Environmental Dose Research Articles

Intercomparison exercise on external gamma dose rate under field conditions at the laboratory of natural radiation (Saelices el Chico, Spain)

The last nuclear accident in Fukushima nuclear power plant has increased the necessity for measuring radiation in the environment. Therefore, radiation monitors providing results traceable throughout the country become essential and it is very important to test them under the same environmental conditions. The first intercomparison of natural radioactivity under field conditions was held in Saelices el Chico (Salamanca, Spain) in May 2011, including an exercise on environmental dose rate. This article presents the results achieved by 19 instruments belonging to 12 institutions from 7 different countries. The tested detectors are proportional counters, ionisation chambers, Geiger-Müller and scintillators measuring dose rate in three stations with reference values from 110 to 1800 nGy h(-1). All the results were given in terms of air kerma (nGy h(-1)) and the measurements show agreement within 25 % in all the sites. Evaluation criteria based on accuracy and statistical uncertainty were also carried out and 25 % of participants passed the test in all sites.

Differences in Rates of Decrease of Environmental Radiation Dose Rates by Ground Surface Property in Fukushima City After the Fukushima Daiichi Nuclear Power Plant Accident

After the Great East Japan Earthquake on 11 March 2011, the environmental radiation dose in Fukushima City increased. On 11 April, 1 mo after the earthquake, the environmental radiation dose rate at various surfaces in the same area differed greatly by surface property. Environmental radiation measurements continue in order to determine the estimated time to 50% reduction in environmental radiation dose rates by surface property in order to make suggestions for decontamination in Fukushima. The measurements were carried out from 11 April to 11 November 2011. Forty-eight (48) measurement points were selected, including four kinds of ground surface properties: grass (13), soil (5), artificial turf (7), and asphalt (23). Environmental radiation dose rate was measured at heights of 100 cm above the ground surface. Time to 50% reduction of environmental radiation dose rates was estimated for each ground surface property. Radiation dose rates on 11 November had decreased significantly compared with those on 11 April for all surface properties. Artificial turf showed the longest time to 50% reduction (544.32 d, standard error: 96.86), and soil showed the shortest (213.20 d, standard error: 35.88). The authors found the environmental radiation dose rate on artificial materials to have a longer 50% reduction time than that on natural materials. These results contribute to determining an order of priority for decontamination after nuclear disasters.

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.

Soil genesis, optical dating, and geoarchaeological evaluation of two upland Alfisol pedons within the Tertiary Gulf Coastal Plain

Much of the Gulf Coastal Plain is mantled by sandy A and E soil horizons overlying finer-grained Bt horizons. Researchers have applied optical stimulated luminescence (OSL) dating to a variety of depositional settings, such as hillslopes and terraces, in an attempt to understand depositional versus pedogenic origins of the sandy horizons, and archaeological burial processes. These investigations have documented a range of integrity conditions from pristine to highly bioturbated. However, little work has been conducted in upland summits. Thus, we integrated field morphological descriptions, constituent mass balance reconstruction, and optical dating to reconstruct the timing and pedogenic pathways of two summit Alfisols on the Tertiary Gulf Coastal Plain in Texas. Investigations reveal that the sandy A and E horizons and the Bt horizons in each pedon are genetically related, with textural contrasts resulting from pedogenic processes. Optical dating revealed highly complex age structures strongly influenced by bioturbation, weathering, and the presence of coarse clay plus total silt particle-sizes. Pedogenic mixing is extensive in the A and E horizons, which effect apparent OSL ages <10,000years due to admixture of recently and partially bleached grains to the matrix. Decreased mixing occurs within the argillic horizon of each pedon, and ages increase systematically with depth. In all horizons pedogenic weathering and mixing have altered the 40K, U and Th content and environmental dose rates, with concomitant changes in OSL ages. Apparent maximum age calculations provide insight into the most probable oldest equivalent dose group and suggest that the investigated soils began to weather no later than 90–112ka, and 40–62ka, respectively, which greatly precedes human entry of into North America. High overdispersion of equivalent dose values in the sandy horizons reflects on-going pedoturbation, which varies between pedons and may result in differential archaeological preservation potential.

