Thoron levels in traditional Chinese residential dwellings

A survey on radon (²²²Rn), thoron (²²⁰Rn) and its decay products (²²⁰RnD) was conducted in Chinese traditional residential dwellings constructed with loam bricks or soil wall. The activity concentrations in 164 dwellings under investigation were 72.4±59.2 (arithmetic mean, AM) and 57.5±2.0 Bq m⁻³ (geometric mean, GM) for ²²²Rn, and 318±368 and 162±3.7 Bq m⁻³ for ²²⁰Rn, respectively. For ²²⁰RnD, 67 dwellings were studied. The AM of the ²²⁰RnD equilibrium equivalent concentration was 3.8±3.3 Bq m⁻³ with a maximum value of 15.8 Bq m⁻³. On the basis of these results, the average annual effective doses to the local residents due to radon and thoron exposure were 1.44–4.62 mSv. Thoron contributes 12.9–56.6% to the total doses. Preliminary results show that there is a relation between ²²⁰RnD in air and ²³²Th in soil. The correlation factors of outdoor and indoor were 0.88 and 0.40. The ²³²Th activity content of Chinese soil is estimated to be about two times the world average. The traditional residential dwellings with soil construction are still common in China. Further investigations on the ²²⁰Rn level in these dwelling with the aim of dose reduction are proposed.     

Activity concentrations of222Rn,220Rn,and their decay products in german dwellings,dose calculations and estimate of risk

Summary Measurements of the concentrations of²²²Rn, its short-lived decay products and of²¹²Pb -²¹²Bi were performed in 150 dwellings and in the open air in the Federal Republic of Germany. The concentration of²²²Rn was measured by electrostatic deposition of²¹⁸Po. The concentrations of the short-lived decay products were measured by air sampling and alpha-spectroscopy. It was found that inside dwellings the average potential alpha-energy concentration of the short-lived daughters is about three times higher than in the open air. The total potential alpha-energy concentration indoors amounts to 2.6 · 10^–3 Working Level (W. L.). Direct measurements of the equilibrium factor inside dwellings gave a mean value of 0.3. A strong dependence of the potential alpha energy concentration on the ventilation rate in dwellings has been observed. These ventilation effects exceed the effects caused by differences in the activity concentrations due to different building materials.The dose calculation results in an average dose to the whole lung due to the inhalation of short-lived radon daughters of about 0.05–0.2 mGy/a. An estimate of risk - based on the risk factors for uranium miners - shows an average lifetime risk of about 6 · 10^–4 for the incidence of lung cancer caused by inhalation of radon and thoron daughters in dwellings in the Federal Republic of Germany.The research programme was supported by the Bundesminister des Innern of the Federal Republic of Germany     

Study of radon/thoron exhalation rate,soil-gas radon concentration,and assessment of indoor radon/thoron concentration in Siwalik Himalayas of Jammu & Kashmir

In the present study, the soil-gas radon concentration was assessed at different depth intervals, i.e., 15 cm, 30 cm, 60 cm, and 100 cm from the 30 villages of Jammu &; Kashmir, India using RAD7, an electrostatic solid state alpha detector. The radon mass exhalation and thoron surface exhalation rate has also been measured in the selected 18 soil samples out of 30 of different grain sizes (i.e., 1 mm, 300 µm, 150 µm). The active radon and thoron concentrations were also assessed in the 20 villages. Both the exhalation rates and active radon/thoron concentration were measured using SMART Rn Duo, a portable radon monitor. The average values of soil-gas radon concentration were 210 ± 84 Bq m^?3, 1261 ± 963 Bq m^?3, 4210 ± 1994 Bq m^?3, and 671 ± 305 Bq m^?3 at the depth intervals of 15 cm, 30 cm, 60 cm, and 100 cm, respectively. The exhalation rate of radon and thoron from soil was found to decrease with the increase of grain size, as smaller soil particles make relatively more contribution to radon and thoron exhalations from the ground surface than larger soil particles. The measured Pearson's correlation coefficient was obtained as statistically significant between different quantities under two-tailed test.     

