222Rn Concentration In Air Research Articles

Seasonal variation of background counting rates in liquid scintillation counting

A liquid scintillation background sample was measured daily in a custom-built TDCR counter for more than 17 months. The double and triple coincidence counting rates exhibit an annual sinusoidal fluctuation with a maximum in winter and a minimum in summer. Possible correlations with air temperature, air humidity, radon concentration and secondary cosmic radiation were investigated. The observation of a correlation with the ambient dose equivalent rate H˙*(10)SCR originating from the charged component of secondary cosmic radiation and an anti-correlation with the effective atmospheric temperature Teff suggest that the seasonal fluctuations in the background counting rate may be primarily driven by temporal variations in the muon flux at ground level. Additionally, a correlation was found with the indoor 222Rn concentration in air.

Variations and influence factors of 210Pb-specific radioactivity in modern calcite depositions in a subtropical cave, South China

Although 210Pb dating has been successfully used in speleothems, the understanding of the factors impacting 210Pb variations in modern calcite depositions in karst caves is poor due to the lack of in situ monitoring. Here, we studied the 210Pb variations in drip water and modern calcite depositions at five sampling sites in Maomaotou Big Cave in Guilin, south China, through more than three years of in situ monitoring. In this work, the air 222Rn concentrations, weights and 210Pb-specific radioactivity of modern calcite depositions showed significant temporal and spatial variations. The modern calcite deposition weights and 222Rn concentrations in the air of Maomaotou Big Cave ranged from 0.02 to 6.04 g and 62.9–628 Bq.m−3 (higher values in summer-autumn and lower values in winter–spring), respectively, while the 210Pb-specific radioactivities in calcite depositions varied from 7.33 to 658.52 Bq•kg−1, with lower values reported in summer–autumn and higher values in winter–spring. The opposite seasonal trends observed for the 222Rn concentrations and 210Pb-specific radioactivity indicated that the air 222Rn concentration was not the dominant factor influencing the 210Pb-specific radioactivity in the modern calcite depositions. This study concluded that 210Pb-specific radioactivity in modern calcite depositions is mainly carried by drip water; further, the remarkable negative correlation between deposition weight and 210Pb-specific radioactivity in modern calcite depositions suggests that the Constant Initial Concentration model (CIC) is fit for recent speleothem dating in a closed system. Such important information may provide a scientific basis for cave deposition dating using 210Pb.

Limitations in the assessment of radon dose: the role of activity measurements in the human body

Radon-222 is classified in the Group I of the human carcinogens. The in situ decay of inhaled 222Rn and its short-lived decay products (T1/2 <30 min) is the main source of radiation burden to the general population of natural origin. The corresponding effective dose is routinely calculated as the product of the 222Rn concentration in air, a predetermined dosimetric constant and a factor that depends on the space type (e.g. residential or public building, cave, mine, etc). However, in practice, there are large spatial and temporal variations in the activity ratio of each progeny to 222Rn in air, the characteristics of the progeny carrying particles and the metabolism of each progeny depending on air quality, as well as differences in the anatomic and physiological characteristics between individuals, that vary substantially even with time. Therefore, the currently employed dosimetric approach may introduce large uncertainties. In the hypothetical case of acute deposition and full retention in the human body of equal activities of all 222Rn progeny, about 93% of the effective dose is due to the decaying 214Po. The 214Po activity can be assessed by measurement of its γ-emitting precursor, 214Bi, which is in full equilibrium with 214Po in the human body. The 214Bi activity can be measured using a high-sensitivity whole-body counter with high counting uniformity, such as the one in use at the Ioannina University Medical Physics Department. Its detection efficiency and its dependence on body shape and size were assessed by Monte Carlo simulations. Measurements carried out in healthy adult volunteers residing at a short distance from the counter, indicated a mean total body 214Bi activity (TBBi) of ~100 Bq during the cold season of the year and lower during the hot one. Higher mean TBBi levels were found in male than in female adults. Therefore, TBBi measurements may allow for accurate radon-related risk assessment on individual base.