Determining the cooling age using luminescence-thermochronology

Luminescence technique has been shown to have great potential in low-temperature (<100°C) themochronology. This study investigates the kinetic process of luminescence in a cooling system. We present a new formula that can be used for determining the cooling age based on luminescence-thermochronology. The cooling rate can be obtained directly from a plot of luminescence age versus the present temperature. We show that the application and capacity of luminescence-thermochronology are significantly controlled by the saturation of luminescence and environmental dose rate.

Evaluation of environmental contamination and estimated radiation doses for the return to residents' homes in Kawauchi Village, Fukushima prefecture.

To evaluate the environmental contamination and radiation exposure dose rates due to artificial radionuclides in Kawauchi Village, Fukushima Prefecture, the restricted area within a 30-km radius from the Fukushima Dai-ichi Nuclear Power Plant (FNPP), the concentrations of artificial radionuclides in soil samples, tree needles, and mushrooms were analyzed by gamma spectrometry. Nine months have passed since samples were collected on December 19 and 20, 2011, 9 months after the FNPP accident, and the prevalent dose-forming artificial radionuclides from all samples were 134Cs and 137Cs. The estimated external effective doses from soil samples were 0.42–7.2 µSv/h (3.7–63.0 mSv/y) within the 20-km radius from FNPP and 0.0011–0.38 µSv/h (0.010–3.3 mSv/y) within the 20–30 km radius from FNPP. The present study revealed that current levels are sufficiently decreasing in Kawauchi Village, especially in areas within the 20- to 30-km radius from FNPP. Thus, residents may return their homes with long-term follow-up of the environmental monitoring and countermeasures such as decontamination and restrictions of the intake of foods for reducing unnecessary exposure. The case of Kawauchi Village will be the first model for the return to residents’ homes after the FNPP accident.

Optically stimulated luminescence (OSL) as a chronometer for surface exposure dating

We pioneer a technique of surface‐exposure dating based upon the characteristic form of an optically stimulated luminescence (OSL) bleaching profile beneath a rock surface; this evolves as a function of depth and time. As a field illustration of this new method, the maximum age of a premier example of Barrier Canyon Style (BCS) rock art in Canyonlands National Park, Utah, USA, is constrained. The natural OSL signal from quartz grains is measured from the surface to a depth of &gt;10 mm in three different rock samples of the Jurassic Navajo Sandstone. Two samples are from talus with unknown daylight exposure histories; one of these samples was exposed at the time of sampling and one was buried and no longer light exposed. A third sample is known to have been first exposed 80 years ago and was still exposed at the time of sampling. First, the OSL‐depth profile of the known‐age sample is modeled to estimate material‐dependent and environmental parameters. These parameters are then used to fit the model to the corresponding data for the samples of unknown exposure history. From these fits we calculate that the buried sample was light exposed for ∼700 years before burial and that the unburied sample has been exposed for ∼120 years. The shielded surface of the buried talus sample is decorated with rock art; this rock fell from the adjacent Great Gallery panel. Related research using conventional OSL dating suggests that this rockfall event occurred ∼900 years ago, and so we deduce that the rock art must have been created between ∼1600 and 900 years ago. Our results are the first credible estimates of exposure ages based on luminescence bleaching profiles. The strength of this novel OSL method is its ability to establish both ongoing and prior exposure times, at decadal to millennial timescales or perhaps longer (depending on the environmental dose rate) even for material subsequently buried. This has considerable potential in many archeological, geological and geo‐hazard applications.

