment of Indoor Radon Concentration in Residential Buildings at Ouagadougou and Estimation of the Annual Effective Dose

The second most important cause of lung cancer after smoking is a radon gas. Thus, the determination of indoor radon concentrations in residential buildings is an important public health concern. The purpose of this research was to measure the concentration of radon gas in residential homes in the city of Ouagadougou and evaluate the annual effective dose, effective dose equivalent and the relative risk of lung cancer. The present study used the digital radon detector air things of cranium to determine the concentration of radon in twenty one homes at Ouagadougou. The digital radon detector air Things of corentium was placed in each residential building for a minimum period of one week and the concentration values are read every 24 hours. The values recorded are the short term average and the long term average. This study showed that the average radon concentration was 26.90±2.58 Bq/m³ in residential homes at Ouagadougou. The average radon effective dose rate was calculated as 0.68 mSv per year and the average effective dose equivalent of 1.63 mSv per year. The average relative risk of lung cancer (RRLC) due to indoor exposure was 1.02. The concentration of radon in one house was found to be greater than 100 Bq/m³, which is above the level allowed by the World Health Organization (WHO). The radon Effective Dose Equivalent in 14.3% of homes were slightly larger than the limit of the recommended action level (3-10 mSv per year) as reported by the ICRP-1993. It seems necessary to increase the public’s awareness of this issue and to take action to reduce radon in homes when the concentrations are above.

A Comprehensive Approach for Estimating Collective and Average Effective Doses of Galactic Cosmic Radiation Received by Pilots.

This study proposes a feasible and comprehensive approach for estimating collective and average effective doses of galactic cosmic radiation received by pilots on the basis of data in publicly available civil aviation annual statistical reports. Large uncertainties are associated with the estimation of these quantities because the radiation environment at aviation altitudes is complex, and a large number of flights operated by various air carriers is involved. A best estimate can be obtained through this approach because it considers all passenger, cargo, and charter flights operated during a long period of time instead of subjectively selecting some representative flights for dose evaluation. The approach becomes feasible and practical with the aid of a special feature called automatic batch analysis in the NTHU Flight Dose Calculator. There are two international airlines in Taiwan: China Airlines and EVA Air. As a demonstration, the collective effective dose received by the 2,513 pilots from the two airlines in 2018 was estimated to be 4,947 person-mSv, and the average effective dose per pilot was 1.97 mSv. These estimates were considered representative because they were based on all 151,526 flight segments operated that year. The assessment of the annual effective doses received by pilots in Taiwan from 2006 to 2018 was performed. The results varied in the range of 1.70-2.97 mSv because of variations in solar activity and operational flight routes. A regression model that can effectively reproduce the derived average effective dose rates on board aircraft was obtained for future application in aircrew dosimetry.

A Radiological Survey in Tailings: A Case Study of Rosterman Gold Mine, Western Kenya

Thirty samples of tailing waste weighing 200 g were randomly collected from both active and inactive tunnels at the Rosterman gold mine site in western Kenya. The average activity concentration of the radionuclides (40K, 232Th and 238U) analyzed by the gamma-ray spectrometry in the tailing samples was 260 ± 14.29 Bq/Kg for 40K, 118 ± 8.25 Bq/Kg for 232Th and 81 ± 3.63 Bq/Kg for 238U. The corresponding radiological parameters for all the collected thirty tailing waste samples were determined from the specific mean activity concentrations. The average dose rate for all the samples was 54 nGy/h. The average radium equivalent value was 262 ± 12.04 Bq/Kg with a range of 154 ± 6.42 Bq/Kg to 350 ± 10.24 Bq/Kg. The average values of external and internal indices were 0.6 ± 0.03 mSv/y and 0.7 ± 0.04 mSv/y respectively. The average indoor and outdoor annual effective dose rates that were determined for this study were 0.3 ± 0.02 and 0.2 ± 0.01 respectively. Therefore, the tailing samples recorded doses and radiological indices below the world average permissible values. This implies that the radiation exposure to the miners and general public due to tailing wastes at Rosterman gold mine poses no significant health risk.

Doğu Karadeniz Bölgesinde kozmik ışın kaynaklı yıllık etkin doz dağılımının belirlenmesi

In this study, annual effective dose rate distribution due to cosmic radiation, which constitutes an important part of natural radiation, was mapped in spatial pixels for three provinces in the Eastern Black Sea region (Artvin, Rize and Trabzon). Cosmic ray-induced annual effective dose calculations were performed based on latitude and altitude changes with EXPACS, an excel-based program. Besides, the effect of cosmic radiation on the population living in the study area was determined. For the entire study area, it was calculated the average effective dose rate from Cosmic radiation as 0.65 mSv y-1 and range as (0.33-1.72) mSv y-1. The average annual collective effective dose rate was determined approximately 508 person-Sv y-1. Besides, the population-weighted average annual effective dose rates were obtained as 449, 376 and 370 for Artvin, Rize and Trabzon provinces, respectively.