Effect of spring water on the radon concentration in the air at Masutomi spa in Yamanashi Prefecture, Japan

The concentrations of 222Rn existing in air have been studied by using a convenient and highly sensitive Pico-rad detector system at Masutomi spa in Yamanashi Prefecture, Japan. The measurements in air were carried out indoors and outdoors during the winter of 2000 and the summers of 1999 and 2005. The concentrations of 222Rn in spring water in this region were measured by the liquid scintillation method. The concentrations of natural radionuclides contained in soils surrounding spa areas were also examined by means of the γ-ray energy spectrometry technique using a Ge diode detector to investigate the correlation between the radionuclides contents and 222Rn concentrations in air at each point of interest. The atmospheric 222Rn concentrations in these areas were high, ranging from 5 Bq/m3 to 2676 Bq/m3. The radon concentration at each hotel was high in the order of the bath room, the dressing room, the lobby, and the outdoor area near the hotel, with averages and standard deviations of the concentration of 441 ± 79 Bq/m3, 351 ± 283 Bq/m3, 121 ± 5 Bq/m3, and 23 ± 1 Bq/m3, respectively. The source of 222Rn in the air in the bath room is more likely to be the spring water than the soil. The spring water plays carries the radon to the atmosphere. Our measurements indicated that the 222Rn concentration in the air was affected by the 222Rn concentration in spring water rather than that in soil.

Contribution of 222Rn-bearing water to indoor radon and indoor air quality assessment in hot spring hotels of Guangdong, China

This study investigates the contribution of radon ( 222Rn)-bearing water to indoor 222Rn in thermal baths. The 222Rn concentrations in air were monitored in the bathroom and the bedroom. Particulate matter (PM, both PM 10 and PM 2.5) and carbon dioxide (CO 2) were also monitored with portable analyzers. The bathrooms were supplied with hot spring water containing 66–260 kBq m −3 of 222Rn. The results show that the spray of hot spring water from the bath spouts is the dominant mechanism by which 222Rn is released into the air of the bathroom, and then it diffuses into the bedroom. Average 222Rn level was 110–410% higher in the bedrooms and 510–1200% higher in the bathrooms compared to the corresponding average levels when there was no use of hot spring water. The indoor 222Rn levels were influenced by the 222Rn concentrations in the hot spring water and the bathing times. The average 222Rn transfer coefficients from water to air were 6.2 × 10 −4–4.1 × 10 −3. The 24-h average levels of CO 2 and PM 10 in the hotel rooms were 89% and 22% higher than the present Indoor Air Quality (IAQ) standard of China. The main particle pollutant in the hotel rooms was PM 2.5. Radon and PM 10 levels in some hotel rooms were at much higher concentrations than guideline levels, and thus the potential health risks to tourists and especially to the hotel workers should be of great concern, and measures should be taken to lower inhalation exposure to these air pollutants.

On quantitative determination of radon concentration by γ-ray spectrometry of aerosol filters

The problem of determining the 222Rn concentration in air from γ-ray spectra of radon progeny is solved using the aerosol filters method. The systematic error of the method due to incomplete collection of radon progeny is determined. It is shown that, when comparing the filter activity to the analytical calculation, the use of a 20-cm-diameter 20-cm-tall NaI(Tl) crystal and a 4−π geometry makes it possible to measure radon concentration with an accuracy of 20-30%.

222Rn and 220Rn concentrations in soil gas of Karkonosze–Izera Block (Sudetes, Poland)

Soil gas 222Rn and 220Rn concentrations were measured at 18 locations in the Karkonosze–Izera Block area in southwestern Poland. Measurements were carried out in surface air and at sampling depths of 10, 40 and 80 cm. Surface air 222Rn concentrations ranged from 4 to 2160 Bq m −3 and 220Rn ranged from 4 to 228 Bq m −3. The concentrations for 10 and 40 cm varied from 142 Bq m −3 to 801 kBq m −3 and 102 Bq m −3 to 64 kBq m −3 for 222Rn and 220Rn, respectively. At 80 cm 222Rn concentrations ranged from 94 Bq m −3 to >1 MBq m −3. The 220Rn concentrations at 80 cm varied from 45 Bq m −3 to 48 kBq m −3. The concentration versus depth profiles for 222Rn differed for soils developed on fault zones, uranium deposits or both. Atmospheric air temperature and soil gas 222Rn and 220Rn were negatively correlated. At sampling sites with steep slopes, 220Rn concentrations decreased with depth.