Distribution of terrestrial gamma radiation dose rate in the eastern coastal area of Odisha, India

Terrestrial gamma radiation is one of the important radiation exposures on the earth's surface that results from the three primordial radionuclides (226)Ra, (232)Th and (40)K. The elemental concentration of these elements in the earth's crust could result in the anomalous variation of the terrestrial gamma radiation in the environment. The geology of the local area plays an important role in distribution of these radioactive elements. Environmental terrestrial gamma radiation dose rates were measured around the eastern coastal area of Odisha with the objective of establishing baseline data on the background radiation level. The values of the terrestrial gamma radiation dose rate vary significantly at different locations in the study area. The values of the terrestrial gamma dose rate ranged from 77 to 1651 nGy h(-1), with an average of 230 nGy h(-1). During the measurement of the terrestrial gamma dose rate, sand and soil samples were also collected for the assessment of natural radionuclides. The activities of (226)Ra, (232)Th and (40)K from these samples were measured using a gamma-ray spectrometry with a NaI(Tl) detector. Activity concentrations of (226)Ra, (232)Th and (40)K ranged from 15.6 to 69 Bq kg(-1) with an average of 46.7 Bq kg(-1), from 28.9 to 973 Bq kg(-1) with an average of 250 Bq kg(-1) and from 139 to 952 Bq kg(-1) with an average of 429, respectively. The detailed significance of these studies has been discussed from the radiation protection point of view.

Environmental contamination and external radiation dose rates from radionuclides released from the Fukushima nuclear power plant

To evaluate the environmental contamination and contributory external exposure after the accident at the Fukushima Nuclear Power Plant (FNPP), the concentrations of artificial radionuclides in soil samples from each area were analysed by gamma spectrometry. Six artificial radionuclides ((131)I, (134)Cs, (137)Cs, (129m)Te, (95)Nb and (136)Cs) were detected in soil samples around FNPP. Calculated external effective doses from artificial radionuclide contamination in soil samples around FNPP were 1.9-2.9 μSv h(-1) (8.7-17.8 mSv y(-1)) in Fukushima city on 22 March 2011. After several months, these calculated external effective doses were 0.25-0.88 μSv h(-1) (2.2-7.6 mSv y(-1)) in Fukushima city on 29 June 2011. The present study revealed that the detected artificial radionuclides around FNPP mainly shifted to long-lived radionuclides such as radioactive caesium ((134)Cs and (137)Cs) even though current levels are decreasing gradually due to the decay of short-lived radionuclides such as (131)I, (129m)Te, (95)Nb and (136)Cs. Thus, radiation exposure potency still exists even though the national efforts are ongoing for reducing the annual exposure dose closer to 1 mSv, the public dose limit. Long-term environmental monitoring around FNPP contributes to radiation safety, with a reduction in unnecessary exposure to the residents.

Comparative optical and radiocarbon dating of laminated Holocene sediments in two maar lakes: Lake Keilambete and Lake Gnotuk, south-western Victoria, Australia

Sediment core chronologies of optical dates on single-grains/very small aliquots of sand-sized quartz are compared with Accelerator Mass Spectrometry (AMS) radiocarbon (14C) chronologies from ostracod carbonate, mixed carbonates, sedimentary organic matter and charcoal in order to establish the age of laminated Holocene sediments in maar crater lakes Keilambete and Gnotuk, Victoria, Australia. Samples for optical and AMS 14C dating were taken from the same Mackereth cores, allowing a direct comparison of the two techniques from two laminated sedimentary sequences. Additional AMS 14C samples were taken from water in Lake Keilambete and from groundwater discharging into Lake Keilambete from the crater wall, with equivalent reservoir ages of 150 ± 30 and 1940 ± 30 years respectively.AMS 14C dating of modern ostracod carbonate in Lake Keilambete demonstrates a reservoir age of 670 ± 175 years. Optical dating of ‘single-grain/very small aliquots’ of sand-sized-quartz indicate the presence of a radiocarbon reservoir in Lake Keilambete that is consistent with that measured on modern ostracods, and also demonstrate that there is no 14C reservoir in Lake Gnotuk during the Holocene. The chronology presented here supports the premise that previously published bulk conventional 14C dates from Lake Keilambete were affected by old carbon, meaning that past chronologies require revision.Limitations on the use of optical dating of single-grain/very small aliquots include the relative paucity of sand-sized quartz, which decreases the precision of the sample equivalent dose (De), and is further confounded by low environmental dose rates and resultant large uncertainties on the final age assessment. Nevertheless, evidence for partial bleaching confirms that single-grain quartz dating is the most appropriate luminescence technique, and may prove a useful alternative in situations where 14C dating is unsuitable or an alternative chronometer is required.

