Measuring radon exhalation rate by tracing the radon concentration of ventilation-type accumulation chamber

Radon exhalation rate is crucial in the estimation of radiation risk from various materials. RAD7 only focus on the count of the ²¹⁸Po in sniff mode, and is well suited to measure radon exhalation rates. This paper presents a fast method for measuring radon exhalation from medium surface with a ventilation-type accumulation chamber by the RAD7 while making the effects of leakage and back diffusion negligible. The radon exhalation rate can be obtained from the measured values before radioactive equilibrium between Radon and progeny occurs. This method is based on the principle for tracing radon concentration changes by deriving ²²²Rn concentrations through ²¹⁸Po measurements. Several radon exhalation rate measurements of medium surface have been performed in the Radon Laboratory of the University of South China. The radon exhalation rates obtained by verification experiments are within the accepted values for the reference value.     

Measurement of radon in air using a radon-218Po calibration curve determined by an absorptive non-volatile liquid scintillator

This work reports a novel method for determining ²²²Rn (radon) in air using a radon-²¹⁸Po calibration curve constructed by an absorbable non-volatile liquid scintillator (NVLS). The ability of this method to detect low natural concentrations of radon was confirmed from linear extrapolation of the curve between 500 and 8000 Bq/m³. The calibration curve was created from data obtained from measurements performed in a radon calibration chamber at the National Institute of Radiological Science (NIRS) by using the least-squares method. The line had high precision and stability, and the required detection time was less than that of ²¹⁴Po. An absorptive NVLS was used to collect radon and was found to be highly advantageous for α-spectrometry liquid scintillation measurements. Variations of the Ostwald coefficient due to changes in temperature and humidity, which affect radon absorption, were investigated and discussed.     

Determination of radon concentration in soil gas by gamma-ray spectrometry of olive oil

Measurements of radon concentration in soil gas have been carried out using a bubbling system in which the soil gas is drawn through an active pumping to bubble a liquid absorber (olive oil) for the deposition of the soil gas in it. After the bubbling process, the absorber is then taken for gamma-ray measurements. Gamma-ray photopeaks from the ²¹⁴Pb and the ²¹⁴Bi radon progeny are considered for the detection of the ²²²Rn gas to study the concentration levels for radon soil gas. Results for some field measurements were obtained and compared with results obtained using AlphaGuard radon gas monitor. The technique provides a possible approach for the measurements of radon soil gas with gamma-ray spectrometry.     

Measurements of the size distribution of unattached radon progeny by using the imaging plate

The size distribution of unattached radon progeny is an important parameter for an accurate estimation of the internal dose of radon exposure. In this study, a new measuring system was developed to evaluate the size distribution of unattached radon progeny in air. In the system, airborne radon progeny were collected with a newly designed graded screen array (GSA), the activity concentrations were measured by using the imaging plate technique, and the size distribution of unattached fraction was retrieved by using an iterative nonlinear algorithm. The simulation results indicated that the collection characteristics of the new GSA system were well agreed with other systems. Test experiments showed that the activity-weighted median diameters (AMD) for unattached ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi were 0.89 ± 0.11 nm, 0.96 ± 0.13 nm and 1.01 ± 0.25 nm in a particle-free radon chamber, and the distribution changed with different concentrations of particles. As multiple measurements can be simultaneously carried out with a single IP, the new technique is considered as an optional and useful way to measure the size distribution measurement of unattached radon progeny.     

Measurement of the Po concentration in air using makrofol-de detectors

The measurement of the ²¹⁴Po concentration in air with Makrofol-DE detectors is useful to estimate the long-term averaged equilibrium factors indoors. To differentiate α-particles emitted by ²¹⁴Po from those emitted by ²¹⁸Po and ²²²Rn, the detector must register only α-particles with energies between 6.2 and 7.5 MeV. The required energy response is obtained only if a removed layer of about 43 μm is achieved in a chemical etching of the detector. The methodology used to determine the etching conditions is described in this paper. The optimum conditions found are: a) chemical etching for 6 h at a temperature of 40°C, using 7.5 M KOH mixed with 50% ethanol as an etchant, and b) electrochemical etching for 1 h at a frequency of 3 kHz and an electric field strength of 34 kV cm⁻¹. Several dosimeters have exposed during 2 months in dwellings located in the Barcelona area, Spain. A ²¹⁴Po averaged concentration of (13.6 ± 8.6) Bq m⁻³ was obtained.     

