Radon decay products activity measurement

Fig. 5.8. Relative activity size distribution in terms of potential alpha energy concentration, PAEC, of the unattached radon decay product clusters measured in a water supply station with high radon concentration and high humidity.

Possibly the most cost-effective method involves radon absorption on a small charge of activated charcoal that can be placed in an inexpensive polyethylene bag. The gamma-emitting radon decay products are measured by a scintillometer with an efficient collecting geometry, preferably approaching 4 TT. 

Commission of the European Communities., Results of the Second CEC Intercomparison of Active and Passive Dosemeters for the Measurement of Radon and Radon Decay Products, EUR Report 10403 EN (1986). ... 

Miles, J.C.H. and Sinnaeve, J., Results of the second CEC intercomparison of active and passive dosemeters for the measurement of radon and radon decay products (1984)... 

The subsoil is the principal source of radon in this house. Both the activity concentration of radium-226 in subsoil and of radon in soil gas are above levels for building ground that might result in significant indoor radon concentrations. The radon decay-product concentration in the dwelling before remedial measures were taken was substantially higher than the reference value of 120 mWL. 

The calculated size distribution of newly attached decay products is shown as curve C in Fig. 1.9. The activity median diameter is 0.16 /zm. With passage of time, the distribution would be shifted to larger particle sizes, as coagulation proceeds. George (1972) used diffusion batteries to measure the size distribution of nuclei carrying radon decay products and found activity median diameters (AMD) averaging 0.18,0.11, and 0.30 /um in a city basement, fifth floor room, and rural outside air, respectively. 

What can be done to combat radon pollution indoors The first step is to measure the radon level in the basement with a rehable test kit. Short-term and long-term kits are available (Figure 17.28). The short-term tests use activated charcoal to collect the decay products of radon over a period of several days. The container is sent to a laboratory where a technician measures the radioactivity (y rays) from radon-decay products lead-214 and bismuth-214. Knowing the length of exposure, the lab technician back-calculates to determine radon concentration. The long-term test kits use a piece of special polymer film on which an a particle will leave a track. After several months exposure, the film is etched with a sodium hydroxide solution and the num-... 

Gmndel and Porstendorfer (2004) showed that the long-lived radon decay products Pb and Po are almost all (93-96%) adsorbed on aerosol particles in the accumulation size range and only 4-7% of their activities are attached on nuclei with diameters smaller than 60 nm. AMAD-values of 558 nm for Pb and 545 nm for Po were measured, i.e. significantly larger values than those of the short-lived radon and thoron decay products. 

Using the data on radon decay product aerosols, Papastefanou and Bondietti (1991) reported a mean residence time, xr, of 8 days for aerosols of 0.3-pm activity median aerodynamic diameter (AMAD) size as determined from Bi/ Pb activity ratios. From the decay scheme of 2 Po T /2 = 3.05 min), because of the relatively short half-lives of the product radionuclides after two a-decays and two /S-decays, Pb-aerosols are produced. From 32 experiments for radon decay product aerosols ( °Pb-aerosols), Papastefanou and Bondietti (1991) calculated average values of fractions F and F2 of about 76.11 and 21.32, respectively. From 12 measurements of sulfate aerosols, Bondietti and Papastefanou (1993) calculated in the same manner average values of fractions F and F2 of about 68.67 and 12.63, respectively. According to Equation (4.12) and the above mentioned data, a mean residence time, xr, SO , of about 12 days would apply to sulfate aerosols of 0.3-pm mass median aerodynamic diameter (MMAD) size. 

Average values of the relative size distribution of the unattached radon decay products in terms of potential alj a energy concentration (PAEC). The measured values were approximated by a sum of i log-normal distributions, char-actmsed by the activity median aerodynamic diameter, AMAD, noted as AMDui, geometric standard deviation, Ogui. and activity fraction, fpvd- n = numba- of measurements Z = aerosol parhcle concentrations Cq = radon concentration RH = relative humidity... 

Besides cluster formation, the radon decay products attach to the existing aerosol particles within 1-100 s, forming the radioactive aerosols of the radon decay products. Results of the activity size distribution measurements carried out at different places in outdoor air, dwellings and workplaces are presented in Table 5.2. In general, the activity size distribution of the radon... 