Estimation of the radiological risk related to the presence of radon 222 in a hydrotherapycentre in Tunisia

The 222Rn concentration in air was measured in a thermal water spa used as a hydrotherapy centre inTunisia. The associated health risk for employees and patients due to the inhalation of222Rn and its progeny was estimated. A protection scheme for theemployees of the spas has been designed. Results show that the222Rn concentration variesin the range 33–589 Bq m−3. The 222Rn concentrations measured in the present study show lower values incomparison to those reported for thermal spas in other countries. The222Rn concentration in different rooms of the spa depends mainly on the ventilation rate. A modelbased on a dosimetric approach was adopted to estimate the radon risk considering the222Rn concentration, the time spent in the spa, and the radioactive equilibrium factorF. Theannual effective dose was found to vary between 0.2 and 1.7 mSv for workers while the range for patientswas from 2.8 × 10−4 to 1.1 × 10−4 mSv. These values are within the ICRP recommended values.

Studies on internal exposure doses received by the cuban population due to the intake of radionuclides from the environmental sources

Studies for the determination of radionuclide concentrations in foodstuffs, water and air were carried out in Cuba for the estimation of annual committed effective doses to members of the public as a result of environmental radionuclides via ingestion and inhalation. As a result of these studies, it was possible to determine the concentrations of 226Ra, 210Pb, 210Po, 232Th, 90Sr and 137Cs in different food groups that constitute the diet of the Cuban population, as well as the 222Rn concentrations in air. Based on these results and using previously obtained results for doses due to the 40K body content, the annual committed effective doses due to the intake of studied radionuclides were estimated. An average value of 120+/-4 microSv y-1 was obtained for doses due to ingestion of food and water and the obtained value for 222Rn inhalation was 240+/-1 microSv y-1. Using the representative value obtained previously for 40K (150+/-40 microSv y-1) and assuming a dose of 50+/-50 microSv y-1 for the probable contribution of 220Rn by inhalation, a representative value of 560+/-20 microSv was estimated for the average annual committed effective doses due to ingestion and inhalation of radionuclides for the Cuban population. Obtained values are consistent with the expected results, taking into account the characteristics of Cuban exposure scenarios, with low-activity concentration levels in environmental objects and high air exchange rates in dwellings: These results are in the same order of magnitude as results obtained by other authors and the reference values established by the USNCEAR.

Contribution of 222Rn-bearing water to the occupational exposure in thermal baths

The present study investigates the short- and long-term effects of radon (222Rn) released from water on the progeny exposure in a thermal spa. For the purposes of this work, the Polichnitos spa was used as a case study. The bathroom was supplied with water containing 110–210 kBq m−3 of 222Rn. The 222Rn concentration in air and the short-lived 222Rn progenies in attached and unattached form were monitored into the bathroom and the surrounding premises. The equilibrium factor (F-factor) and the unattached fraction were estimated. The results of this study show that water flow during bath filling is by far the dominant mechanism by which 222Rn is released in the air of the bathroom. The progeny exposure was correlated linearly with the 222Rn concentration in the entering water. The annual effective dose received by a worker was found to be below the lower limit value of 3 mSv recommended by ICRP 65. The dose limit was exceeded only for water containing more than 300 kBq m−3.

