Time-efficient method for the determination of 210Pb, 210Bi, and 210Po activities in seawater using liquid scintillation spectrometry

A novel method has been developed for determining the natural decay series radionuclides (NDS), 210Pb, 210Bi, and 210Po, in seawater by way of state-of-the-art liquid scintillation spectrometry. For 210Pb analysis, the method makes use of a 212Pb yield tracer, prepared by ion exchange separation from aged Th(NO3)4. 210Bi recovery is determined using 207Bi as the yield tracer, and 210Po is determined using the conventional 208Po yield tracer. The limits of detection for this method are 0.32, 0.34, and 0.004 mBq 1-1 for 210Pb, 210Bi, and 210Po, respectively. The analysis can be completed within 10 days, as compared with up to one year for traditional methods. Results are presented for a preliminary study of 210Pb, 210Bi, and 210Po in the dissolved and particle-bound phases of Irish Sea water.     

Radon progeny in hydrometeors at the earth's surface

During atmospheric thermal inversions, dew and hoarfrost concentrate gamma emitting radionuclides of the short-lived (222)Rn progeny ((214)Pb and (214)Bi), causing an increase in the total natural gamma background from the ground. To highlight this phenomenon, a volcanic zone of high (222)Rn flux was studied during the winter season 2010-11. High-specific short-lived radon progeny activities up to 122 Bq g(-1) were detected in hydrometeors forming at the earth's surface (ESHs), corresponding to a mean increase of up to 17 % of the normal gamma background value. A theoretical model, depending on radon flux from soil and predicting the radon progeny concentrations in hydrometeors forming at the ESHs is presented. The comparison between model and field data shows a good correspondence. Around nuclear power plants or in nuclear facilities that use automatic NaI or CsI total gamma spectroscopy systems for monitoring radioactive contamination, hydrometeors forming at the ESHs in sites with a high radon flux could represent a relevant source of false alarms of radioactive contamination.     

Influence of radioactive aerosol and biological parameters of inhaled radon progeny on human lung dose

The present work focuses on assessing the influence of biological and aerosol parameters on human lung dose. The dose conversion factor (DCF), which gives the relationship between the effective dose and the potential alpha energy concentration of inhaled short-lived radon progeny (218Po, 214Pb, 214Bi/214Po) is estimated using a dosimetric approach related to the International Commission on Radiological Protection(ICRP). The calculations are based on the measurements of the distribution of activity size of indoor radon progeny, their unattached fraction (f(b)) and potential alpha energy concentration (E). These experimental data are measured using a low-pressure cascade impactor and a wire-screen diffusion battery. Because of the short half-lives of the investigated nuclides, modifications that simplify the dose calculation are possible. The radioactive aerosol and biological parameters are varied in order to assess the DCF arising from the uncertainty of these parameters. The main emphasis is on the variation of the ventilation rate, breathing mode, critical cells for the induction of lung cancer and the parameters of the attached and unattached activity size distribution of the radon progeny. The investigation shows that the DCF is more than a factor of two higher than the values recommended by the ICRP, namely 3.9 mSv WLM(-1) for the public and 5.1 mSv WLM(-1) for working places. The dose results for indoor aerosol conditions are in the range 2.3-2.6 mSv WLM(-1) depending on the breathing mode.     

Radon progeny in Egyptian underground phosphate mines

In addition to the workers in uranium mines, the staff of other underground mines, such as workers in underground phosphate mines, can be exposed to 222Rn and its progeny. In this study the individual radon progeny concentrations were measured in three Egyptian underground phosphate mines to estimate the occupational exposure of the workers at those sites. A filter method was used to measure individual radon progeny concentrations (218Po, 214Pb and 214Po). The reported mean values of radon progeny concentrations exceed the action levels which are recommended by ICRP 65 (1993). Based on the measured individual radon progeny concentrations (218Po, 214Pb and 214Po) in these mines, the annual effective dose for the workers has been calculated using the lung dose model of ICRP 66 (1994). According to the obtained results, some countermeasures were recommended in this study to minimise these exposure levels.     