Assessments of 226Ra and 222Rn concentration in well and tap water from Sik,Malaysia, and consequent dose estimates

Abstract

The ingestion of ²²⁶Ra, inhalation, and ingestion of ²²²Rn in water is considered the primary health risk for lungs and stomach. This study presents the concentrations of ²²⁶Ra and ²²²Rn in well and tap water collected from Sik, Malaysia, using HPGe and RAD7 detectors. Maximum average concentrations of ²²⁶Ra and ²²²Rn were found 47.6?±?3.6 mBq/l and 9.3?±?1.4?Bq/l in well water, respectively, and minimum were found 17.1?±?3.6 mBq/l and 1.6?±?1.0?Bq/l in tap water, respectively. A positive correlation (R=.88) was found between ²²⁶Ra and ²²²Rn determined by HPGe and RAD7 detectors, respectively. Infants in the age group of 0–1 y appeared to be at risk with respect to the annual effective doses from ²²⁶Ra and ²²²Rn as compared to the other age groups. However, annual effective doses for all three age groups from intake of ²²⁶Ra and ²²²Rn in well and tap drinking water were found below the World Health Organization (WHO) recommended level of .1 mSv/y_.     

Doses from beta radiation in sensitive layers of human lung and dose conversion factors due to <Superscript>222</Superscript>Rn/<Superscript>220</Superscript>Rn progeny

Great deal of work has been devoted to determine doses from alpha particles emitted by ²²²Rn and ²²⁰Rn progeny. In contrast, contribution of beta particles to total dose has been neglected by most of the authors. The present work describes a study of the detriment of ²²²Rn and ²²⁰Rn progeny to the human lung due to beta particles. The dose conversion factor (DCF) was introduced to relate effective dose and exposure to radon progeny; it is defined as effective dose per unit exposure to inhaled radon or thoron progeny. Doses and DCFs were determined for beta radiation in sensitive layers of bronchi (BB) and bronchioles (bb), taking into account inhaled ²²²Rn and ²²⁰Rn progeny deposited in mucus and cilia layer. The nuclei columnar secretory and short basal cells were considered to be sensitive target layers. For dose calculation, electron-absorbed fractions (AFs) in the sensitive layers of the BB and bb regions were used. Activities in the fast and slow mucus of the BB and bb regions were obtained using the LUNGDOSE software developed earlier. Calculated DCFs due to beta radiation were 0.21 mSv/WLM for ²²²Rn and 0.06 mSv/WLM for ²²⁰Rn progeny. In addition, the influence of Jacobi room parameters on DCFs was investigated, and it was shown that DCFs vary with these parameters by up to 50%.     

Radionuclides content in grape molasses soil samples from Central Black Sea region of Turkey

The activity concentrations of radionuclides in grape molasses soil samples collected from Zile (Tokat) plain in the Central Black Sea region of Turkey were measured by using gamma spectrometer with a NaI(Tl) detector. Also, the concentrations of ²²²Rn in soil samples and air were estimated essentially taking the activity concentrations of ²²⁶Ra measured in soil samples. Grape molasses soil samples with calcium carbonate content are used for sedimentation for making molasses in this region. The average activity concentrations of ²³²Th, ²²⁶Ra, ⁴⁰K, and ¹³⁷Cs were found as 62 ± 2, 68 ± 3, 479 ± 35, and 8.0 ± 0.3 Bq kg^?1, respectively. The average concentrations of ²²²Rn in soil samples and air were estimated to be 50 kBq m^?3 and 144 Bq m^?3. From the activity concentrations, absorbed gamma dose rate in outdoor air (D), annual effective dose from external exposure (E_E), annual effective dose from inhalation of radon (E_I), and excess lifetime cancer risk (ELCR) were estimated in order to assess radiological risks. The average values of D, E_E, E_I, and ELCR were found to be 90 nGy h^?1, 110 μSv y^?1, 1360 μSv y^?1, and 4 × 10^?4, respectively.     

Radon survey in dwellings of Gansu,China: the influence of thoron and an attempt for correction

Alpha track detectors used in a previous investigation of the US National Cancer Institute and the China Ministry of Health on indoor radon ((222)Rn) in Gansu, China, proved to be influenced by (220)Rn (thoron), thus overestimating the (222)Rn level. Therefore, the detector was improved used in the previous survey. The new detectors allow discrimination between the two isotopes without any disturbance of the (222)Rn measurement. With this detector, a semi-annual study was conducted in 49 traditional dwellings of a village in Gansu. The arithmetic (AM) and geometric (GM) mean (222)Rn concentrations were 120 +/- 61 and 105 Bq m(-3) (with geometric standard deviation GSD = 1.8), respectively, while the mean (220)Rn concentrations at 2.5 cm wall distance were 430 +/- 210 Bq m(-3) (AM) and 350 Bq m(-3) (GM) with GSD = 2.3. The high thoron concentrations demonstrate the importance of the (220)Rn contribution to radiation exposure, in the investigated area. The actual level of indoor (222)Rn was about three times lower than that in the previous investigation which was affected by (220)Rn. A correction method for the radon results of the previous study is proposed, which provides (222)Rn and (220)Rn values comparable with those obtained in the study presented here.     