Zum Gammaspektrum von214Po(RaC′)

A high-resolution gamma-ray spectrometer with a Ge(Li)-detector is described. The spectrometer is used as a single crystal spectrometer as well as a three crystal pair spectrometer with a Ge(Li) central detector and two NaJ-crystals for the detection of the annihilation quanta. Measurements were made of²¹⁴Po. The sources were²²²Rn in small glass tubes. 66 gamma-rays, 10 of which hitherto unknown, were observed. An improved level scheme of²¹⁴Po is given.     

Simultaneous measurement of radon, radon progeny and thoron concentrations using Makrofol-DE detectors

In this study we describe the set-up of a new passive integrating system to measure simultaneously ²²²Rn, ²²²Rn progeny (²¹⁸Po and ²¹⁴Po) and ²²⁰Rn concentration indoors. It consists of four Makrofol-DE (polycarbonate) circular foils. Two are enclosed within two diffusion chambers—each one with a different filter membrane—to measure ²²²Rn and ²²²Rn+²²⁰Rn. The other two foils are kept in direct contact with air and are electrochemically etched at different conditions to obtain the ²²²Rn daughters. Theoretical sensitivities of each Makrofol-DE foil are calculated using Monte-Carlo technique. The calculations are performed taking into account: (1) the Bethe–Bloch's expression for the stopping power of heavy charged particles in a medium, (2) the properties and behaviour of ²²²Rn, ²²⁰Rn and their progeny in the open air and within the diffusion chamber and (3) the etching conditions used to visualise -particles tracks.     

222Rn activity in soil gas across selected fault segments in the Cantabrian Mountains,NW Spain

²²²Rn activity in soil gas was measured across fault segments of the seismic active Ventaniella Fault and the seismic inactive Sabero-Gordón Fault in the Cantabrian Mountains, NW Spain, in order to investigate the variability of the ²²²Rn concentration. The sampling took place in summer and autumn 2010. During the autumn measurement program, an additional ²²²Rn soil gas mapping was carried out in the Sabero-Gordón research area. Zones of elevated ²²²Rn activity in the soil gas were identified by background ²²²Rn values of the geological formations used for mapping and local background values from ²²²Rn values outside the elevated ²²²Rn activity zones. Unexpectedly, the Sabero-Gordón Fault showed higher ²²²Rn activity, up to 441 kBqm^?3, compared to the ²²²Rn activity of the Ventaniella Fault which had a maximum of 106 kBqm^?3. Comparison of the results shows that the values measured in summer are about 5 times higher than the autumn values. This difference is not reflected in petrophysical soil parameters or meteorological conditions documented during the field measurements. Based on the results of our work we conclude that the magnitude of ²²²Rn concentration in soil gas is not an indicator of local seismic activity of the investigated faults. For the studied segment of the aseismic Sabero-Gordón Fault we suggest active genesis of pathways for gas migration driven by aseismic fault slip causing the elevated ²²²Rn activity in soil gas.     

Exhalation of radon and its carrier gases in SW Taiwan

Gas compositions of mud volcanoes reveal multiple sources for gas exhalation in SW Taiwan. For comparison, two sites, Yan-chao (YC) and Chung-lun (CL), were chosen for measurements of soil Rn concentrations using a portable radon detector. The ²²²Rn concentrations at the YC site were ca. 5200 Bq/m³. However, the average ²²²Rn concentrations at the CL site exhibited higher value of ca. 16,800 Bq/m³. With the reference of the gas flux and compositions from the nearby mud pool, the soil ²²²Rn concentrations are largely controlled by the flux of carrier gases exhaled from deep reservoirs.     