Fraction of the positive 218Po and 214Pb clusters in indoor air

The fraction of the positively charged unattached radon decay products, 218Po and 214Pb in indoor air was determined by model calculations. The results of the calculations were confirmed by measurements in a test chamber (volume: 8 m3). The fraction of both radionuclides depends on the attachment parameter (S(1)) and the neutralisation rate (nu) in room air. The total removal parameter S1 = lambda1 + v + q(f) + X = lambda1 C1f/C0 considers the attachment rate to aerosol particles (X), plate-out rate to room surfaces (q(f)) and the ventilation rate (nu) (lambda1: decay constant of 218Po). The S1-value of room can be determined by measurement of the concentration of the unattached 218Po clusters (C1f) and radon (C0). The neutralisation rate (nu) in environmental air depends mainly on the ion production rate. The influence of the relative humidity in the range 30-95% (temperature: 20 degrees C) is negligible. In addition, equal neutralisation rates for 218Po and 214Pb could be derived. In room air with ion production rates between 5 and 500 nC kg(-1) h(-1) mainly generated by the alpha emitters of radon, thoron and their short-lived decay products, the fractions for positive 218Po clusters vary between 55 and 17% and for 214Pb clusters between 53 and 14%. For a typical average concentration of radon (50 Bq m(-3)) and thoron (10 Bq m(-3)) in homes, 48% of 218Po clusters and 45% of 214Pb clusters are positively charged.     

In vivo measurement of unattached radon progeny deposited in the human respiratory tract

Seven nose breathing and seven mouth breathing volunteers were exposed to atmospheres enriched with unattached radon progeny (218Po, 214Pb and 214Bi). The activity of these radionuclides deposited in the respiratory tract was measured in vivo after the exposures. The results of these measurements are in agreement with predictions calculated with the ICRP Publication 66 Human Respiratory Tract Model. Temporal analysis of the activity deposited in the heads of the volunteers leads to the conclusion that a significant amount of the deposited activity associated with particle diameters of about 1 nm is not subject to a fast transport to the gastrointestinal tract as generally reported for larger aerosol particles.     

Radioactivity of 210Pb in Japanese cigarettes and radiation dose from smoking inhalation

It is well known that cigarette tobaccos contain naturally occurring radioactive nuclides such as (210)Pb and (210)Po. In many countries, the radioactivity of tobaccos has been measured to estimate the effective dose from smoking inhalation. The present study covered 24 cigarette brands including the top 20 of sales in Japan between April 2008 and March 2009. The activity concentrations of (210)Pb were measured by gamma-ray spectrometry, and then those of its progeny ((210)Po) were evaluated assuming the radioactive equilibrium between the two nuclides. Their concentrations were in the range of 2-14 mBq cigarette(-1) with an arithmetic mean of 8±3 mBq cigarette(-1). The annual committed effective doses were also calculated, based on the scenario that a smoker consumes 20 cigarettes a day. The average doses from (210)Pb and (210)Po inhalations were 22±9 and 68±27 μSv y(-1), respectively.     

Influence of variability of 214Pb recoil factor on lung dose

Different parameters enter models of the human respiratory tract. The unattached fraction of the radon progeny was identified as the most important parameter, with the strongest influence on lung dose. The unattached fraction depends on the indoor aerosol concentration and other environmental conditions. The recoil factor, p, which influences the unattached fraction of 214Pb and 214Bi, defined as the average detachment probability from the aerosol after an alpha decay of 218Po, has almost always been taken as a constant. Here the recoil factor was recalculated under different assumptions and found to be in the range between 0.1 and 0.8. A smaller recoil factor means lower unattached fractions of 214Pb and 214Bi. The influence of the recoil factor on lung dose was also estimated. The lung dose is smaller by about 10% if p = 0.1 is assumed in calculating the unattached fraction instead of p = 0.8.     

