RESUMO
In-situ measurements by gamma-ray spectrometry using a NaI(Tl) scintillation spectrometer are performed to discriminate primordial and artificial radionuclides contributing to ambient gamma dose rates in the living environment to quantify prolonged influence of nuclear accidents. However, low energy resolution of the spectrometer causes poor discrimination in the measurements at high-dose-rate points, which leads to overestimation of ambient gamma dose rate from the primordial radionuclides. The present study clarified that photon fluxes originating from 40K and 214Bi were affected by the presence of 134Cs, whereas those from 208Tl were independent of it. In addition, the absorbed dose rates in air were strongly correlated with the 208Tl photon fluxes. These findings indicate that 208Tl photon fluxes can be used to evaluate absorbed dose rates in air from the primordial radionuclides. When estimated from the 208Tl photon fluxes only, the absorbed dose rates in air in Namie Town and Okuma Town, locations affected by the Fukushima Dai-ichi Nuclear Power Plant accident, were 19-71 and 20-47 nGy h-1, respectively.
Assuntos
Poluentes Radioativos do Ar , Acidente Nuclear de Fukushima , Monitoramento de Radiação , Radioisótopos de Césio/análise , Monitoramento de Radiação/métodos , Poluentes Radioativos do Ar/análise , JapãoRESUMO
The Fukushima soils have been collected from Namie and Futaba areas for the radiocaesium and uranium isotope ratio studies. The 137Cs activity concentration of soil samples ranged from 6 ± 1 to 756 ± 14 kBq/kg. The uranium isotope ratios are measured using multi collector inductively coupled plasma mass spectrometry. The activity ratio (234U/238U) of the Fukushima soils is calculated from the measured 234U/238U isotope ratio. Activity ratio varied from 0.98 to 1.02 which indicates that 234U and 238U are in secular equilibrium. The 235U/238U atomic ratio of the Fukushima soils did not show any heterogeneity compared with the natural terrestrial ratio even with high level of 137Cs in soils.
Assuntos
Poluentes Radioativos do Solo , Urânio , Radioisótopos de Césio/análise , Isótopos/análise , Espectrometria de Massas/métodos , Solo , Poluentes Radioativos do Solo/análise , Urânio/análiseRESUMO
A comparison on commercially available radon (222Rn) measuring instruments (three types of continuous monitors and a passive 222Rn-thoron (220Rn) discriminative alpha track detector) was carried out at low-level concentrations in one room of a concrete building. The agreements between the continuous monitors were within 15%, while the agreements between each instrument were within 20%. It was also observed that the indoor 220Rn concentration measured by the continuous monitor was quite different from those by the passive detectors due to the mean concentration less than the limit of detection of both measuring instruments.
Assuntos
Materiais de Construção/análise , Radiometria/instrumentação , Radônio/análise , Poluição do Ar em Ambientes Fechados/análise , Japão , Monitoramento de Radiação/métodosRESUMO
Unegt subbasin in Dornogobi Province, southeastern Mongolia, contains the Dulaan Uul uranium deposit, for which development for commercial mining has been conducted as of 2015. Zuunbayan is a commune located close to the Dulaan Uul uranium deposit, and residents of Zuunbayan and their livestock can easily approach the uranium deposit area, including an aboveground dump site, which was created as a result of the mining development. The present study measured and analyzed the gamma dose rate (absorbed dose rate in air) distribution in Unegt subbasin using data collected from a car-borne measurement survey. The gamma dose rate increased from the northern (45-65 nGy/h) to the central (50-69 nGy/h, including Zuunbayan) and the southern (54-195 nGy/h, including Dulaan Uul) parts of the study area. The gamma dose rates (up to 195 nGy/h) around the dump site in Dulaan Uul were significantly higher than the background level (< 80 nGy/h) at several points. Additional in-situ measurements showed that the gamma dose rates reached up to 450 nGy/h at these locations, which was primarily attributed to the gamma radiation emitted by 238U series elements. Spatial distribution of gamma dose rates around the dump site revealed that the gamma radiation did not originate from the dump, but from the ground, at the measurement points. Analysis of collected soil samples showed that 238U and 226Ra were concentrated in deeper soil. These results indicate that the gamma dose rates higher than the background level were not associated with the aboveground mine dump; rather, they were very probably caused by presence of uranium deposits close to the ground surface.