Direct OSL dating of Iron Age pottery from South Africa – Preliminary dosimetry investigations

A pilot study used eleven excavated sites in the Limpopo Province of South Africa to test the application of OSL dating for Iron Age ceramic shards. The culture-history sequences of Iron Age is well established by pottery style and the sites had already been radiocarbon dated. Because the excavations were part of various research projects, rather than a specific OSL study, the sites have been destroyed and hence, local environmental radioactivity was unknown. To reconstruct the environmental dose rate, we used data from three sources: (1), a worldwide survey, (2), radionuclides in the pottery and (3) recent geological surveys. The geological surveys yielded the most dates that are reasonably close to the known chronology, reproducing the correct chronological order in most cases. Some dates, however, are 200 years too recent and some standard deviations too high. To evaluate further the potential of OSL dating in Iron Age research, dosimetry data need to be collected in situ.

Radioactivity Levels and Health Risks due to Radionuclides in the Soil of Yalova, Northwestern Turkey

Naturally occurring radionuclide of terrestrial origin (also called primordial radionuclide) are present in various degrees in all media in the environment, including the human body itself. Their concentrations in environment decrease continually by decaying. The main objective of this study is to evaluate the radioactivity levels and health risks due to terrestrial radionuclide in soil of Yalova, northwestern Turkey. For this purpose, activity concentrations of radionuclide in soil and the environmental outdoor gamma dose rates (terrestrial and cosmic) have been investigated in the city of Yalova. In addition, maps for the radionuclide activity concentrations of soil and the outdoor gamma dose rates distributions have been plotted for the region. The average activities of radionuclide, 238 U, 232 Th, 226 Ra, 40 K, and 137 Cs in the soil were determined as 17.95 (8.5-37.3) Bq/kg, 26.87 (3.8-43.9) Bq/kg, 22.36 (8.3-41) Bq/kg, 419.32 (197.1-950.0) Bq/kg, 2.53 (0.5-13.4) Bq/kg, respectively, in the region. The average outdoor gamma dose rates due to terrestrial and cosmic radiations were found to be 49 nGy/h and 35 nGy/h with the total of 84 nGy/h outdoor gamma exposure rate in the region. Annual effective dose due to environmental outdoor gamma radiation exposures was determined as 103 nSv with the excess lifetime cancer risk of 0.042 x 10 -2 in the region. The results of the study were discussed with the studies done in the close cities and the worldwide averages.

Radiation protection in an animal research unit with pet: Occupational doses and dose rates produced by animals

Abstract This study focuses on the occupational doses of technologists working at an Animal Research Unit using PET radiotracers and on the environmental dose rates produced by the animals (mice, rats and monkeys). In particular, whole body and extremity monitoring is reported and related with the workload. The study shows that doses not only depend on the amount of activity injected but also on the type of animals and radiotracers managed. The extremities, with a great variability of the doses received, are the limiting organs as far as regulatory dose limits for workers are concerned. Mean H∗(10) rates in contact and at 20 cm from the animals, when they are handled by the technologist, range from around 1 mSv/h to 20 μSv/h, respectively.