Short-lived alpha sources of energies 6.0 MeV and 7.69 MeV for calibration purposes

An approach for preparation of short-lived alpha sources of energy 6.0 MeV and 7.69 MeV is proposed. The sources are prepared by taking a sample of 222Rn progeny on an alpha spectrometric filter. The activities (or related parameters) of 218Po, 214Pb and 214Bi at the end of sampling are precisely determined by a reference measurement with an alpha spectrometer. Further they are used as input values to calculate with a sufficient precision the number of emitted alpha particles of any energy and at any time interval of interest. Theoretical modelling and experimental results demonstrated that such sources could be prepared with a sufficient purity. There is a potential for the number of alpha particles emitted in a given time interval to be certified with an accuracy of 1-2%.     

Characterisation of an electronic radon gas personal dosemeter

The monitoring of radon exposure at workplaces is of great importance. Up to now passive measurement systems have been used for the registration of radon gas. Recently an electronic radon gas personal dosemeter came onto the market as an active measurement system for the registration of radon exposure (DOSEman; Sarad GmbH, Dresden, Germany). In this personal monitor, the radon gas diffuses through a membrane into a measurement chamber. A silicon detector system records spectroscopically the alpha decays of the radon gas and of the short-lived progeny 218Po and 214Po gathered onto the detector by an electrical field. In this work the calibration was tested and a proficiency test of this equipment was made. The diffusion behaviour of the radon gas into the measurement chamber, susceptibility to thoron, efficiency, influence of humidity, accuracy and the detection limit were checked.     

Measurement of radon diffusion in polyethylene based on alpha detection

Radon diffusion in different materials has been measured in the past. Usually the diffusion measurements are based on a direct determination of the amount of radon that diffuses through a thin layer of material. Here we present a method based on the measurement of the radon daughter products which are deposited inside the material. Looking at the decay of ²¹⁰Po allows us to directly measure the exponential diffusion profile characterized by the diffusion length. In addition we can determine the solubility of radon in PE. We also describe a second method to determine the diffusion constant based on the short-lived radon daughter products ²¹⁸Po and ²¹⁴Po, using the identical experimental setup.Measurements for regular polyethylene (PE) and High Molecular Weight Polyethylene (HMWPE) yielded diffusion lengths of (1.3±0.3) mm and (0.8±0.2) mm and solubilities of 0.5±0.1 and 0.7±0.2, respectively, for the first method; the diffusion lengths extracted from the second method are noticeably larger which may be caused by different experimental conditions during diffusion.     

Preparation of a 210Pb target

After an ion-exchange separation of ²¹⁰Pb from its daughters ²¹⁰Bi and ²¹⁰Po, a ²¹⁰Pb target has been electrodeposited on a carbon film. We describe the different steps of the target preparation, keeping in mind that ²¹⁰Pb is a highly radioactive isotope and that consequently the techniques must be efficient. The sandwiched target finally obtained has the following configuration: C (10 μg/cm²)+ ²¹⁰Pb (about 500 μg/cm²) + C (15 μg/cm²) mechanically protected with a beam-evaporated collodion film.     

Development of new analytical method based on beta-alpha coincidence method for selective measurement of 214Bi-214Po-application to dust filter used in radiation management

The radionuclide pair (214)Bi and (214)Po which belongs to the uranium series interferes with airborne radionuclide measurement needed for the radiation management of a nuclear facility. Time intervals between (214)Bi (β) and (214)Po (α) are much shorter than artificial radionuclides due to the short half-life of (214)Po (164 μs). The purpose of this study is to develop of a new analytical method (time interval analysis: TIA) based on the beta-alpha coincidence method for selective measurement of (214)Bi-(214)Po. The developed method was applied to an actual dust-filter measurement. The TIA system was highly effective in measuring of the filter with background subtraction.     

