Activity Concentrations In Air Research Articles

Soil and air radon/thoron exhalation rates and radon activity concentrations in the vicinity of Lake Monoun, West region of Cameroon

ABSTRACTOne crucial element to determine the radon amount in the environment is the rate at which radon is exhaled from the subsurface. To assess the radon and thoron potential exhalation in the vicinity of Monoun Lake in the West Region of Cameroon, 28 soil samples were collected around the lake. Radon activity concentration in soil gas and air and the related risk to radon inhalation were evaluated. Radon and thoron exhalation rates, mass exhalation rates, and radon soil gas activity concentrations were derived from a mathematical model as a function of radium content and soil parameters. Radium activity concentrations were estimated using a gamma-ray spectrometry technique with a High Purity Germanium detector (HPGe). The average radon exhalation rate, thoron exhalation rate, radon mass exhalation rate, and thoron mass exhalation rate were found to be 22.7 mBq.m−2.s−1, 5348 mBq.m−2.s−1, 0.018 mBq.kg−1.s−1, and 321 mBq.kg−1.s−1, respectively. The registered radon and thoron exhalation rates were above the world average values of 16 Bq.m−2.s−1 and 1000 Bq.m−2.s−1 published by UNSCEAR, respectively. The calculated thoron exhalation in the study area was about 75.3 times higher than that of radon, which suggests probably more exposure to thoron gas than the radon in the area, despite its shorter half-life. A good positive correlation was found between radon and thoron exhalation rates. The obtained average values of radon activity concentrations in air and annual effective dose were above the world average values of 10 Bq.m−3 and 0.095 mSv published by UNSCEAR, but still below the threshold values of 148 Bq.m−3 and 1.4 mSv set as action levels by USEPA, respectively.

Plutonium isotopes in the ground air layer in southern Poland (2010–2016): Source terms, seasonal variability and correlations with meteorological conditions

In this study, the results of the analysis of Pu-238 and Pu-239 + 240 activity concentrations on aerosol filters collected from 2010 to 2016 in Krakow (Southern Poland) are presented and discussed. For the first time, the temporal variation of Pu-239 + 240 activity concentration in surface air in Poland was studied using Fourier analysis. The analysis clearly showed that the Pu-239 + 240 content in the near-ground air layer is subject to seasonal variations and demonstrates annual periodicity. Pu analyses were performed using alpha spectrometry. The measured values ranged from 1.93∙10−10 Bq/m3 to 1.31∙10−8 Bq/m3 with an average of 2.07∙10−9 Bq/m3 for Pu-239 + 240 and from 9.07∙10−11 Bq/m3 to 1.27∙10−9 Bq/m3 with the average 1.52∙10−10 Bq/m3 for Pu-238. The analysis of the potential sources of plutonium isotopes in the air aerosols samples indicated that only two samples are uniquely characterized by the ratio corresponding to spent nuclear fuel: February 2012 (0.59 ± 0.18) and February 2015 (0.68 ± 0.19). The remaining samples showed mixed origins, with global radioactive fallout appearing to contribute more than spent nuclear fuel. To study the relationship between Pu-239 + 240 and meteorological conditions, Pearson's correlation and circulation pattern analyses were performed. The analyses showed that the Pu-239 + 240 activity concentration depends on air temperature (R = 0.51), the sum of ice and snowfall (R = −0.45), relative humidity (R = −0.54) and mean total cloud cover (R = −0.56). High concentrations of Pu-239 + 240 were positively correlated with air advection from the southern and eastern sectors, whereas low concentrations were observed during dynamic weather conditions with intense circulation from the western sector. In case of Pu-238 no significant correlation was observed.