Assuntos
Radiação de Fundo , Raios gama , Monitoramento de Radiação , Poluentes Radioativos do Solo/análise , Mineração , Mongólia , Radioisótopos de Potássio/análise , Doses de Radiação , Solo , Tório/análise , Urânio/análiseRESUMO
We observed the atmospheric resuspension of radiocaesium, derived from the Fukushima Dai-ichi Nuclear Power Plant accident, at Namie, a heavily contaminated area of Fukushima, since 2012. During the survey periods from 2012 to 2015, the activity concentrations of radiocaesium in air ranged from approximately 10-5 to 10-2 Bq per m3 and were higher in the warm season than in the cold season. Electron microscopy showed that the particles collected on filters in summer were predominantly of biological origin (bioaerosols), with which the observed radiocaesium activity concentration varied. We conducted an additional aerosol analysis based on fluorescent optical microscopic observation and high-throughput DNA sequencing technique to identify bioaerosols at Namie in 2015 summer. The concentrations of bioaerosols fluctuated the order of 106 particles per m3, and the phyla Basidiomycota and Ascomycota (true Fungi) accounted for approximately two-thirds of the bioaerosols. Moreover, the fungal spore concentration in air was positively correlated with the radiocaesium concentration at Namie in summer 2016. The bioaerosol emissions from Japanese mixed forests in the temperate zone predominately included fungal cells, which are known to accumulate radiocaesium, and should be considered an important scientific issue that must be addressed.
Assuntos
Contaminação Radioativa do Ar/análise , Radioisótopos de Cério/análise , Esporos Fúngicos/química , Contaminação Radioativa do Ar/efeitos adversos , Acidente Nuclear de Fukushima , Japão , Monitoramento de Radiação/métodos , Estações do AnoRESUMO
The present study aimed at examining changes of gamma radiation level associated with road construction in Mongolia. A car-borne survey of gamma dose rate was made for a paved, ~450-km long part of the Asian Highway 3 between Ulaanbaatar and Sainshand. The gamma dose rates ranged from 48 to 173 nGy/h. Elevation of the gamma dose rates was observed only on a 86-km long segment of the survey route which was newly constructed from 2011 to 2013. The gamma dose rates over the newer paved segment were twice as high as those over the bare dirt surface alongside it. Outdoor measurements of gamma-ray pulse height distributions also indicated an abundance of natural radionuclides, especially 232Th-series elements in road materials. These findings suggest that the gamma dose rates were elevated by introduction of road materials containing large amounts of natural radionuclides.
Assuntos
Radiação de Fundo , Materiais de Construção/análise , Poluentes Ambientais/análise , Raios gama , Monitoramento de Radiação/métodos , Medição de Risco/métodos , Monitoramento Ambiental , Humanos , Mongólia , Doses de RadiaçãoRESUMO
The spatial distribution of ambient gamma dose rates in a high-rise steel-reinforced concrete building in Fukushima, Japan, was examined relative to the gamma-ray emissions from building materials and radionuclides derived from the 2011 nuclear accident. The results revealed the minor role of accident-derived radionuclides in ambient gamma dose rates ~7 y after the accident. The ambient gamma dose rates were higher in the upper floors because of gamma-ray emissions from natural radionuclides in the floor slabs. The fractional contribution of natural radionuclides to the ambient gamma dose rates indicated compositional differences in concrete between the upper- and lower-floor slabs.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar em Ambientes Fechados/análise , Materiais de Construção/análise , Acidente Nuclear de Fukushima , Raios gama , Monitoramento de Radiação/métodos , Humanos , JapãoRESUMO
In order to evaluate internal exposure to radon and thoron, concentrations for radon, thoron, and thoron progeny were measured for 259 dwellings located in high background radiation areas (HBRAs, outdoor external dose: 3-5 mGy y-1) and low background radiation areas (control areas, outdoor external dose: 1 mGy y-1) in Karunagappally Taluk, Kerala, India. The measurements were conducted using passive-type radon-thoron detectors and thoron progeny detectors over two six-month measurement periods from June 2010 to June 2011. The results showed no major differences in radon and thoron progeny concentrations between the HBRAs and the control areas. The geometric mean of the annual effective dose due to radon and thoron was calculated as 0.10 and 0.44 mSv, respectively. The doses were small, but not negligible compared with the external dose in the two areas.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar em Ambientes Fechados/análise , Carcinógenos Ambientais/análise , Exposição Ambiental/análise , Habitação , Monitoramento de Radiação/métodos , Produtos de Decaimento de Radônio/análise , Radônio/análise , Radiação de Fundo , Humanos , ÍndiaRESUMO