Natural radioactivity in tap waters of Eastern Black Sea region of Turkey

In this study, the activity concentrations of some radionuclides in tap water samples of the Eastern Black Sea region of Turkey were measured. The activity concentrations of radionuclides (214)Pb, (214)Bi, (40)K, (226)Ra and (137)Cs were determined using high resolution gamma ray spectrometry. Furthermore, (222)Rn activity concentrations in tap water samples were measured using Liquid Scintillation Counting. The mean specific activities of (214)Pb, (214)Bi, (226)Ra, (40)K, (137)Cs and (222)Rn in tap water samples were 6.73, 6, 19.16, 168.57, 5.45 mBq l(-1) and 10.82 Bq l(-1), respectively. These values are comparable with concentrations reported for other countries. The effective doses were determined due to intake of these radionuclides as a consequence of direct consumption of tap water samples. The estimated effective doses were 6.878 x 10(-4) microSv y(-1) for (214)Pb, 4.800 x 10(-4) microSv y(-1) for (214)Bi, 3.916 microSv y(-1) for (226)Ra, 0.763 microSv y(-1) for (40)K, 0.052 microSv y(-1) for (137)Cs and 5.848 microSv y(-1) for (222)Rn.     

Contribution of 210Pb bremsstrahlung to the background of lead shielded gamma spectrometers

Lead, which is often used as a shielding material, contains ²¹⁰Pb (T_1/2=22.3 y). The 46.54 keV γ-intensity of ²¹⁰Pb can be easily reduced by an inner lining, but the bremsstrahlung caused by the β-decay of its daughter, ²¹⁰Bi, with a maximal electron energy of 1.16 MeV, will contribute to the gamma detector background. The spectrum of this bremsstrahlung is calculated by numerically fitting the β-spectrum and integrating the Koch–Motz formula. The absorption of the bremsstrahlung in the lead and detection efficiencies for the HPGe detector are calculated by the effective solid angle algorithm, using corrections for the photopeak/Compton ratio of cross-sections in Ge. By comparison with the measured background spectrum, it is shown that, for the lead with 25 Bq/kg of ²¹⁰Pb up to 500 keV of gamma spectrum, the bremsstrahlung contribution to the background is about 20% for our surface-based detector system. Also, we compared our calculations with a Monte Carlo simulation of another detector system with a shield containing 1 Bq/kg of ²¹⁰Pb and found that our analytical method gives a value of roughly two times higher than the Monte Carlo one for the total bremsstrahlung contribution. The quality of the analytical semi-empirical method is proved by the reasonable agreement with the experimental results published.     

Study on radon and radon progeny in some living rooms

In the first part of this work, the potential alpha energy concentration (PAEC) of radon progeny, the equilibrium factor (F), the activity concentration of 222Rn gas (Co) and the unattached fraction (fp), were determined in 15 living rooms at El-Minia City, Egypt. The activity size distribution of (214)Pb was measured by using a low pressure Berner impactor. Based on the parameters of that distribution the total effective dose through the human lung was evaluated by using a dosimetric model calculation of ICRP. An electrostatic precipitation method was used for the determination of 222Rn gas concentration. The mean activity concentration of 222Rn gas (Co) was found to be 123 +/- 22 Bq m(-3). A mean unattached fraction (fp) of 0.11 +/- 0.02 was obtained at a mean aerosol particle concentration (Z) of (3.0 +/- 0.21) x 10(3) cm(-3). The mean equilibrium factor (F) was determined to be 0.35 +/- 0.03. The mean PAEC was found to be 37 +/- 8.1 Bq m(-3). The activity size distribution of (214)Pb shows mean activity median diameter of 290 nm with mean geometric standard deviation (sigma) of 2.45. At a total deposition fraction of approximately 23% the total effective dose to the lung was determined to be approximately 1.2 mSv. The second part of this paper deals with a study of natural radionuclide contents of samples collected from the building materials of those rooms under investigation given in part one of this paper. Analyses were performed in Marinelli beakers with a gamma multichannel analyser provided with a NaI(Tl) detector. The samples have revealed the presence of the uranium-radium and thorium radioisotopes as well as (40)K. Nine gamma-lines of the natural radioisotopes that correspond to 212Pb, 214Pb, 214Bi, 228Ac, 40K and 208Tl were detected and measured. The activity concentrations of 226Ra, 232Th and 40K were determined with mean specific activities of 65 +/- 22, 35 +/- 12 and 150 +/- 60 Bq kg(-1), respectively. These activities amount to a radium equivalent (Ra(eq)) of 126 Bq kg(-1) and to a mean value of external hazard index of 0.34.     