<Superscript>210</Superscript>Pb and <Superscript>210</Superscript>Po determination in environmental samples using liquid scintillation counting and alpha spectrometry

A simple radiochemical procedure has been developed to determine ²¹⁰Pb and ²¹⁰Po in environmental samples from the same matrix. Sediment samples are decomposed by leaching with mineral acids or by microwave digestion, while water samples are pre-concentrated. One part of the resulting solution, spiked with ²⁰⁹Po, is used for ²¹⁰Po determination by spontaneous deposition onto nickel disks (α-spectrometry). The other part is assayed for ²¹⁰Pb, separating the Pb either by anion-exchange (sediment samples), or by solvent extraction (water samples). The ²¹⁰Pb source is finally prepared by precipitation as oxalate and the chemical recovery determined by gravimetry. The ²¹⁰Pb activity concentration is determined by liquid scintillation. A standard sediment sample supplied by IAEA and spiked water samples were analysed to check the procedure. The ²¹⁰Pb and ²¹⁰Po measurements agreed well with the certifications, deviations being less than 10%. The mean recoveries for Pb and Po were (70±12)% and (77±8%) for sediments, and (70±10)% and (81±7)% for waters, respectively.     

Thoron (220Rn) in the indoor environment and work places

Ever since studies on uranium miners established the presence of a positive risk coefficient for the occurrence of lung cancer in miners exposed to elevated levels of ²²²Rn and its progeny, there was a great upsurge of interest in the measurement of ²²²Rn in the environment. Subsequently, considerable data is being generated on the levels of ²²²Rn in the environment across the worlds and is being periodically reported by UNSCEAR reports. In contrast to this, data pertaining to ²²⁰Rn in indoors and workplace environment is scaree due to the genral perception that its levels are negligible due to its shorter half life, and subsequently its contribution to the total inhalation dose is ignored, in the presence of other significant sources of natural radiation. This may not be true. Globally many locations have higher levels of natural background radiation due to elevated levels of primordial radio nuclides in the soil and their decay products like radon (²²²Rn), and thoron (²²⁰Rn) in the environment. Of late, technologically enhanced naturally occurring radioactive material has also contributed to the burden of background radiation. It is estimated that inhalation of ²²²Rn, ²²⁰Rn and their short lived progenies contribute more than 54% of the total natural background radiation dose received by the general population. ²²⁰Rn problem exists in industries which use thorium nitrate. Including India, lamps using thoriated gas mantles are still being used for indoor and outdoor lighting and by hawkers in rural as well as urban areas. Considering the fact that large amount of thorium nitrate is being handled by these industries, contribution to the inhalation dose of workers from ²²⁰Rn gas emanated and build up of the progeny in ambient air may also be quite significant. In this paper current status of ²²⁰Rn levels in the indoor environment and workplaces as well as in other industries where large amount of ²³²Th is being handled is being summarized. Methods of measurement and reported levels are also summarized.     

A new pin-hole discriminated 222Rn/220Rn passive measurement device with single entry face

Solid State Nuclear Track Detector (SSNTD) based diffusion chambers have been widely used for residential radon measurements due to their cost effectiveness, portability and easy-to-use feature. In India, an LR-115 track detector based twin-cup dosimeter has been in use for about a decade for indoor ²²²Rn and ²²⁰Rn measurements. However, the estimation of the gas concentrations using this dosimeter was based on the assumption of the same entry rate of the gases into the two cups of the dosimeter, which may not be valid for dosimeters deployed in turbulent environmental conditions. To overcome this limitation, a new pin-hole based ²²²Rn/²²⁰Rn discriminating measurement device has been developed. The underlying discrimination technique has been established by modelling ²²²Rn and ²²⁰Rn diffusion into a pin-hole chamber and validating the same by carrying out experiments in a test chamber. The device has been calibrated at Bhabha Atomic Research Centre, Mumbai following the standard procedures to correlate the number of tracks registered in the LR-115 detector placed in the two chambers to the ²²²Rn and ²²⁰Rn concentration in the environment. Salient features of the device include (i) the pin-holes act as ²²²Rn/²²⁰Rn discriminator and eliminate the requirement of membrane filter used in the earlier twin cup design (ii) the single entrance design for gas transmission and (iii) use of multiple pin-holes of reasonably small radius minimises effect of turbulence on ²²²Rn/²²⁰Rn transmission factors so that the calibration factor is independent of indoor turbulence.     