Laboratory scale studies on mitigation of high 222Rn concentrations in air and water

In view of the occasional occurrence of high 222Rn concentrations in air and water under certain circumstances, and in view of the potential health hazards of increased levels of 222Rn in respirable air and in potable water, mitigation of such high 222Rn concentration has become of primary concern. To facilitate the study of the efficiency of the various 222Rn mitigating factors simple laboratory systems were used. Altered alkali granite was used as radon source to enrich air and a piece of pitchblende was used as radon source to enrich water samples. Both enriched media will then be subjected to the mitigation treatments. Charcoal canister technique along with gamma spectrometry were used to measure 222Rn concentrations in air before and after the different mitigating treatments. These were: use of ventilation, radon barriers such as geo-membranes and aluminum sheet, and sealant such as epoxy and vinyl tape. Regarding high levels of 222Rn in air ventilation was the most efficient mitigating factor. Standard liquid scintillation counting was used to measure 222Rn concentrations in water before and after the different mitigation treatments. These were: use of aeration, activated charcoal and heating. Regarding high levels of 222Rn in water, aeration using bubblers and large volume of air was most effective in removing radon from water in a short time. However all the mitigating factors proved effective, in different degrees in decreasing 222Rn concentrations in the respective media. The result from these studies are in general agreement with reports in the literature. It can be concluded then that the different 222Rn mitigating factors can be tested and compared effectively under controlled conditions using simple laboratory scale systems.

Variations of the ambient dose equivalent rate in the ground level air

The ambient dose equivalent rate is caused by ionizing radiation of radionuclides in the atmosphere and on the ground surface as well as by cosmic radiation. Seasonal and diurnal variations of the ambient dose equivalent rate (ADER) in the ground level air are influenced by the concentration of 222Rn daughters. The 222Rn concentration in the ground level atmosphere, in turn, depends on the rate of the 222Rn exhalation from soil and turbulent air mixing. Its diurnal and seasonal variations depend on meteorological conditions. The aim of this study is to estimate the influence of variations of the rate of the 222Rn exhalation from soil and its concentrations in the ground level air on variations of ADER in the ground level air, as well as the dependence of these parameters on meteorological conditions.The 222Rn diffusion coefficient and its exhalation rate in undisturbed loamy soil have been determined. The 222Rn concentration in the soil air and its concentration in the ground level air correlate inversely (correlation coefficient is r = –0.62). The main factors determining the 222Rn exhalation from soil are: the soil temperature (r = 0.64), the difference in temperature of soil and air (r = 0.57), and the precipitation amount (r = 0.50). The intensity of gamma radiation in the ground level air is mostly related to the 222Rn concentration in the air (r = 0.62), while the effect of the exhalation rate from soil is relatively low (r = 0.36).It has been shown that ADER due to 222Rn progeny causes only 7–16% of the total ADER and influences its variation. The comparison of variations of ADER due to 222Rn progeny and the total ADER during several years shows that these parameters correlate positively.

Seasonal variations of 222Rn concentrations in the air of a tunnel located in Nagano city

The seasonal variation of 222Rn concentrations in the air of tunnels constructed during World War II at Nagano City has been investigated. The determination of 222Rn concentrations in tunnel air was performed using a solid-state nuclear track detector technique. The monthly radon concentrations changed smoothly, decreasing towards winter and increasing towards summer, and it was found that the concentrations strongly correlate with the temperature difference between the inside and the outside of the tunnel. In the innermost areas of the tunnel, the maximum concentration was observed in July, its value being about 6500 Bq m −3. The concentrations of radon in the tunnel air decrease exponentially towards the openings of the tunnel, which indicates that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air. These observations lead to the conclusion that the seasonal variation of the radon concentration in the tunnel air is mainly caused by a convection current due to a stack effect induced by the temperature difference between the tunnel air and the outside air.

Survey of 222Rn concentrations in the air of a tunnel located in Nagano City using the solid-state nuclear track detector method.