The Chhatrapur placer deposit is found in a high background radiation area which has been recently identified on the southeastern coast of India. Previously, some geochemical studies of this area were carried out to assess external dose from radionuclides-bearing heavy mineral sands. In this study, radon, thoron and thoron progeny concentrations were measured in about 100 dwellings during three seasons (autumn-winter, summer, and rainy) in a 10- to 12-month period and annual doses due to inhalation of them were evaluated. The measurements were made by passive-type radon-thoron discriminative detectors and thoron progeny detectors in which solid state nuclear track detectors were deployed. The results show that radon and thoron concentrations differ by one order of magnitude depending on exposure periods, while thoron progeny concentration is nearly constant throughout the year. Since thorium-rich sand is distributed in the studied area, exposure to thoron is equal to, or exceeds, exposure to radon and is not negligible for dose evaluation. Based on the measurements, doses due to inhalation of radon and thoron are evaluated as 0.1-1.6 mSv y-1 and 0.2-3.8 mSv y-1, respectively. The total dose is 0.8-4.6 mSv y-1, which is the same order of magnitude as the worldwide value.
Assuntos
Monitoramento de Radiação , Radônio/análise , Poluentes Radioativos do Ar/análise , Radiação de Fundo , ÍndiaRESUMO
The radioactive fission product (90)Sr has a long biological half-life (Ë18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Assessing (90)Sr is therefore extremely important in case of a nuclear disaster. In this work 16 soil samples were collected from the exclusion zone (<30 km) of the earthquake-damaged Fukushima Daiichi nuclear power plant, to measure (90)Sr activity concentration using liquid scintillation counting. (137)Cs activity concentration was also measured with gamma-spectroscopy in order to investigate correlation with (90)Sr. The (90)Sr activity concentrations ranged from 3.0 ± 0.3 to 23.3 ± 1.5 Bq kg(-1) while the (137)Cs from 0.7 ± 0.1 to 110.8 ± 0.3 kBq kg(-1). The fact that radioactive contamination originated from the Fukushima nuclear accident was obvious due to the presence of (134)Cs. However, (90)Sr contamination was not confirmed in all samples although detectable amounts of (90)Sr can be expected in Japanese soils, as a background, stemming from global fallout due to the atmospheric nuclear weapon tests. Correlation analysis between (90)Sr and (137)Cs activity concentrations provides a potentially powerful tool to discriminate background (90)Sr level from its Fukushima contribution.
Assuntos
Acidente Nuclear de Fukushima , Cinza Radioativa/análise , Poluentes Radioativos do Solo/análise , Radioisótopos de Estrôncio/análise , Radioisótopos de Césio/análise , Desastres , Meio Ambiente , Geografia , Meia-Vida , Japão , Centrais Nucleares , Armas Nucleares , Monitoramento de Radiação/métodos , Solo/química , Espectrometria gamaRESUMO
This study was conducted on the Fukushima Medical University (FMU) premises (in Fukushima City, Fukushima Prefecture) about four years after the Fukushima Daiichi Nuclear Power Plant accident.ãIts objectives were (1) to create a map of the ambient gamma dose rate (air-kerma rate) distribution, (2) to evaluate the air-kerma rate originating from natural radionuclides, and (3) to investigate the effects of snow cover on changes in the air-kerma rate.ãThis man-borne survey revealed that the air-kerma rate varies widely, ranging from 0.038 µGy h(ï¼1) to 0.520 µGy h(ï¼1), and is higher on grass than on the other investigated surface types, such as soil, asphalt, and bricks.ãIn this area, the mean air-kerma rate from natural radiation was evaluated to be 0.03 ± 0.01 µGy h(ï¼1), which is close to 0.04 µGy h(ï¼1), which was measured in central Fukushima City by a local authority.Furthermore, snowfall was found to reduce the air-kerma rate by 5%-30%.ãThis reduction was attributed to attenuation of the primary radiation while passing through the snow cover, and the measured contribution of scattered radiation to the air-kerma rate reduction was small.ãThe reduction rate was found to depend on the initial snow depth but to maintain a similar value for a couple of days, after the snow had partially melted and its depth had decreased.ãFinally, analysis of the daily dose due to external exposure received on the FMU premises revealed that no further health effects due to chronic radiation exposure at this site are to be expected.