Assessment of background gamma radiation levels using airborne gamma ray spectrometer data over uranium deposits, Cuddapah Basin, India – A comparative study of dose rates estimated by AGRS and PGRS

The Atomic Minerals Directorate for Exploration and Research (AMD) has conducted high-resolution airborne gamma ray spectrometer (AGRS), magnetometer and time domain electromagnetic (TDEM) surveys for uranium exploration, along the northern margins of Cuddapah Basin. The survey area includes well known uranium deposits such as Lambapur-Peddagattu, Chitrial and Koppunuru. The AGRS data collected for uranium exploration is utilised for estimating the average absorbed rates in air due to radio-elemental (potassium in %, uranium and thorium in ppm) distribution over these known deposit areas. Further, portable gamma ray spectrometer (PGRS) was used to acquire data over two nearby locations one from Lambapur deposit, and the other from known anomalous zone and subsequently average gamma dose rates were estimated. Representative in-situ rock samples were also collected from these two areas and subjected to radio-elemental concentration analysis by gamma ray spectrometer (GRS) in the laboratory and then dose rates were estimated. Analyses of these three sets of results complement one another, thereby providing a comprehensive picture of the radiation environment over these deposits. The average absorbed area wise dose rate level is estimated to be 130 ± 47 nGy h−1 in Lambapur-Peddagattu, 186 ± 77 nGy h−1 in Chitrial and 63 ± 22 nGy h−1 in Koppunuru. The obtained average dose levels are found to be higher than the world average value of 54 nGy h−1. The gamma absorbed dose rates in nGy h−1 were converted to annual effective dose rates in mSv y−1 as proposed by the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR). The annual average effective dose rates for the entire surveyed area is 0.12 mSv y−1, which is much lower than the recommended limit of 1 mSv y−1 by International Commission on Radiation protection (ICRP). It may be ascertained here that the present study establishes a reference data set (baseline) in these areas to assess any changes in gamma radiation levels due to mining and milling activities in future.

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.

Respiratory motion management using audio-visual biofeedback for respiratory-gated radiotherapy of synchrotron-based pulsed heavy-ion beam delivery.

To efficiently deliver respiratory-gated radiation during synchrotron-based pulsed heavy-ion radiotherapy, a novel respiratory guidance method combining a personalized audio-visual biofeedback (BFB) system, breath hold (BH), and synchrotron-based gating was designed to help patients synchronize their respiratory patterns with synchrotron pulses and to overcome typical limitations such as low efficiency, residual motion, and discomfort. In-house software was developed to acquire body surface marker positions and display BFB, gating signals, and real-time beam profiles on a LED screen. Patients were prompted to perform short BHs or short deep breath holds (SDBH) with the aid of BFB following a personalized standard BH/SDBH (stBH/stSDBH) guiding curve or their own representative BH/SDBH (reBH/reSDBH) guiding curve. A practical simulation was performed for a group of 15 volunteers to evaluate the feasibility and effectiveness of this method. Effective dose rates (EDRs), mean absolute errors between the guiding curves and the measured curves, and mean absolute deviations of the measured curves were obtained within 10%-50% duty cycles (DCs) that were synchronized with the synchrotron's flat-top phase. All maneuvers for an individual volunteer took approximately half an hour, and no one experienced discomfort during the maneuvers. Using the respiratory guidance methods, the magnitude of residual motion was almost ten times less than during nongated irradiation, and increases in the average effective dose rate by factors of 2.39-4.65, 2.39-4.59, 1.73-3.50, and 1.73-3.55 for the stBH, reBH, stSDBH, and reSDBH guiding maneuvers, respectively, were observed in contrast with conventional free breathing-based gated irradiation, depending on the respiratory-gated duty cycle settings. The proposed respiratory guidance method with personalized BFB was confirmed to be feasible in a group of volunteers. Increased effective dose rate and improved overall treatment precision were observed compared to conventional free breathing-based, respiratory-gated irradiation. Because breathing guidance curves could be established based on the respective average respiratory period and amplitude for each patient, it may be easier for patients to cooperate using this technique.