大气颗粒物滞留时间的确定方法及初步实验验证

通过研究大气颗粒物中222Rn子体活度比与颗粒物平均寿命之间的关系,建立了基于活度比估算大气颗粒物滞留时间(residence time of atmospheric aerosol,RTAA)的方法,并在相对理想条件下进行了实验验证.当氡室浓度稳定为1.816kBq/m3时,由214Bi/214Pb活度比计算出的RTAA为112.17min,与氡室的平均换气时间(104.17min)相当,表明大气颗粒物中同一衰变链上的放射性核素活度比(如214Bi/214Pb,210Bi/210Pb或210Po/210Pb)可以用于估算RTAA.     

Traceability of CDs/DVDs used as retrospective 222Rn detectors to reference STAR laboratory

The practical applications of the method for retrospective ²²²Rn measurements by home stored CDs/DVDs need a proper metrological assurance. The specific feature of this method, as compared to other methods for retrospective ²²²Rn measurements is the possibility for an individual a posteriori calibration of the used CD/DVD-detectors. This paper describes a procedure to ensure the traceability of this method to a reference STAR laboratory. A set of 7 groups of CDs/DVDs were exposed to 4 reference ²²²Rn exposure levels. After that they were treated in the etching laboratory as ”real” detectors and the ²²²Rn concentrations were determined by applying an individual a posteriori calibration, correction for high track density and correction for depth at which the alpha tracks were etched. The results from all 7 groups of exposed detectors demonstrated relative variation from the reference values in the interval 3.4–23.4%. The results provide evidence that the routine measurements by the CD/DVD method warrant measurements with a relative uncertainty better than 25% and therefore this method is acceptable for large-scale applications.     

Radon loss from encapsulated sediments in Ge gamma-ray spectrometry for the annual radiation dose determination in luminescence dating

In Ge gamma-ray spectrometry for the annual radiation dose determination in the luminescence dating of sediments, the picture of ²²⁶Ra enrichment or depletion (in the ²³⁸U decay series) obtained via measurement of its ²¹⁴Pb and ²¹⁴Bi daughters may be disturbed by the ²²²Rn-content of the sample being decreased due to manipulations such as drying and pulverizing. Therefore, it is common practice to start the measurement only about 1 month after encapsulating the material, after which the ²²⁶Ra(1600 a)- ²²²Rn(3.82 d) mother-daughter equilibrium is re-established. Evidently, this only holds on condition that no significant escape of Rn occurs out of the sediment after making it up for counting. In order to experimentally investigate this effect, in the present work measurements were carried out with various types of dried and pulverized sediments that were either encapsulated in screw-cap polystyrene vials or in sealed glass containers, or that were mixed with molten wax followed by solidification in a cylindrical geometry. From the results obtained, it could be concluded that preparation and counting of the sediment-wax mixture is the method of choice.     

Seasonal variations of radon and the radiation exposure levels in Nerja cave, Spain

²²²Rn concentrations in the air in Nerja cave (Spain) (3° 52′35′′W 36° 43′50′′N) were measured by continuous monitoring using Alpha-Guard, Genitron instrument equipment. The ²²²Rn measurements were carried out for a complete annual cycle in the different halls: Vestibule hall from July 2003 to June 2004, Ballet hall from July 2004 to June 2005 and Mirador hall from July 2005 to June 2006. Starting from the entrance of the cave we successively find the Vestibule hall, the Ballet hall and the Mirador hall. The range of ²²²Rn levels were of 8–627 Bq m⁻³ for the Vestibule hall, 28–575 Bq m⁻³ for the Ballet hall and 38–578 Bq m⁻³ for the Mirador. The aim of this study was to detect seasonal variation patterns of ²²²Rn concentrations. The seasonal variations of ²²²Rn concentrations are discussed in relation to various meteorological factors measured inside and outside the cave. The radiation exposure levels for workers and tourists with different equilibrium factors have been evaluated. The radiation exposure levels for workers and tourists only represent a low percentage of the exposure guides for the general population.     