Evolution of traceable radon emanation sources from MBq to few Bq

In the framework of the EMPIR project traceRadon, stable atmospheres with low-level radon activity concentrations have to be produced for calibrating radon detectors designed to measure outdoor air activity concentrations. The traceable calibration of these detectors at very low activity concentrations is of special interest to the radiation protection, climate observation, and atmospheric research communities.Radiation protection networks (such as the EUropean Radiological Data Exchange Platform (EURDEP)) and atmospheric monitoring networks (such as the Integrated Carbon Observation System (ICOS)) need reliable and accurate radon activity concentration measurements for a variety of reasons, including: the identification of Radon Priority Areas (RPA); improving the sensitivity and reliability of radiological emergency early warning systems (Melintescu et al., 2018); for more reliable application of the Radon Tracer Method (RTM) to estimate greenhouse gas (GHG) emissions; for improved global “baseline” monitoring of changing GHG concentrations and quantification of regional pollution transport (Chambers et al., 2016), (Chambers et al., 2018); and for evaluating mixing and transport parameterisations in regional or global chemical transport models (CTMs) (Zhang et al., 2021), (Chambers et al., 2019).To achieve this goal, low activity sources of radium with a variety of characteristics were produced using different methods. Sources ranging from MBq 226Ra down to several Bq 226Ra were developed and characterised during the evolution of production methods, and uncertainties below 2 % (k=1) were achieved through dedicated detection techniques, even for the lowest activity sources. The uncertainty of the lowest activity sources was improved using a new online measurement technique for which the source and detector were combined in the same device. This Integrated Radon Source Detector device, henceforth an IRSD, reaches a counting efficiency approaching 50 % through detection under quasi 2π sr solid-angle. At the time of this study the IRSD was already produced with 226Ra activities between 2 Bq and 440 Bq.To compare the working performance of the developed sources (i.e., to establish a reference atmosphere), study the stability of the sources, and to establish traceability to national standards, an intercomparison exercise was carried out at the PTB facility. Here we present the various source production techniques, the determination of their radium activity, and determination of their radon emanation (including assigned uncertainties). This includes details of the implementation of the intercomparison set-up, and a discussion of the results of the source characterisations.

Trends, events and potential sources of Xe-detections in the German radioxenon network

The measurement of radioxenons (133Xe, 131mXe, 133mXe, 135Xe) in the atmosphere is a keystone for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). At the German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS) activity concentrations of radioactive noble gases at several sites in Germany have been measured for more than 5 decades, initially to monitor nuclear facilities and since the mid-1990s also to support the development of measurement and monitoring systems and procedures for verification of the CTBT. Average 133Xe activity concentration in air measured daily at station RN33 of the International Monitoring System (IMS) of the CTBTO on Mt Schauinsland has decreased since 2008. Due to the decreasing radioxenon background in the atmosphere, laboratory measurements with less sensitive proportional counters developed in-house are increasingly replaced by an isotope specific β-γ laboratory system for radioxenon analyses. Six years of radioxenon activity concentrations measured with the β-γ laboratory system in weekly samples from monitoring sites in Germany are presented. Activity concentrations of 133Xe in southern Germany are now typically below 1 mBq m−3 and have decreased by an order of magnitude in the past 25 years. Magnitude and variability of 133Xe activity concentrations are generally larger in northern and western Germany compared to the south, most likely due to the prevailing wind directions in the region. Selected, but typical, periods of elevated radioxenon levels at the stations are investigated and the value of stack emission data is demonstrated.

Factors influencing radon transport in the soils of Moscow.

This article delves into the factors that may influence radon flux, such as soil properties and weather conditions, on the example of two experimental locations with different soil compositions, composed primarily of clay and sand, respectively. The experimental location with sandy soil was previously observed to have anomalously high radon flux levels. Radon monitoring was performed routinely, approximately at the same time of day and in parallel on both of these locations to exclude the influence of diurnal variations. The results show that radon transport in these locations differs in mechanism: Location with clay soil has diffusive radon transport, with an average radon flux density of 37.4 ± 24.9mBqm-2s-1 and a range of 0.3-167.8mBqm-2s-1, while the location with sandy soil has convective radon transport with an average radon flux density of 93.6 ± 51.2mBqm-2s-1 and a range of 9.8-302.2mBqm-2s-1. This corresponds to about 8.3% of RFD measurements on site with clay soils exceeding the national reference level of 80mBqm-2s-1 and 45.6% exceeding them on the site with sandy soils. Average radon flux density values were then compared to meteorological variables using Pearson correlation analysis with Student's t-test. It was observed that radon flux density correlates the most with ambient air temperature both for diffusive and convective radon transport mechanisms, while a weaker inverse correlation is observed with atmospheric precipitation and wind speed for the diffusive mode of radon transport, but not for the convective. Radon activity concentration in soil air correlates with the radon flux density and air temperature in the case of convective radon transport, but does not correlate in the case of diffusive transport.