Bioaccumulation of 210Po and 210Pb in cephalopods collected from Kudankulam (Southeastern coast of Gulf of Mannar, India) and assessment of dose in human beings

Activities of (210)Po and (210)Pb in various tissues of two common species of cephalopod molluscs (cuttlefishes) of Kudankulam coast were studied. Of all the tissues, (210)Po and (210)Pb were found accumulated more in the digestive gland, shell gland and intestine. Urotheuthis duvauceli accumulated more (210)Po and (210)Pb in certain organs when compared with Sepiella inermis. The activity ratio of (210)Po/(210)Pb fell within the range of 0.6-29.3 in the organs. The biological concentration factor for the organs ranged from 1.2×10(3) to 2×10(5) for (210)Po and 3.6×10(2) to 7.6×10(4) for (210)Pb. A significant variation in the accumulation of (210)Po and (210)Pb was noted between species, organs and seasons (p < 0.05). The whole-body internal dose rate due to (210)Po was 1.24 and 0.83 μGy h(-1) and it was 2×10(-3) and 3×10(-3) μGy h(-1) due to (210)Pb for both the species. The effective dose in humans due to (210)Po intake ranged from 96.3 to 376.6 μSv y(-1) and that of (210)Pb ranged from 35.2 to 105.7 μSv y(-1), respectively. The data generated will act as a reference database for these organisms of this coast in which a nuclear power station is under construction.     

Corona discharge in charge reduction electrospray mass spectrometry

Corona discharge is applied to charge reduction electrospray mass spectrometry for the analysis of complex mixtures of biological molecules. Recent work has described a method of charge reduction (reducing the charge states of analyte ions generated by the electrospray process) employing the radioactive isotope 210Po to produce neutralizing species. A variation to this approach is presented, in which charge neutralization is mediated by ions produced in a corona discharge. Varying the corona discharge voltage controls the current and the degree of charge reduction, providing predominantly singly charged ions that are detected by a commercial electrospray time-of-flight mass spectrometer. This technique provides charge reduction for the simplification of ESI spectra, without need for any radioactive material.     

PB-210 concentrations in cigarettes tobaccos and radiation doses to the smokers

Cigarette smoking is a source of radiation exposure due to the concentrations of natural radionuclides in the tobacco leaves. From the health point of view, measurement of (210)Pb and (210)Po contents in cigarette tobacco is important to assess the radiological effects associated with the tobacco smoking for the smokers. In the present study, activity concentrations of (210)Pb, which is a (210)Po precursor in the (238)U-decay series, were measured in cigarette tobaccos. Samples of nine different commonly sold brands of cigarette tobaccos were analysed by employing a planar high purity germanium (HPGe) low background detector. Activity concentrations of (210)Pb were measured from its gamma peak at 47 keV. Mean activity concentration of (210)Pb was measured to be 13 +/- 4 Bq kg(-1) from all samples analysed. The annual committed effective dose for a smoker and the collective committed effective dose corresponding to annual cigarettes production were estimated to be 64 +/- 20 microSv and 0.6 x 10(2) man-Sv, respectively.     

Bio-kinetics of radon ingested from drinking water

Previous studies have identified the stomach as the most significant organ for the dose from ingested radon. An important factor in dosimetric modelling is the rate of radon loss from the stomach. In the present study, two subjects who ingested radon-rich water were measured using a NaI(Tl) detector fixed over the stomach. The counting rates for 214Pb and 214Bi peak regions were plotted as a function of time after ingestion. These data were interpreted using a compartment model that expressed biokinetics of radon and its progeny. The model was fitted to the experimental data by changing biokinetic parameters such as the rate of radon loss from the stomach. Previous models for dosimetric purposes often assumed that the half-time for radon loss from the stomach is below 20 min. The present results, however, suggest that a part of radon stayed longer in the stomach than expected in the previous models.