The survey of 222Rn concentration in the air of tunnels constructed during World War II has been performed using a solid-state nuclear track detector technique. For the practical application of this technique to the determination of 222Rn concentrations in air, some basic properties were experimentally examined on the cellulose nitrate film, Kodak LR 115 type II. The calibration coefficient of the cellulose nitrate film used is determined from a correlation between the 222Rn concentration in air and the observed number of perforated etched tracks for widespread radon concentrations. The slope of the linear relationship observed yields a calibration coefficient of (0.00209 +/- 0.00018) tracks cm(-2) (Bq m(-3) h)(-1). From the survey of 222Rn concentration in the air of tunnels, the concentration of several thousand Bq m(-3) was observed at the inner most area of the tunnel, and the seasonal variation was clearly observed. The exponential distribution of radon concentration as a function of distance from the openings of the tunnel suggests that the radon concentration in the tunnel is basically governed by diffusion and mixing of radon gas with air.

Indoor 222Rn levels and irradiation doses on the territory of Ukraine

Goal for the Ukrainian population of studies was determination of irradiation doses from 222Rn. More than 6000 measurements have been conducted by method of passive track dosimeter all over the country in houses of different architectural and planning solutions. Average indoor 222Rn concentrations were determined in different regions of Ukraine. Basic regularities were revealed for formation of radon levels. Average weighted population irradiation dose from 222Rn and evaluated in air of residential buildings which consisted 4.2 mSv per year. It is 79% of total irradiation dose from all the sources of natural radioactivity. Collective 222Rn doses were determined for majority of regions of Ukraine. The studies confirm necessity of efficient countermeasure's system development directed for decrease of 222Rn concentrations in air of premises. It will lead to diminishing of overall irradiation doses and, subsequently, radiation risks for health of the Ukraine population.

On the measurement of 218Po diffusivity using the two-filter method

Determining the diffusion coefficient of 218Po is an important application of the two-filter method (Thomas and LeClare, 1970, Hlth Phys. 18, 113). Air containing a known concentration of 222Rn is drawn through a cylindrical tube with filters at both ends. The 218Po activity on the downstream filter relative to the 222Rn concentration in air is interpreted to determine the diffusivity of 218Po. Previously, the interpretation scheme was based on a theoretical analysis of 218Po transport and production in a tube by Tan (1969, Int. J. Heat Mass Trans. 12, 471), and Tan and Hsu (1970, Int. J. Heat Mass Trans. 13, 1887). Their analysis did not account for radioactive decay of airborne 218Po within the apparatus nor for the perturbation of the fluid flow caused by the flow resistance of the downstream filter. Also, simplified analytical air flow profiles were assumed in that analysis. In this paper, the two-filter method is re-analyzed numerically, by solving the continuity equation, the Navier-Stokes equations and the species conservation equation for a tube. Full account is taken of the effects of radioactive decay of 218Po, and the flow resistance of the downstream filter. The results of the new analysis lead to a downward correction of reported diffusivities of 218Po by about 10–20%.

Relationships between 222Rn dissolved in ground water supplies and indoor 222Rn concentrations in some Colorado front range houses.

Indoor 222Rn concentrations were measured in 37 houses with alpha track detectors placed in water-use rooms near water sources (bathrooms, laundry rooms, and kitchens) and in non-water-use living rooms, dining rooms, and bedrooms away from water sources. Results show that relative contributions of 222Rn to indoor air from water use are insignificant when soil-gas concentrations are high but become increasingly important as the ratio of 222Rn-in-water: 222Rn-in-soil gas increases. High soil-gas 222Rn concentrations may mask 222Rn contributions from water even when waterborne 222Rn concentrations are as high as 750 kBq m-3. Ground water in Precambrian Pikes Peak granite averages 340 kBq m-3 222Rn, vs. 170 kBq m-3 in Precambrian migmatite, but average 222Rn concentrations in soil gas are also lower in migmatite. Because the ratio of 222Rn-in-water: 222Rn-in-soil gas may be consistently higher for houses in migmatite than in Pikes Peak granite, indoor air in houses built on migmatite may have a greater relative contribution from water use even though average 222Rn concentrations in the water are lower. Continuous monitoring of 222Rn concentrations in air on 15-min intervals also indicates that additions to indoor concentrations from water use are significant and measurable only when soil-gas concentrations are low and concentrations in water are high. When soil-gas concentrations were mitigated to less than 150 Bq m-3 in one house, water contributes 20-40% of the annual indoor 222Rn concentration in the laundry room (222Rn concentration in water of 670 kBq m-3). Conversely, when the mitigation system is inactive, diurnal fluctuations and other variations in the soil-gas 222Rn contribution swamp the variability due to water use in the house. Measurable variations in indoor concentrations from water use were not detected in one house despite a low soil-gas contribution of approximately 150 Bq m-3 because waterborne 222Rn concentrations also are low (80 kBq m-3). This result suggests that 222Rn concentrations in water near the recommended EPA limit in drinking water of 11 kBq m-3 may not contribute measurable amounts of 222Rn to indoor air in most houses.