Measurement of environmental gamma-ray dose rate around the Nuclear Fuel Cycle Engineering Laboratories, JAEA

The Nuclear Fuel Cycle Engineering Laboratories (NCL), JAEA operates the Tokai Reprocessing Plant (TRP), plutonium fuel fabrication facilities and the supplemental facilities. In the terrestrial environment, environmental gamma-ray dose rate was measured continuously using an energy-thermo-compensation-type NaI(Tl) scintillation detector. The data of environmental dose rate measured in 5 monitoring stations and 8 monitoring posts were collected and analyzed to monitor on real-time. This paper summarizes the monitoring data of environmental dose rate around the NCL during the past 10 year (fiscal 1998-2007). The averages of the environmental dose rate for all monitoring stations and posts were in the range of 32-45 nGy h -1 . The long-term variation in the environmental dose rate was not found. The cases of the short-term increases occurred by the operations of the facilities in the NCL were concluded to the discharges of 85 Kr from the TRP, transportation of MOX fuels or radioactive solid wastes, X-ray generator to calibrate the radiation monitoring instruments. The other cases to affect the change of the environmental dose rate were the scavenging of the airborne natural radionuclides, a patient cured by the radiation therapy and the shield effect by cars.

Radiation protection for an intra-operative X-ray device

Therapeutic partial breast irradiation can be delivered intra-operatively using the Intrabeam 50 kVp compact X-ray device. Spherical applicators are added to the source to give an isotropic radiation dose. The low energy of this unit leads to rapid attenuation with distance, but dose rates are much greater than for diagnostic procedures. To investigate the shielding requirements for this unit, attenuation measurements were carried out with manufacturer-provided tungsten-rubber sheets, lead, plasterboard and bricks. A prospective environmental dose rate survey was also conducted in the designated theatre. As a result of isotropic geometry, the scattered dose around shielding can be 1% of primary and thus often dominates measured dose rates compared with transmission. The absorbed dose rate of the unshielded source at 1 m was 11.6 mGy h(-1) but this was reduced by 95% with the shielding sheets. Measured values for the common shielding materials were similar to reference data for the attenuation of a 50 kVp diagnostic X-ray beam. Two lead screens were constructed to shield operators remaining in the theatre and an air vent into a service corridor. A lead apron would also provide suitable attenuation, although a screen allows greater flexibility for treatment operators. With these measures, staff doses were reduced to negligible quantities. Survey measurements taken during patient treatments confirmed no additional measures were required, but the theatre should be a controlled area and access restricted. Results from this study and reference data can be used for planning other facilities.

Comparative study of the dose rate influence in the radiochromic polymeric film dosimeter response

Most of film dosimetry is based on optical signal measurements since the spectrophotometric technique is cheap and widespread. Radiation induced chemical reactions take place in the material creating and/or enhancing absorption bands in the visible and/or ultraviolet regions of the spectrum. The response of most films used in routine dosimetry is usually influenced by the environmental conditions (temperature, humidity, ligth), dose rate and post irradiation storage. Several film dosimeters are commercially available for the absorbed dose measurements, in this work the effects of dose rate changes in optical density (OD) of film dosimeters (polymethylmetacrylate – PMMA and polycarbonate – PC) were investigated and compared. Polycarbonates has been investigated as a new dosimetric material for industrial radiation processing aiming low cost, easy handle, fast and accurate response. PMMA dosimeters has been used routinely in dosimetry. The dose rate (kGy h−1) may influence the dosimeter response and appropriate corrections are necessary. The dosimeters were irradiated with 60Co gamma-radiation at dose rate in the range 0.26 – 2.6 kGy h−1 and with electrons from accelerator with maximum energy of 1.5 MeV and dose rate between 4.19 and 33.59 kGy s−1 to absorbed doses of 5 and 15 kGy, respectively. The irradiated dosimeters were measured using Shimadzu UV-2101PC spectrophotometer. It can be observed that the films shows moderate dose-rate dependence (about 10%) in the analised range.

Determination of the variation of environmental radiation due to the ground deposition of atmospheric 222Rn decay products during rainfall: utilization of the correlation between the variations observed at neighboring monitoring posts

The increase of environmental radiation dose rate during rainfall at environmental monitoring posts (MPs) was calculated by using the correlation relationship with the dose rate at the neighboring MP. The calculated dose rate agreed with the observed one within less than 20% of the maximum increase height of the observed one for each rainfall. Furthermore, when the dose rate increased due to Krypton-85 (85Kr) discharged from the Tokai Reprocessing Plant (TRP) at the environmental monitoring station (MS) downwind of the stack during rainfall, the dose rate due to the 85Kr was tried to discriminate. The discriminated dose rate agreed with that calculated by the atmospheric dispersion calculation code system, SIERRA-II, using stack monitor data and local meteorological observation data.