Measurement of Natural Radioactivity and Radon Exhalation Rate in Granite Samples Used in Palestinian Buildings

The activity concentrations and radon exhalation rates of natural radionuclides were measured for 40 samples of different imported fabricated granite types used in constructing Palestinian dwellings to estimate the radiation exposure in the atmosphere using high-resolution gamma-ray spectrometry. The average activity concentrations for 226Ra, 232Th and 40K radionuclides were found to vary from 18.6 to 151.2, 28.8 to 211.0 and 400.0 to 1,256.8 Bq kg−1, respectively. The overall average activity concentrations for 226Ra, 232Th and 40K were 71.0, 820 and 780.8 Bq kg−1. The average radium equivalents were found to range from 100.5 to 517.6 Bq kg−1 with a total average value of 248.2 Bq kg−1. The average absorbed dose rate was estimated at 1 m above ground level and a value of 118.2 nGy h−1 is obtained. The measured average annual effective dose rates varied from 0.24 to 1.2 mSv year−1, with a total average value of 0.58 mSv year−1. The external hazard index measured average values were found to be within 0.27–1.4 Bq kg−1 with a total average value of 0.67 Bq kg−1. The radioactivity concentration level estimated values varied from 0.7 to 3.7 Bq kg−1 with a total average value of 1.8 Bq kg−1. The radon exhalation rate values range between 3.9 and 30.6 Bqm−1 day−1. The effective radium content found to vary from 0.81 to 6.12 with an overall average value of 3.1 Bq kg−1.

Radon concentration and radon effective dose rate in dwellings of some villages in the district of Ajloun, Jordan

Indoor and soil radon concentrations were measured in the villages of Ayn-Jana, Ishtafena, Samta and Umm-Yanabe’ in the district of Ajloun, Jordan. Several factors that are strongly related to the radon concentrations are considered whether in soil such as its type or indoors such as room occupation type, floor level and building materials. In the village of Ayn-Jana, our results showed that the average radon concentration decreases gradually as the floor level increases. The highest concentration was found to be in the ground floor (35.5±5.0Bqm−3) and the lowest was in the second floor (22.9±3.2Bqm−3). Regarding the effect of ventilation rate in the same village, storage rooms revealed the highest concentration (38.8±5.4Bqm−3) while the lowest concentration was in living rooms (33.8±4.4Bqm−3). In the four villages, it was found that the highest radon concentration was in the dwellings made of clay (45.7±6.7Bqm−3) and the lowest was in dwellings made of brick (33.9±6.4Bqm−3). In general, the average indoor radon concentration in these villages was 36.3±2.3Bqm−3 and it corresponds to an average effective dose rate of 0.92±0.06mSvyr−1. These indoor radon concentrations as well as the annual effective dose are below the action level recommended by ICRP. The average radon concentration in soil of these villages was about 2.55±0.20kBqm−3, and it ranges from 2.08±0.12kBqm−3 in the village of Ayn-Jana to 3.62±0.13kBqm−3 in the village of Ishtafena.

ABSORBED DOSE RATES ABOVE SOILS AND ROCK OUTCROPS IN SELECTED AREAS OF ABEOKUTA, NIGERIA

Outdoor absorbed dose rates were measured in selected areas of Abeokuta in Nigeria; some with rock outcrops and others with soil overburden. Measurements were carried out using a Geiger Muller Survey Meter and a Global Positioning System (GPS). Result shows absorbed dose rates ranged from 1.0 x 103 to 1.3 x 103 nGy/hr among the rock outcrop areas and from 0.6 x 103 to 0.8 x 103 nGy/hr among the soil -covered areas. The average absorbed dose rate was 1180 ±3 nGy/hr for the rock outcrop areas and 689 ±3 nGy/hr for the soil -covered areas and assuming 0.4 occupancy factor, the corresponding average annual effective dose rates were calculated to be 2.89 ± 0.01 mSv/yr for the rock outcrop areas and 1.69 ± 0.01 mSv/yr for the soil –covered areas based on occupancy factor of 0.4. The mean annual effective dose rates for both the rock outcrop and soil covered areas were found to be higher than 1mSv/yr, the recommended dose limit for the public.