Derivation of the maximum permissible activity concentrations in exhaust air

Abstract Within the scope of the amendment of the Radiation Protection Ordinance, it became necessary to lay down new limit values, as a result of both the modifications made in the stipulations of the EU directives, and improvements in the level of scientific and technological advancement. This led, at the same time, to the necessity of recalculating the permitted levels for activity concentrations in exhaust air from applications involving isotopes (mostly from medical installations). The following article provides an overview of the approach applied in the recalculation of the permitted activity concentration levels in exhaust air for around 800 radionuclides, along with a comparison of the limit values which have been applied up until the present.

Recent Progress in Radon Metrology at IFIN-HH, Romania

The practical implementation of the European Council Directive no. 2013/59/EURATOM in Romania requires reliable indoor measurements of the radon (222Rn) activity concentration in air. In Romania, several Testing Laboratories were designated for radon activity and/or radon activity concentration in air measurements by the Romanian National Commission for Nuclear Activities Control (CNCAN). The calibration of the instruments used for indoor radon activity concentration measurements is very important. IFIN-HH, through its Ionizing Radiation Metrology Laboratory (LMRI), performed advanced research in the field of radon metrology, using radon standard sources prepared by LMRI, its radon chamber facility and a new reference radon monitor. The most recent results are described in this article. The radon chamber facility from IFIN-HH was technically improved, and new equipment and methods were set up and tested in order to provide new calibration services for customers. Additionally, calibration of the radon monitors was performed, as well as of the systems with solid-state nuclear track detectors, used for radon in air activity concentration measurements. IFIN-HH/LMRI obtained the CNCAN designation as Calibration Laboratory for installations measuring the radon activity concentration in air.

Five Years (2014–2018) of Beta Activity Concentration and the Impact of Synoptic and Local Meteorological Conditions in Bilbao (Northern Spain)

The aim of this paper is to statistically characterize gross beta activity concentrations in ground-level air in Bilbao (northern Spain) by analysing five years (2014–2018) worth of weekly measurements in aerosols collected in filters to analyse the impact of local meteorological parameters on concentrations. In addition, synoptic meteorological scenarios associated with anomalous beta surface activity concentrations were identified. Over this five-year period, beta activity concentrations ranged from 35.45 µBq/m3 to 1778 µBq/m3 with a mean of 520.12 ± 281.77 µBq/m3. A positive correlation was found with the alpha concentrations (0.67), with an average of 0.138 for the alpha/beta ratio, and a low correlation was found with 7Be (0.16). Statistical analysis identified a seasonal component in the time series, increasing, on average, beta activity concentrations from winter to autumn. The highest beta activity concentrations were measured under the arrival of southerly land winds with low wind speeds, while the wind analysis (surface winds and air masses) of two different seasonal periods (autumn 2015 and winter 2017) have highlighted how small variations in synoptic and local winds highly influence beta activity concentrations. These results are relevant to understand the meteorological factors affecting beta activity concentrations in this area and hence to define meteorological scenarios that are in favour to high/anomalous surface activity concentrations that are harmful to the environmental and public health.

Estimation of radon excess lung cancer near some dumpsites in, Lagos, Nigeria

Generally, in Nigeria dumpsites are open and elevate the pollution by increasing the total environment contamination level. This affects not only the site of dumpsites but also the surrounding buildings and area. In the present work, indoor radon activity concentration is tested inside some buildings in the vicinity of dumpsites in Lagos, Nigeria. A passive technique with CR-39 detectors is used. Different buildings around different eight dumpsites were chosen. Radon concentration had ranged from 16.00 ± 3 to 931.00 ± 186 Bqm−3 in the dumpsites. With Mean concentrations range from 120 ± 24 at OKE-ODO to 334 ± 67, at Solus-4 respectively. The present results explain that 63% of the radon activity concentration in indoor air around the selected dumpsites at Lagos city in Nigeria is below the allowed limit from ICRP 200 Bq m-3 while 37% is more than this limit. Based on the measured radon concentration, the annual effective dose and cancer risk are evaluated. The range of ELC is from 242 to 14086 with mean value 3114 ± 1111.

Dosimetry of radon progeny deposited on skin in air and thermal water.