Long-Term Continuous In-Situ Measurement of Gamma Rays Using Ge Semiconductor Detector

We developed a long-term continuous measurement method for in-situ gamma-ray measurement using a Ge semiconductor detector (in-situ Ge measurement), and performed continuous measurement for 36 months by the method. A measurement system was successfully stably operated for a long period, and it was confirmed that artificial radioactive nuclides were able to be detected at high sensitivity. A counting rate of each of 214Pb and 214Bi was increased about twice in correspondence to slight increase in environmental radiation dose rate of about 10% as a measurement value of a monitoring post using a NaI (Tl) detector. The problem of discriminating between natural radiation and radiation from man-made source was solved by this system.

Effect of deposit alterations on the dating of herbivorous teeth from Arago cave by the ESR–U-series method

Geochemical alteration processes in archaeological sites may affect the environmental dose rate during the burial history and cause inaccuracy in age determination by palaeodosimetric dating methods, such as luminescence or ESR. In Arago Cave (Tautavel, France), the original composition of the sandy aeolian sediments of palaeoanthropological level G, where the Homo heidelbergensis Arago XXI skull was found, has been modified by both carbonation and phosphatization processes. Eight fossil teeth were collected from different geochemically affected parts of level G and analyzed by the ESR–U-series method. All the teeth are presumably contemporaneous. The results show that the samples from the phosphated area agree within error with those from the carbonated area. Surprisingly, the samples from the non-altered area show ages 100–150 ka younger. This difference is mainly due to the remarkable changes in the gamma dose rate over time. The measured in situ dose rate accounts for more than 50% of the total dose rate for all the samples. We observed that the samples' equivalent dose ( D E) were generally 20% lower in the non-altered area than in the carbonated and phosphated ones. These results show the crucial effect of the geochemical processes affecting the age calculation by ESR–U-series method in comparison with independent chronological data.

Variation of radon concentrations in soil and groundwater and its correlation with radon exhalation rate from soil in Budhakedar, Garhwal Himalaya

Radon was measured in soil-gas and groundwater in the Budhakedar area of Tehri Garhwal, India in summer and winter to obtain the seasonal variation and its correlation with radon exhalation rate. The environmental surface gamma dose rate was also measured in the same area. The radon exhalation rate in the soil sample collected from different geological unit of Budhakedar area was measured using plastic track detector (LR-115 type II) technique. The variation in the radon concentration in soil-gas was found to vary from 1098 to 31,776 Bq.m−3 with an average of 7456 Bq.m−3 in summer season and 3501 to 42883 Bq.m−3 with an average of 17148 Bq.m−3 in winter season. In groundwater, it was found to vary from 8 to 3047 Bq.l−1 with an average value 510 Bq.l−1 in summer and 26 to 2311 Bq.l−1 with an average value 433 Bq.L−1 in winter. Surface gamma dose rate in the study area varied from 32.4 to 83.6 μR.h−1 with an overall mean of 58.7 μ-R.h−1 in summer and 34.6 to 79.3 μR.h−1 with an average value 58.2 μR.h−1 in winter. Radon exhalation rate from collected soil samples was found to vary from 0.1 × 10−5 to 5.7 × 10−5 Bq.kg−1.h−1 with an average of 1.5 × 10−5 Bq.kg−1.h−1 in summer season and 1.7 × 10−5 to 9.6 × 10−5 Bq.kg−1.h−1 with an average of 5.5 × 10−5 Bq.kg−1.h−1. A weak negative correlation was observed between radon exhalation rate from soil and radon concentration in the soil. Radon exhalation rate from the soil was also not found to be correlated with the gamma dose rate, while it shows a positive correlation with radon concentration in water in summer season. Inter-correlations among various parameters are discussed in detail.