Spatial distribution of 222Rn concentrations and dose estimations in various waters

In this article, the levels of ²²²Rn concentrations, annual effective doses, and excess lifetime cancer risk estimations were investigated for water samples in the city of Osmaniye, located in the southern part of Turkey. The measurements were conducted using a radon gas analyzer (AlphaGUARD PQ 2000 PRO). The arithmetic average of ²²²Rn concentrations was 0.44 Bq.L^?1 with a geometric standard deviation of 0.19 and geometric average 0.41 Bq.L^?1. The results obtained were compared with the findings of other studies. All measured radon concentrations were below the values recommended by the World Health Organization and the U.S. Environmental Protection Agency. The associated radiological parameters such as annual effective doses (AED) and excess lifetime cancer risk (ELCR) from consumption of these waters were calculated. The computed average annual effective doses for ingestion and inhalation as well as excess lifetime cancer risk were estimated to be 1.13 μSv.y^?1, 1.10 μSv.y^?1, and 3.95 × 10^?6, respectively. ²²²Rn concentration, AED, and ELCR interpolated values of the region were determined and mapped using the Kriging method. The results of radon concentrations in this study provide a data baseline for future studies on subsequent evaluations of possible future environmental contamination of Osmaniye Province.     

Lead biogeochemistry in a central Ontario Forested watershed

To determine the sources and sinks of atmospherically deposited Pb at a forested watershed (Plastic Lake) in central Ontario, Canada, Pb pools and fluxes through upland, wetland and lake compartments were measured during 2002/2003 and compared with previous measurements taken between 1989 and 1991. In 2002/2003, annual bulk deposition of Pb was 0.49 mg m⁻² compared with 1.90–1.30 mg m⁻² in 1989–1991. Annual Pb concentrations in stream water draining the upland part of the catchment were very low (0.04 μg l⁻¹) and were approximately half those measured in 1989–1991 (0.11–0.08 μg l⁻¹). Leaching losses in stream water were small and mass balance estimates indicate almost complete retention (>95%) of atmospherically deposited Pb in upland soils. In contrast, annual Pb concentrations in stream water draining a wetland were between 0.38 and 0.77 μg l⁻¹, with the highest concentration occurring in 2002/2003 and mass balance calculations indicate that the wetland is a net source of Pb in all measured years. Lead concentrations in the lake outflow were low and the average Pb concentration measured in 2002/2003 (0.09 μg l⁻¹) was approximately half the value recorded in 1989–1991 (0.19 μg l⁻¹ both years). Annual mass balance estimates indicate that the lake retained between 2.47 mg m⁻² (1989/1990) and 1.42 mg m⁻² (2002/2003) and that in 2002/2003 68% of the Pb input to the lake is derived from the terrestrial catchment. These estimates are higher than sediment core records, which indicate around 18 mg m⁻² Pb was retained in sediment during the 1990s. Nevertheless, Pb concentrations decrease with sediment depth and ²⁰⁶Pb/²⁰⁷Pb concentrations increase with depth, a pattern also observed in mineral soils that reflects the substantial contribution of anthropogenic Pb to the watershed. Lead isotope data from soil and sediment indicate a recent anthropogenic Pb signal (²⁰⁶Pb/²⁰⁷Pb ∼ 1.185) in upper soils and sediments and an older anthropogenic signal (²⁰⁶Pb/²⁰⁷Pb ∼ 1.20) in deeper soil and sediment. Lead isotope data in sediment and vegetation indicate that practically all the Pb cycled in the forest at Plastic Lake is anthropogenic in origin.     