It is held that the skin dose from radon progeny is not negligibly small and that introducing cancer is a possible consequence under normal circumstances as there are a number of uncertainties in terms of related parameters such as activity concentrations in air and water, target cells in skin, skin covering materials, and deposition velocities. An interesting proposal has emerged in that skin exposure to natural radon-rich thermal water as part of balneotherapy can produce an immune response to induce beneficial health effects. The goal of this study was to obtain generic dose coefficients with a focus on the radon progeny deposited on the skin in air or water in relation to risk or treatment assessments. We thus first estimated the skin deposition velocities of radon progeny in air and thermal water based on data from the latest human studies. Skin dosimetry was then performed under different assumptions regarding alpha-emitting source position and target cell (i.e. basal cells or Langerhans cells). Furthermore, the impact of the radon progeny deposition on effective doses from all exposure pathways relating to ‘radon exposure’ was assessed using various possible scenarios. It was found that in both exposure media, effective doses from radon progeny inhalation are one to four orders of magnitude higher than those from the other pathways. In addition, absorbed doses on the skin can be the highest among all pathways when the radon activity concentrations in water are two or more orders of magnitude higher than those in air.

A multi-year study of natural radionuclides Beryllium-7 (Be-7) activity concentrations in surface air in Tanah Rata, Cameron Highlands, Pahang

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty that bans any nuclear explosions, either for military or civil purposes. The treaty is supported by an international network of monitoring stations, which inter-alia include radionuclide monitoring stations. Malaysia is a Member State to the CTBT and hosts a radionuclide monitoring station (Site code: RN42) in Tanah Rata, Cameron Highlands, Pahang. The continuous daily measurement at RN42 has created an invaluable resource for understanding variations in natural background radioactivity, including natural radionuclide, Beryllium-7 (Be-7). This study aims at assessing seasonal variations of Be-7 in surface air in Tanah Rata, Cameron Highlands, Pahang and determining its correlation with local meteorological parameters using statistical analysis. The results have been found that Be-7 activity concentration at the RN42 showed a seasonal variation and strong inverse correlation with precipitation data. The findings from this study could serve as basis for further studies on local and regional radiological impact assessment as well as for exploring the potential application of Be-7 as atmospheric tracer for civil and scientific purposes.

Study on Method for Simultaneous Determination of Ambient Dose Equivalent Rates and Activity Concentration in Air for Environmental Radiation Monitoring

Study on Method for Simultaneous Determination of Ambient Dose Equivalent Rates and Activity Concentration in Air for Environmental Radiation Monitoring

Оцінка внеску пилової бурі 16 квітня 2020 р. в радіоактивне забруднення атмосфери в період лісових пожеж у зоні відчуження Чорнобильської АЕС

On April 16, 2020, a strong dust storm was observed in the northern regions of Ukraine, which coincided with the period of intense wildland fires in the Chornobyl exclusion zone. The activity of 137Cs in aerosol particles released into the atmosphere as a result of resuspension from burned areas in the meadow biocenoses in the exclusion zone is evaluated in the article. Resuspension of radioactively contaminated particles from burned areas formed after fires in meadow biocenoses of the exclusion zone can be a powerful source of air contamination in the zone itself, as well as increase of the radionuclides transport outside it. The total 137Cs activity that entered the atmosphere during the dust storm was estimated to be about 162 GBq, i. e. up to 20% of the total activity emitted in the air during the entire period of forest fires on April 3–20, 2020. The 137Cs emission from burned areas during the dust storm on April 16 and 17 amounted to 0.24% of the total stock of 137Cs activity in this territory. According to the results of modeling, the relative contribution of wildland fires and resuspension due to the dust storm on April 16 and 17 significantly depends on the distance to the emission sources. It was found that the resuspension of radioactive particles from burned areas during the dust storm determined 80–95% of the 137Cs activity concentration in the surface air near Chornobyl nuclear power plant and in Chornobyl city and the rest was due to the continuing forest fires in neighboring territories. The maximum 3-hour averaged value of the 137Cs activity concentration in the air due to resuspension from the burned areas was obtained for the location of the monitoring post VRP-750 of SSE “Ecocenter” to be about 28 mBq/m3 for the period 9–12 hours on April 16. In Kyiv, the 3-hour averaged 137Cs activity concentration due to the dust storm in the Exclusion Zone was calculated as 44 μBq/m3 in the period from 9 to 12 hours on April 17, 2020. This value was only about 4% of the total 137Cs activity in the air in this period.