Gamma activity of stream sediment feldspars as ceramic raw materials and their environmental impact

In situ gamma spectrometric measurements have been performed to characterise the natural radiation that emitted from the stream sediment feldspars in Wadi El Missikat and Wadi Homret El Gergab, Eastern Desert, Egypt. The measurements of potassium (K, %), equivalent uranium (eU, ppm) and equivalent thorium (eTh, ppm) were converted into specific activities and equivalent dose rate. The average specific activities were 1402 Bq kg(-1) for K, 113 Bq kg(-1) for eU and 108 Bq kg(-1) for eTh in Wadi El Missikat, while they were 1240, 104 and 185 Bq kg(-1) in Wadi Homret El Gergab. The calculated outdoor average effective dose rates was 1.1 mSv y(-1) in wadi El Missikat and 1.3 mSv y(-1) in Wadi Homret El Gergab. The terrestrial-specific activities and effective dose rate levels of the natural radioactivity in the two areas lie within the international recommended limits for occupational feldspar quarry workers. On the other hand, these results indicated that irradiation is higher than the allowable level for members of the public. Therefore, quarrying the feldspar sediments from these locations as ceramic raw materials may yield an undesired impact on the environment, especially through the indoor applications.

RADIATION DOSES TO MEMBERS OF THE U.S. POPULATION FROM UBIQUITOUS RADIONUCLIDES IN THE BODY: PART 3, RESULTS, VARIABILITY, AND UNCERTAINTY

This paper is Part 3 of a three-part series investigating effective dose rates to residents of the United States from intakes of ubiquitous radionuclides, including radionuclides occurring naturally, radionuclides whose concentrations are technologically enhanced, and anthropogenic radionuclides. The radionuclides of interest are the (238)U series (14 nuclides), the actinium series (headed by (235)U; 11 nuclides), and the (232)Th series (11 nuclides); primordial radionuclides (87)Rb and (40)K; cosmogenic and fallout radionuclides (14)C and (3)H; and purely anthropogenic radionuclides (137)Cs-(137m)Ba, (129)I and (90)Sr-(90)Y. This series of papers explicitly excludes intakes from inhaling (222)Rn, (220)Rn, and their short-lived decay products; it also excludes intakes of radionuclides in occupational and medical settings. In this work, it is assumed that instantaneous dose rates in target organs are proportional to steady-state radionuclide concentrations in source regions. Part 1 reviewed, summarized, characterized, and grouped all published and some unpublished data for U.S. residents on ubiquitous radionuclide concentrations in tissues and organs. Part 2 described the methods used to organize the data collected in Part 1 and segregate it into the ages and genders defined by the study, including imputed missing values from the existing data, apportioned activity in bone, and imputed activity in hollow organ contents and the remainder of the body. This paper estimates equivalent dose rates to target tissues from source regions and maps target tissues to lists of tissues with International Commission on Radiation Protection (ICRP) tissue-weighting factors or to surrogate tissue regions when there is no direct match. Effective dose rates using ICRP tissue-weighting factors recommended in 1977, 1990, and 2007, are then calculated, and an upper bound of variability of the effective dose rate is estimated by calculating the average coefficients of variation (CV), assuming all variance is due to variability. Most of the data were for adult males, whose average effective dose rate is estimated to be 337 μSv y(-1) (CV = 0.65, geometric mean = 283 μSv y(-1), geometric standard deviation s(G) = 1.81) using 2007 ICRP tissue-weighting factors. This result is between the National Council on Radiation Protection and Measurements' 1987 estimate of 390 μSv y(-1) (using 1977 w(T)s) and its 2009 estimate of 285 μSv y(-1) (using 2007 w(T)s) and is higher than the United Nations Scientific Committee on the Effects of Atomic Radiation's 2000 estimate of 310 μSv y(-1) (using 1990 w(T)s). The methods and software developed for this project are sufficiently detailed and sufficiently general to be usable with autopsy data from any or all countries.

Radiometric Assessment of Natural Radioactivity Levels around Mrima Hill, Kenya

Mrima Hill, located in the South coast of Kenya is known for high natural background radiation, due to the presence of radiogenic heavy minerals such as monazites and carbonatites. The activity concentration of 238U, 232Th and 40K in soil samples from the hill have been determined by gamma ray spectrometry using NaI(Tl) detector and decomposition of measured gamma-spectra. As a measure of radiation hazard to the public, gamma radiation dose rates were also estimated. The average activity concentrations of 238U, 232Th and 40K were 207.0±11.3, 500.7±20.0 and 805.4±20.0 Bqkg-1, respectively. The mean absorbed dose rate in air is 440.7±16.8 nGyh-1 while the estimated annual average effective dose rate is 1.11±0.01 mSvy‑1. The absorbed dose rate due to gamma radiation from naturally occurring radioactive materials is above the global average value of 60 nGyh-1 (UNSCEAR, 2000). Key words: High natural background radiation, gamma ray spectrometry, NaI(Tl) detector, Mrima Hill.