Assuntos
Acidente Nuclear de Fukushima , Monitoramento de Radiação , Humanos , Doses de Radiação , Exposição à Radiação , Neve , Fatores de Tempo , UniversidadesRESUMO
An intercomparison for continuous monitors that measure thoron ((220)Rn) concentration was carried out using a (220)Rn chamber of National Institute of Radiological Sciences (NIRS), Japan; eleven (220)Rn monitors (four types) from nine laboratories were evaluated. The (220)Rn detection principle was the same for the eleven instruments and one reference instrument, which were commercially available silicon semiconductor detectors using an electrostatic collection method. The intercomparison results showed that there was a negative deviation of more than 30% in measured (220)Rn concentrations given by the laboratories relative to the reference values, which were obtained by making a decay-correction during the travel of (220)Rn through the sampling assembly (sample tube, filter and drying unit) and using a calibration factor. In order to elucidate the reason for this and then to investigate factors that affect the (220)Rn concentration measured with the monitors. As a result, it was necessary to make the decay-correction, in particular, when using a drying unit with a large inner volume and to use the calibration factor in order to better estimate the (220)Rn concentration. It was also found to be better to determine a calibration factor inherent to an individual monitor, because the calibration factor values ranged from 0.75 to 2.32, depending on the flow rate of the monitor pump (0.37-1.02 L min(-1)). It was concluded from this study that a periodical calibration of the monitor and a check of the monitor flow rate during measurements are necessary to maintain a consistent quality level of the (220)Rn measurement.
Assuntos
Poluentes Radioativos do Ar/análise , Monitoramento de Radiação/instrumentação , Radônio/análise , Poluentes Radioativos do Ar/normas , Calibragem , Humanos , Japão , Monitoramento de Radiação/normas , Monitoramento de Radiação/estatística & dados numéricos , Radônio/normas , Valores de Referência , Eletricidade EstáticaRESUMO
The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan resulted in significant releases of fission products. While substantial data exist concerning outdoor air radioactivity following the accident, the resulting indoor radioactivity remains pure speculation without a proper method for estimating the ratio of the indoor to outdoor airborne radioactivity, termed the airborne sheltering factor (ASF). Lacking a meaningful value of the ASF, it is difficult to assess the inhalation doses to residents and evacuees even when outdoor radionuclide concentrations are available. A simple model was developed and the key parameters needed to estimate the ASF were obtained through data fitting of selected indoor and outdoor airborne radioactivity measurement data obtained following the accident at a single location. Using the new model with values of the air exchange rate, interior air volume, and the inner surface area of the dwellings, the ASF can be estimated for a variety of dwelling types. Assessment of the inhalation dose to individuals readily follows from the value of the ASF, the person's indoor occupancy factor, and the measured outdoor radioactivity concentration.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar em Ambientes Fechados/análise , Monitoramento de Radiação , Acidente Nuclear de Fukushima , Japão , Análise de RegressãoRESUMO
This paper describes preliminary experiments using a passive detector for integrating measurements of indoor thoron (²²°Rn) progeny concentrations with an aerosol chamber. A solid state nuclear detector (CR-39) covered with a thin aluminum-vaporized polyethylene plate (Mylar film) was used to detect only alpha particles emitted from ²¹²Po due to ²²°Rn progeny deposited on the detector surfaces. The initial experiment showed that Mylar film with area density of more than 5 mg cm⻲ was suitable to cut off completely alpha particles of 7.7 MeV from ²¹4Po of ²²²Rn progeny decay. In the experiment using the passive detector, it was observed that the net track density increased linearly with an increase of time-integrating ²²°Rn progeny concentration. As a result of dividing deposition rates by atom concentrations, the deposition velocity was given as 0.023 cm s⻹ for total ²²°Rn progeny. The model estimates of deposition velocities were 0.330 cm s⻹ for unattached ²²°Rn progeny and 0.0011 cm s⻹ for aerosol-attached ²²°Rn progeny using Lai-Nazaroff formulae. These deposition velocities were in the same range with the results reported in the literature. It was also found that the exposure experiments showed little influence of vertical profiles and surface orientations of the passive detector in the chamber on the detection responses, which was in good agreement with that in the model estimates. Furthermore, it was inferred that the main uncertainty of the passive detector was inhomogeneous deposition of Rn progeny onto its detection surfaces.