New S-chamber Mid-Term electrets: Experimental characterization and uncertainty evaluation

Electret ion chambers are widely used passive detectors, employed for measurements of radon activity concentration in air. These devices are made of a Teflon electret coupled to an interchangeable ion chamber. A new type of electret produced by Rad Elec Inc., named Mid-Term, is used together with the S-type (200cm3) chamber. It is designed to be operated in an intermediate range with respect to the standard Short-Term and Long-Term electrets. This work describes the complete characterization of such device, performed according to the ISO guidelines. The characterization was carried out in the secondary standard calibration laboratory of Politecnico di Milano Italy, and with a traceable radon chamber. The coefficients and equations presented can be used by operators to assess both the radon activity concentration and the related uncertainty, with the only requirement of the knowledge of the background gamma air kerma rate of the specific measurement site and its related uncertainty.

Дисперсность, морфология и элементный состав аэрозольных частиц на производстве смешанного нитридного уран‑плутониевого топлива

Purpose: Study of physical and chemical properties of radioactive aerosols formed on the fabrication of mixed nitride uranium-plutonium (MNUP) fuel.
 Material and methods: The following impactors were utilized for activity particle-size distribution analysis: AIP-2, PHRT, IRAM-2-4I (SRC FMBC), Andersen cascade impactor (Copley Scientific, UK), SKC Sioutas (SKC inc., USA). Scanning electron microscope (SEM) Tescan LYRA-3 equipped the X-ray microanalyzer X-max 80 (Oxford Instruments) was used for study of morphological characteristics of aerosol particles. Secondary ion-mass spectrometer Cameca IMS-1280 and track analysis were used for search of particles containing the uranium and plutonium radionuclides. 
 Results: Values of AMAD (Σa) vary from 12 µm till 30 µm, for 239Pu – from 14 till 27 µm. Lowest AMAD values (0.4–2.5 µm for 239Pu) were found in the repair area near the glove box of synthesis and sintering. The samples contain a much larger number of uranium-containing particles, which is likely due to a larger mass fraction of uranium oxide compared with plutonium dioxide in the initial mixture of reagents. Elemental composition of aerosol particles includes U (63–86 %), Pu (5–10 %) and О (9–47 %), Fe – in some samples till 32 %. Other elements like Nа, S, N, Р are contained in rather lowest amounts not exceeding 1–8 %. Only one nitrogen-containing particle was found (3 % of N).
 Conclusion: Coarse fraction of radioactive aerosols makes a major contribution in activity concentration in air of the operator zone which is driven by such operations as pressing and crushing. Aerosol particles are presented as individual particles or dense aggregates by size of 0,2– 2 µm and also as conglomerates by size 0,5–4 µm consisting of oxides (or carbides) of silicon, iron, calcium, etc. containing inclusions (200–400 nm) or individual particles (20–200 nm) of mixed U-Pu oxide or uranium oxide on the surface of conglomerate as well aslocated in the near-surface layers inside.

Development and calibration of a method for direct measurement of 220Rn (thoron) activity concentration

The interest in the measurement of thoron (220Rn) activity concentration in air has recently increased, with the attention for the development of standards useful for the calibration of measuring instruments. Due to its short half-life (55.8 s), consolidated techniques for the realization and the use of controlled atmospheres of radon (222Rn) are not effective in the case of thoron. New adequate methodology are required. A method for the measurement of the thoron reference activity based on the direct detection of the alpha particles produced by the decay of 220Rn, from natural samples containing 232Th, is here proposed. The possibility of observing an acceptable spectrum is entrusted to the realization of measurement chambers small enough to reduce as much as possible the energy loss of the alpha particles before they reach the Silicon detector. Such a chamber was realized and used with a known thoron atmosphere in a controlled environment. The experimental results are compared with those obtained from the simulation with the Monte Carlo method: (i) the alpha spectra coming directly from thoron atoms exhibit similar shape with a linear trend plus an exponential trend on the left side of the 220Rn peak, depending from the distance between source and detector; (ii) the corresponding 220Rn detection efficiency values are compatible considering the uncertainties. An investigation was conducted to study the shape of the 220Rn spectra vs the different volume of chambers, through Monte Carlo simulations. The results show: (i) the linear part of the spectra shape goes to reduce with the increasing of the height of the chamber; (ii) the 220Rn detection efficiency decreases with the increasing of the height of the chamber.