Comparison of antioxidative effects between radon and thoron inhalation in mouse organs

Radon therapy has been traditionally performed globally for oxidative stress-related diseases. Many researchers have studied the beneficial effects of radon exposure in living organisms. However, the effects of thoron, a radioisotope of radon, have not been fully examined. In this study, we aimed to compare the biological effects of radon and thoron inhalation on mouse organs with a focus on oxidative stress. Male BALB/c mice were randomly divided into 15 groups: sham inhalation, radon inhalation at a dose of 500 Bq/m³ or 2000 Bq/m³, and thoron inhalation at a dose of 500 Bq/m³ or 2000 Bq/m³ were carried out. Immediately after inhalation, mouse tissues were excised for biochemical assays. The results showed a significant increase in superoxide dismutase and total glutathione, and a significant decrease in lipid peroxide following thoron inhalation under several conditions. Additionally, similar effects were observed for different doses and inhalation times between radon and thoron. Our results suggest that thoron inhalation also exerts antioxidative effects against oxidative stress in organs. However, the inhalation conditions should be carefully analyzed because of the differences in physical characteristics between radon and thoron.

     

Air quality monitoring with regard to222Rn in buildings constructed on disused tin-mining areas

Secondary land uses have taken place on disused tin-mining areas in the form of mixed development projects consisting of housing schemes with commercial and recreational facilities. The cassiterite minerals containing tin are rich in thorium and uranium found in the xenotime and monazite minerals commonly present in the Malaysian terrains. With the upheaval of these minerals from tin-mining activities, the environment is basically exposed to the natural radioactive materials derived from the²³²Th and²³⁸U radionuclides. One of the daughter products is²²²Rn and it is known to be one of the main indoor air pollutants related to the sick-building syndrome. High concentrations of indoor²²²Rn will be hazardous to human health, which is often associated to lung cancer and other chronic diseases. The main purpose of this study is to determine the concentrations of indoor²²²Rn in residential areas constructed on former tin-mining areas with particular reference to places with high human activities such as commercial areas. Air samples were collected using the RDX-013 scintillator cell and the quantitity of²²²Rn determined by the RDA-200 radon/thoron detector. Measurements were made at different times and intervals for the purpose of looking at variations of²²²Rn levels present in the atmosphere. Results of this study showed that the concentration of indoor²²²Rn is higher in the morning (1.64 ± 0.20 pCi L) compared to the levels detected in the afternoon (1.30 ± 0.08 pCi L) for most residential areas. As expected, the concentration of²²²Rn outdoors is lower (1.08 ± 0.08 pCi L) compared to the concentration determined indoors (1.64 ± 0.20 pCi L). Recently constructed houses or buildings in commercial centers seemed to have²²²Rn concentrations relatively higher than those occupied for longer periods of time. However, the levels of²²²Rn concentrations in the study area showed that all were below the maximum permissible level of 4.0 pCi L as stipulated by the United States Environmental Protection Agency. This work also discussed the mitigation measures taken by the building management of commercial buildings to reduce the risk of²²²Rn buildup in an effort to improve public health as a result of the poor indoor air quality.     

Rapid determination of radon daughters and of artificial radionuclides in air by online gamma-ray spectrometry

For the determination of airborne radionuclide concentrations in real time, a fixed filter device was constructed which fits directly onto a germanium detector with standard nuclear electronics and a multichannel analyzer buffer connected via a data line to a personal computer for remote control and on-line spectrum evaluation. The on-line gamma-ray spectrometer was applied to the study of radon decay product concentrations in ground-level air and to the rapid detection of any contamination of the environmental air by artificial radionuclides. At Munich-Neuherberg, depending on the meteorological conditions, the measured air concentrations of²¹⁴Pb, the first gamma-ray-emitting member of the²²²Rn decay series, varied from about 1 to 50 Bq m^–3. For the artifical radionuclides⁶⁰Co,¹³¹I and¹³⁷Cs the detection limits were determined as a function of the varying natural radon daughter concentrations at sampling and counting times of 1 h or 1 day. For these radionuclides minimum detectable air activity concentrations of 0.3 or 0.001 Bq m^–3, respectively, were obtained at low radon daughter levels. At high radon daughter levels the respective detection limits were found to be higher by a factor of only about 2.Dedicated to Prof. Wolfgang Jacobi on the occasion of his 65th birthday     

Comparative study of 222Rn/220Rn progeny concentration and estimation of age-dependent dose due to inhalation of radon progeny for different body organs

In the present study, the age-dependent doses due to inhalation of short lived decay progeny of radon, i.e., ²¹⁴Po to different body organs have been calculated for the inhabitants of the Jammu district, Jammu &; Kashmir, India. The estimated age-dependent doses for different body organs due to inhalation of radon progeny through air for all age groups varied between 0.002E-06 and 0.10 n Svy^?1 which were found to be well within the recommended limit of 1000 µ Svy^?1 (ICRP). The progeny concentration of radon and thoron was calculated and compared by two different techniques. The attached and un-attached progeny concentration of radon and thoron was calculated by using a passive time integrating, deposition-based technique. The measured attached and un-attached radon and thoron progeny concentrations have been cross-checked by on-line active technique, i.e., Flow-mode Integrated Sampler. A weak positive correlation has been observed between the two devices. The median value of un-attached fraction was found to be 0.15 and 0.12 for thoron and radon progeny, respectively and found to have a log-normal distribution. A good positive correlation has been observed between radon and thoron progeny concentrations.     