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar em Ambientes Fechados/análise , Radônio/análise , Aerossóis , Partículas alfa , Monitoramento de Radiação/métodos , Produtos de Decaimento de Radônio/análiseRESUMO
A car-borne survey was carried out in Kerala, India to estimate external dose. Measurements were made with a 3-in × 3-in NaI(Tl) scintillation spectrometer from September 23 to 27, 2013. The routes were selected from 12 Panchayats in Karunagappally Taluk which were classified into high level, mid-level and low level high background radiation (HBR) areas. A heterogeneous distribution of air kerma rates was seen in the dose rate distribution map. The maximum air kerma rate, 2.1 µGy/h, was observed on a beach sand surface. 232Th activity concentration for the beach sand was higher than that for soil and grass surfaces, and the range of activity concentration was estimated to be 0.7-2.3 kBq/kg. The contribution of 232Th to air kerma rate was over 70% at the measurement points with values larger than 0.34 µGy/h. The maximum value of the annual effective dose in Karunagappally Taluk was observed around coastal areas, and it was estimated to be 13 mSv/y. More than 30% of all the annual effective doses obtained in this survey exceeded 1 mSv/y.
Assuntos
Automóveis , Monitoramento Ambiental/métodos , Doses de Radiação , Radioisótopos/análise , Exposição Ambiental , Humanos , Índia , Inquéritos e QuestionáriosRESUMO
This paper describes an aerosol chamber system that can be used for calibrations and performance experiments of passive (220)Rn progeny detectors. For the purpose of this study, an aerosol generation system using carnauba wax as the aerosol material was mounted into the (220)Rn chamber. We used the chamber to measure characteristics of the equilibrium factor (F) of (220)Rn and unattached fraction (f(p)) of (220)Rn progeny, which are important parameters for dose estimation. The first experiment showed that continuous and stable generation of the unattached and aerosol-attached (220)Rn progeny concentrations was obtained. We observed that the spatial distributions in the chamber of the vertical profiles of the unattached and aerosol-attached (220)Rn progeny concentrations were homogeneous, as were the particle number concentration and count median diameter. The values of F and f(p) and their characteristics observed in this study were in the same range as the values reported from indoor measurements. We found that the characteristics of F and f(p) were dependent on the aerosol conditions (particle diameter and particle number concentration).
Assuntos
Radiometria/instrumentação , Radônio/análise , Radônio/química , Aerossóis , Calibragem , Desenho de EquipamentoRESUMO
Several studies have estimated inhalation doses for the public because of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Most of them were based on measurement of radioactivity in outdoor air and included the assumption that people stayed outdoors all day. Although this assumption gives a conservative estimate, it is not realistic. The "air decontamination factor" (ratio of indoor to outdoor air radionuclide concentrations) was estimated from simultaneous sampling of radioactivity in both inside and outside air of one building. The building was a workplace and located at the National Institute of Radiological Sciences (NIRS) in Chiba Prefecture, Japan. Aerosol-associated radioactive materials in air were collected onto filters, and the filters were analyzed by γ spectrometry at NIRS. The filter sampling was started on March 15, 2011 and was continued for more than 1 year. Several radionuclides, such as (131)I, (134)Cs, and (137)Cs were found by measuring the filters with a germanium detector. The air decontamination factor was around 0.64 for particulate (131)I and 0.58 for (137)Cs. These values could give implications for the ratio of indoor to outdoor radionuclide concentrations after the FDNPP accident for a similar type of building.