RECONSTRUCTION OF THE RADIOACTIVE CONTAMINATION OF THE TERRITORY OF UKRAINE BY IODINE-131 DURING INITIAL PERIOD OF THE CHORNOBYL ACCIDENT USING THE RESULTS FROM NUMERICAL MODEL WRF

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

Analysis of 7Be and 210Pb concentration and 7Be/210Pb activity ratio in ground level air in Palermo (Italy)

ABSTRACTA series of measurements of particulate samples collected on paper filters in Palermo (Italy) during 1995–2005 has been performed to detect Pb air activity concentration and, along with previous similar data on Be, to evaluate their activity ratio. Average values for the daily activity concentrations of Be and Pb are found to be 4.7 and 0.6 mBq m, respectively, 9.8 being the average activity ratio. Data confirm a seasonal behavior for both radionuclides. A correlation between Be and Pb air activity concentrations seems to exist, despite their different origins. The time behaviors of both Be and Pb air concentrations and Be/Pb activity ratio have been compared with some meteorological parameter time series. The analysis of the data shows a weak correlation with rainfall, while no correlation can be established with other parameters. Monthly and weekly average values have been reconstructed taking into account missing data, in order to carry out homogeneous comparisons with available data from other geographical areas. Data series correlations and the frequency analysis show the importance of atmospheric transport processes and the influence of meteorological and climatic parameters (in particular rainfall) in determining the concentrations in air of both radionuclides.

Calibration of CR-39 for different heights of radon dosimeters and application of radon concentration in Mahajran River sediment in Basra Governorate, Iraq

Radon and its progenies are the main cause of lung cancer when they are trapped inside the lungs. Therefore, the radon activity concentration in air, water and soil samples should be measured, monitored and analysed. In this paper, river sediment samples collected from 30 different locations of Mahajran River, Basra, Iraq, were studied by using solid-state nuclear track detector type CR39. The track detector used for this purpose must be calibrated for concentrations of radon, Thoron and their daughters likely to be found in samples. The chamber used in the present calibration work had a volume of 125 L and contained a standard radon source (226Ra) and radon distribution fan. Results illustrated the dependence of the CR-39 calibration factor on the dosimeter height. The calibration factor used in this application was 0.34±0.0 Tr/cm2·day / Bq·m−3 for a height of 10 cm.

Radiocesium concentration in indoor air during residential house cleaning in Fukushima Dai-ichi nuclear power plant evacuation areas

After the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, outdoor decontamination was conducted by the Japanese Government, whereas indoor contamination was the responsibility of individual residents. However, no data exist regarding 137Cs exposure during indoor cleaning. Therefore, indoor 137Cs radioactivity concentrations in indoor air were determined during cleaning in 60 houses within the evacuation area near the FDNPP, Fukushima Prefecture, Japan. Radiocesium activity concentrations per cubic meter of indoor air during dusting (mean ± SD (median)) was 6.8 ± 7.9 (4.7) and 1.6 ± 2.7 (0.78) Bq/m3 for all aerodynamic diameter of aerosol particle and PM2.5, respectively. Radiocesium activity concentrations in indoor air decreased with decreasing the aerodynamic diameter of aerosol particles (mean: 0.099, 0.22, 0.41, 0.92, 2.2, and 2.9 Bq/m3 for the aerodynamic diameter of <0.25, 0.25–0.5, 0.5–1.0, 1.0–2.5, 2.5–6.6, and >6.6 μm, respectively) and was inversely proportional to the square of the distance from the FDNPP. Indoor 137Cs radioactivity concentrations were significantly higher during dusting than during vacuuming with either a cyclone handy cleaner or a normal vacuum cleaner. The mean deposited activities in tracheobronchial and alveolar regions was estimated to be 1.9 and 2.8 Bq, respectively, during a 2-h dusting period in the studied houses. For values below the detection limit, half of the detection limit was used for calculating the means and SDs.