A study of air particulate pollution in colombo using a nuclear-related analytical technique

Air particulate matter of two size fractions (coarse [2.5–10 Μm] and fine [less than 2.5 Μm]) were collected at an urban residential site (Colombo University ground) over a period of 12 mo during 1996 using a Gent PM10 stacked filter unit. Seventy-five sets of samples collected during this period were analyzed for 10 elements: Al, Si, K, S, Ca, Ti, Fe, Zn, Br, and Pb by energy-dispersive X-ray fluorescence, which is a multielement analysis. This is a highly sensitive technique enabling quantitative analysis of very low masses. The average concentrations of lead, sulfur, and bromine, which are generally associated with combustion products of automotive exhausts, dominate the fine fraction in this study. The minimum and maximum concentration of lead resulting in an annual average of 0.09 Μg/m³ was found to be 0.0042 and 0.441 Μg/m³ in particulate matter with less than 10 Μm equivalent aerodynamic diameter. The maximum concentration determined is well below the limits set by the World Health Organization (0.5–1.0 Μg/m³). The recommended value for Pb in Sri Lanka is 0.5 Μg/m³. Al, Si, Ca, Ti, and Fe exhibited enhanced concentrations in the coarse fraction, which probably originate from disturbed soil as a result of wind and traffic.     

Estimation of dose rate for indoor radon from building materials

The internal dose rate due to indoor radon (Rn) emissions from building materials is estimated. It is observed that the contribution from building materials to the dose rate is very small. The average indoor radon concentration in 75 different rooms is found to be 55 ± 12 Bq. m^–3. Assuming an occupancy factor of 0.8, the annual average effective dose equivalent is 1.7 mSv. It seems that soil gas is mainly responsible for the internal exposure from indoor Rn.     

Greenhouse gas fluxes from the eutrophic Temmesjoki River and its Estuary in the Liminganlahti Bay (the Baltic Sea)

We studied concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in the eutrophic Temmesjoki River and Estuary in the Liminganlahti Bay in 2003–2004 and evaluated the atmospheric fluxes of the gases based on measured concentrations, wind speeds and water current velocities. The Temmesjoki River was a source of CO₂, CH₄ and N₂O to the atmosphere, whereas the Liminganlahti Bay was a minor source of CH₄ and a minor source or a sink of CO₂ and N₂O. The results show that the fluxes of greenhouse gases in river ecosystems are highly related to the land use in its catchment areas. The most upstream river site, surrounded by forests and drained peatlands, released significant amounts of CO₂ and CH₄, with average fluxes of 5,400 mg CO₂–C m⁻² d⁻¹ and 66 mg CH₄–C m⁻² d⁻¹, and concentrations of 210 μM and 345 nM, respectively, but N₂O concentrations, at an average of 17 nM, were close to the atmospheric equilibrium concentration. The downstream river sites surrounded by agricultural soils released significant amounts of N₂O (with an average emission of 650 μg N₂O–N m⁻² d⁻¹ and concentration of 22 nM), whereas the CO₂ and CH₄ concentrations were low compared to the upstream site (55 μM and 350 nM). In boreal regions, rivers are partly ice-covered in wintertime (approximately 5 months). A large part of the gases, i.e. 58% of CO₂, 55% of CH₄ and 36% of N₂O emissions, were found to be released during wintertime from unfrozen parts of the river.     