Verification of radioactive equilibrium to discriminate radon and progeny with LR 115 under a thin film geometry

A system of image analysis is applied to the track analysis of a plastic detector (LR 115). Based on track characteristics the system permits the separation of tracks produced by ²²²Rn and ²¹⁸Po from those produced by ²¹⁴Po. LR 115 was used inside a thin film geometry monitor and irradiated under very low ventilation conditions, where secular radioactive equilibrium between radon and progeny is expected. The monitor is used intending to exclude the entrance of external radon progeny in the sensitive volume of the plastic detector. The radioactive (secular) equilibrium is rapidly attained inside the monitor and equal numbers of particles from ²¹⁸Po, ²¹⁴Po and ²²²Rn are expected to reach the plastic. In order to guarantee good detection efficiency in the restricted volume, and to discriminate alpha energies, the LR 115 piece inside the monitor is covered with an aluminum foil of suitable thickness. The separation of tracks produced by alpha particles of different energies is made through the use of two track parameters related to area and opacity of the tracks. The ratio of tracks produced by (²¹⁸Po and ²²²Rn) and ²¹⁴Po—expected as two—is used to test the separation method in a series of controlled irradiations. Results point to the experimental attainment of radioactive equilibrium inside the monitor supporting the determination of ²¹⁴Po concentration alone, and points to an exclusive entrance of ²²²Rn inside the monitor, at low ventilation rates. This way, in situations where radioactive equilibrium inside the monitor may be considered, the exclusive measurement of radon concentration in the environment is possible.     

Atmospheric 222Rn concentration and source term at El Arenosillo 100 m meteorological tower in southwest Spain

²²²Rn concentration time series at 10 m and at 100 m have been measured hourly for one year at the meteorological station, El Arenosillo, on the Spanish southwest coast. A ²²²Rn flux characterization was also done.A seasonal analysis of atmospheric ²²²Rn concentration was performed and results for each season present evidence associated with the origin of air masses reaching the El Arenosillo station. An increase in ²²²Rn concentration was observed when the wind came from Morocco, the Sierra Morena and the Guadalquivir valley areas. On the other hand, a net ²²²Rn concentration decrease was found when the wind came from the Atlantic Ocean and the South of Portugal.Low ²²²Rn flux of 4 Bq m^?2 h^?1 was measured. This result makes this station a useful site for studies related to remote ²²²Rn source contributions because of low local ²²²Rn background. The measured annual average concentration of ²²²Rn gas at the El Arenosillo station is 3.51 ± 0.05 Bq m^?3 at 10 m and 2.61 ± 0.05 Bq m^?3 at 100 m.     

Po and Pb concentration of cigarettes traded in Hungary and their estimated dose contribution due to smoking

It is known that tobacco leaves may contain ²¹⁰Pb and ²¹⁰Po in significant concentrations. The cumulative alpha-radiation dose due to the radioactive content of inhaled cigarette smoke and the increasing number of lung cancer cases explain the importance of the investigation. The present study investigated the activity concentrations of these two radionuclides in 29 Hungarian cigarette samples. The relation between ²¹⁰Po/²¹⁰Pb activity and nicotine/tar content of these cigarettes was also examined. ²¹⁰Po was determined by alpha spectrometry using a PIPS detector after chemical leaching and spontaneous deposition of ²¹⁰Po on a high nickel-content (25%) stainless steel disk. The ²¹⁰Pb activity was calculated from the ²¹⁰Po originated from the decay of ²¹⁰Pb after a waiting period of eight months. The ²¹⁰Po activity concentrations of the measured types of cigarettes ranged from 10.0 to 33.5 mBq/cigarette, and the activity of ²¹⁰Pb varied from 9.6 to 32.5 mBq/cigarette. The average annual committed effective dose is estimated to be $185.6\pm 70.6\mathrm{\mu }\mathrm{Sv}/\mathrm{y}$ and $58.7\pm 22.7\mathrm{\mu }\mathrm{Sv}/\mathrm{y}$ due to cigarette smoking (20 cigarettes/day) for ²¹⁰Po and ²¹⁰Pb, respectively.