A study of 222Rn in well water supplies in the area of Aberdeen, Scotland

222Rn concentrations in water supplies derived from wells have been determined in 70 houses in the area of Aberdeen. Supplies derived from igneous granite rock had 40–76 Bq litre −1, while those on metasedimentary rock had 3–35 Bq litre −1. Experiments performed while tap water was flowing demonstrated that the 222Rn concentration in air could be increased by several hundred Bq m −3. Factors related to 222Rn emanation rates were derived from fits of such data to theory. The contribution made by 222Rn from well water supplies to the annual effective dose equivalent was estimated to be 0.02–0.4 mSv. This was only 1–5% of the total dose from 222Rn in the atmosphere in the houses studied.

Location of groundwater seepage points into a river by measurement of 222Rn concentration in water using activated charcoal passive collectors

A new method to measure 222Rn concentration in water is described. This method is an application of the activated charcoal passive collector method, which is sometimes used for measurement of 222Rn concentration in air. The model and the equation which express the quantity of 222Rn adsorbed in activated charcoal in the collector were constructed, inspected experimentally, and proved to work well enough for the measurement of relative concentration of 222Rn in water. We used this method to measure the 222Rn concentration in water at ∼ 20 points in an actual river. Based on the fact that the concentration of 222Rn in ground water is generally much higher than that of surface water, we found several possible groundwater seepage points along the river. For the absolute measurement of 222Rn concentration in water by this method, it would also be necessary to investigate the effect of temperature on the quantity of 222Rn collected in a collector.

Preliminary experiences with 222Rn gas in Arizona homes.

Results of a survey of 222Rn gas using four-day charcoal canister tests in 759 Arizona homes are reported. Although the study was not random with respect to population or land area, it was useful in identifying areas at risk and locating several homes having elevated indoor 222Rn air concentrations. Approximately 18% of the homes tested exceeded 150 Bq m-3 (4 pCi L-1), with 7% exceeding 300 Bq m-3 (8 pCi L-1). Several Arizona cities had larger fractions of homes exceeding 150 Bq m-3 (4 pCi L-1), such as Carefree and Cave Creek (23%), Paradise Valley (30%), Payson (33%), and Prescott (31%). The Granite Dells and Groom Creek areas of Prescott had in excess of 40-60% of the houses tested exceeding 150 Bq m-3 (4 pCi L-1). Elevated 222Rn concentrations were measured for a variety of home types having different construction materials. Private well water was identified as a potentially significant source of 222Rn gas in Prescott homes, with water from one well testing over 3.5 MBq m-3 (94,000 pCi L-1). A 222Rn concentration in air exceeding 410,000 Bq m-3 (11,000 pCi L-1) was measured using a four-day charcoal canister test in a house in Prescott which had a well opening into a living space. Additional measurements in this 150-m3 dwelling revealed a strikingly heterogeneous 222Rn concentration. The excessive 222Rn level in the dwelling was reduced to less than 190 Bq m-3 (5.2 pCi L-1) by sealing the well head with caulking and providing passive ventilation through a pipe.