The four-stage low-pressure cascade impactor incorporates both the impactor and wire screen methods (Tokonami et al., 1997). This system can measure the activity size distribution of radon decay products in a low level environment within 90 min. Figure 6.9 shows a block diagram of the activity-weighted size distribution instrument. In the first air inlet, unattached radon decay products are collected on a metal wire screen (300 mesh openings 118.2 cm wire diameter 3.75 x 10 cm). A silicon semiconductor detector, SSD, is set opposite the metal wire screens where both collection and detection are concurrent. Output signals from the silicon semiconductor detector are sent through a preamplifier, PA, and the internal amplifier of a multichannel analyser, MCA, and then to the multichannel analyser. 

Fig. 6.13. Measured and fitted activity size distributions of the short-lived radon decay products obtained by an online a-iintactor.

This paper deals with the plate-out characteristics of a variety of materials such as metals, plastics, fabrics and powders to the decay products of radon and thoron under laboratory-controlled conditions. In a previous paper, the author reported on measurements on the attachment rate and deposition velocity of radon and thoron decay products (Bigu, 1985). In these experiments, stainless steel discs and filter paper were used. At the time, the assumption was made that the surface a-activity measured was independent of the chemical and physical nature, and conditions, of the surface on which the products were deposited. The present work was partly aimed at verifying this assumption. 

The air containing the radon is passed into a chamber. After sufficient time for the decay products down to 214Po to reach equilibrium with radon, the activity is assessed from the ionisation current. To allow for radioactive contamination in the materials of the chamber, two identical chambers have been used, one filled with the radon-bearing air, the other with aged air, and with the ionisation currents opposed. Using steel chambers of 6.31 capacity, Hultqvist (1956) measured 4 Bq m-3 of 222Rn with 10% accuracy. 

Ifit is suspected that a radioactive materialhas been inhaled,measuring the activity fromno se swipes or in a tissue afterthe nose is blown can be used to confirm the inhalation. Measurement of radon concentrations in the breath is a technique that can be used if materials are inhaled which have radon as a decay product. Carbon-14 can be detected in exhaled breath as well. 

When an element has more than one radioisotope, determinations and data analysis are generally more complex because the isotopes may differ in half-life, especially when a series is involved, e.g., radium, thorium, polonium, radon, actinium, protactinium, and uranium. One possibility is to make measurements after the decay of the short-lived radionuclides, but this may require long waiting times. In favorable cases, it is more convenient to measure the activity of decay products (e.g., radon, thoron ( Rn), actinon ( Rn)), or correct the measurements of the short-lived radioisotopes after determination of the isotopic composition. 

The PAEC can be readily calculated once the activities of the individual radionuclides have been determined from measurements. Direct measurements of the concentrations of all short-lived decay products of Rn are difficult and limited. They are estimated from considerations of equilibrium (or disequilibrium) between Rn and its decay products. An equilibrium factor F is defined that permits the exposure to be estimated in terms of the PAEC from the measurement of radon gas concentration. This equilibrium factor is defined as the ratio of the actual PAEC to the PAEC that would prevail if all the decay products in each series were in equilibrium with the parent radon. However, it is simpler to evaluate this factor in terms on an equilibrium equivalent radon concentration, EEC. This quantity, EEC, represents the activity concentration of the radon gas that would have to exist in complete equilibrium with the decay products if the short-lived decay products had the same PAEC as in the nonequilibrium mixture. The units of EC are Bqm . ... 

Apart from the activity ratios of the radon-222 decay product radionuclides, the residence time of tropospheric aerosols can be derived from the activity ratios of the fission product radionuclides released into the atmosphere during the explosions from nuclear weapons testing or nuclear reactor accidents, such as Sr/ Sr and " Ba/ Sr. These nuclide ratios are considered as nuclear clocks. The applicability of the radionuclide ratios depends on whether steady-state conditions hold at the time and place of measurement and on the kind of sample, whether surface air or precipitation (rain or snow), used for the radioisotope activity determination. 

Figure 5.6 shows the unattached fraction of radon (/ ,Rn) and thoron (/p,Tn) decay products as a function of the particle concentration of atmospheric aerosols. The fp values as a function of the particle concentration, Z, are measured by means of a condensation nuclei counter (CNC). Many working places have aerosol sources due to human activities and combustion and technical processes with a high particle concentration, Z > 4 X 10 particles cm , and therefore fp values below 0.01. The fp values are higher than 0.1 for places with particle concentrations <4 x 10 particles cm . This is the case in poorly ventilated rooms (ventilation rate <0.5 h ) without additional aerosol sources, rooms with an operating air cleaner and poorly ventilated underground caves. For the unattached thoron decay products in indoor air, the unattached fraction is estimated by the equation... 

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