Assuntos
Poluentes Radioativos do Ar/análise , Poluição do Ar/análise , Acidente Nuclear de Fukushima , Centrais Nucleares , Monitoramento de Radiação/métodos , Radioatividade , Poluição do Ar em Ambientes Fechados/análise , Japão , Radioisótopos/análise , Espectrometria gamaRESUMO
Namie Town was heavily contaminated by the Fukushima Daiichi Nuclear Power Station accident. The thyroid equivalent dose for residents who lived in Namie was estimated using results of whole body counting examinations which were carried out by the Japan Atomic Energy Agency a few months after the nuclear accident. Photon peaks of (131)I and (134)Cs were previously measured by the authors using a NaI(Tl) scintillation spectrometer and that information was used to estimate the (131)I/(134)Cs activity ratio of total intake in the present study. The maximum values of (131)I/(134)Cs activity ratio corresponding to thyroid uptake factors of 0.3, 0.1 and 0.03 were evaluated to be 0.9, 2.6 and 8.7, respectively. The maximum value of the (131)I/(134)Cs activity ratio was used to obtain the most conservative thyroid equivalent dose estimation. The maximum internal exposure of the thyroid to (131)I on the basis of (134)Cs accumulated in the body measured by the whole body counter was estimated to be 18mSv. This value was much smaller than 50mSv that the International Atomic Energy Agency recommends as the dose at which exposed persons should take stable iodine tablets.
Assuntos
Poluentes Radioativos do Ar/análise , Isótopos de Césio/análise , Exposição Ambiental , Acidente Nuclear de Fukushima , Radioisótopos do Iodo/análise , Glândula Tireoide/química , Adolescente , Adulto , Idoso , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Japão , Masculino , Pessoa de Meia-Idade , Contagem Corporal Total , Adulto JovemRESUMO
Radionuclide concentrations in environmental samples such as surface soils, plants and water were evaluated by high purity germanium detector measurements. The contribution rate of short half-life radionuclides such as (132)I to the exposure dose to residents was discussed from the measured values. The highest values of the (131)I/(137)Cs activity ratio ranged from 49 to 70 in the environmental samples collected at Iwaki City which is located to the south of the F1-NPS. On the other hand, the (132)I/(131)I activity ratio in the same environmental samples had the lowest values, ranging from 0.01 to 0.02. By assuming that the (132)I/(131)I activity ratio in the atmosphere was equal to the ratio in the environmental samples, the percent contribution to the thyroid equivalent dose by (132)I was estimated to be less than 2%. Moreover, the contribution to the thyroid exposure by (132)I might be negligible if (132)I contamination was restricted to Iwaki City.
Assuntos
Monitoramento Ambiental , Acidente Nuclear de Fukushima , Monitoramento de Radiação , Poluentes Radioativos do Ar/análise , Poluentes Radioativos do Ar/química , Meia-Vida , Humanos , Radioisótopos do Iodo/análise , Radioisótopos do Iodo/química , Japão , Radioisótopos/análise , Radioisótopos/química , Poluentes Radioativos do Solo , Poluentes Radioativos da ÁguaRESUMO
This study examined correlations between radon, thoron and thoron progeny concentrations based on surveys conducted in several different countries. For this purpose, passive detectors developed or modified by the National Institute of Radiological Sciences (NIRS) were used. Radon and thoron concentrations were measured using passive discriminative radon-thoron detectors. Thoron progeny measurements were conducted using the NIRS-modified detector, originally developed by Zhuo and Iida. Weak correlations were found between radon and thoron as well as between thoron and thoron progeny. The statistical evaluation showed that attention should be paid to the thoron equilibrium factor for calculation of thoron progeny concentrations based on thoron measurements. In addition, this evaluation indicated that radon, thoron and thoron progeny were independent parameters, so it would be difficult to estimate the concentration of one from those of the others.