Characteristics of thoron and thoron progeny in Canadian homes

Naturally occurring isotopes of radon in indoor air are identified as the second leading cause of lung cancer after tobacco smoking. Radon-222 (radon gas) and radon-220 (thoron gas) are the most common isotopes of radon. While the radon equilibrium factor is well established, the equilibrium factor between thoron progeny and thoron gas is still not well known. Thoron gas and progeny concentrations were determined in the lowest floors of 138 Canadian homes simultaneously. While thoron gas was only detectable in about 52% of the homes, thoron progeny concentrations were measured in every home surveyed. Thoron concentrations, thoron progeny concentrations, and the equilibrium factors varied widely and were log-normally distributed. With a 3 months simultaneous measurement of thoron and thoron progeny concentrations, the equilibrium factor was determined to be 0.024 with a geometric standard deviation of 2.7.     

Doses from radon progeny as a source of external beta and gamma radiation

Great deal of work has been devoted to determine doses from alpha particles emitted by ²²²Rn and its progeny. In contrast, contribution of beta particles and following gamma radiation to total dose has mostly been neglected so far. The present work describes a study of the detriment of ²²²Rn progeny for humans due to external exposure. Doses and dose conversion factors (DCFs) were determined for beta and gamma radiation in main organs and remainder tissue of the Oak Ridge National Laboratory phantom, taking into account ²²²Rn progeny ²¹⁴Pb and ²¹⁴Bi distributed in the middle of a standard or typical room with dimensions 4?m?×?5?m?×?2.8?m. The DCF was found to be 7.37?μSv/WLM. Skin and muscle tissue from remainder tissue receives largest dose. Beta and gamma radiation doses from external exposure were compared with alpha, beta, and gamma doses from internal exposure where the source of radioactivity was the lungs. Total doses received in all main organs and remainder tissues were obtained by summing up the doses from external and internal exposure and the corresponding DCF was found to be 20.67?μSv/WLM.     

Radiocesium in mushrooms from selected locations in the Czech Republic and the Slovak Republic

In this paper, activity concentrations of radiocesium in mushrooms from various locations in the Czech Republic and the Slovak Republic in the years 2000–2004 are presented. Summary reports of Czech regulatory bodies have judged the average activity concentrations in mushrooms to be remarkably below the maximum permissible level of contamination. However, there are certain regions where radiocesium activities have approached the maximum permissible level for contamination of basic foodstuff. For example, the highest activity concentration of ¹³⁷Cs measured by gamma-spectrometry was 2,263 Bq kg⁻¹ (on a dry mass basis), in Xerocomus badius from Staré Ransko (a locality in the Czech-Moravian Highlands, Czech Republic). The highest activity concentration of ¹³⁷Cs measured in Slovakia was 966 Bq kg⁻¹ (on a dry mass basis), for Suillus luteus from Senica. For comparison, the corresponding activity concentration in a sample taken within the 30 km zone around Chernobyl was measured to be 6,000 Bq kg⁻¹ (on a dry mass basis). Our results have also demonstrated remarkably lower activity concentrations of ¹³⁷Cs in Slovakia compared to those in the Czech Republic.     

Radioactive aerosols released from the Chernobyl Shelter into the immediate environment

The release of radioactive particles through large gaps in the containment of the destroyed Chernobyl reactor was assessed during two measurement periods. In 1996–1999, a total radionuclide flow rate of 274 Bq s⁻¹ or 8.64 × 10⁹ Bq year⁻¹ was determined. These releases were predominantly due to ¹³⁷Cs (78.5%), ⁹⁰Sr (21.1%), and ^239+240Pu (0.4%). The mean activity concentration in the aerosol measured directly at the gaps was about 240 mBq m⁻³ with an activity median aerodynamic diameter (AMAD) of 2.4 μm for ¹³⁷Cs, 120 mBq m⁻³ with an AMAD in the range 3.1–13 μm for ⁹⁰Sr, 1.8 mBq m⁻³ with an AMAD in the range 3.5–11 μm for ^239+240Pu, and 2.0 mBq m⁻³ with an AMAD of 1.5 μm for ²⁴¹Am. The resulting total inhalation dose rate calculated close to the gaps was about 100 nSv h⁻¹. In the near environment, the mean ¹³⁷Cs activity in the aerosol was 2.2 mBq m⁻³ with an AMAD of 2.2 μm, which gave rise to an inhalation dose rate of about two orders of magnitude lower than the corresponding dose rate at the gaps. Occasionally, however, dose levels were measured in the near environment that were similar to those at the gaps. In 2000–2003, lower activity concentrations were observed. The decrease was more pronounced at the gaps than in the near environment. The results indicate that effective dose due to inhalation must be considered for the dose assessment of construction workers who will be deployed at the Chernobyl site to reconstruct the old or to build the new Shelter, in the future.