Activity size distribution measurements

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... 

Three different experimental protocols were used throughout the work. Two protocols were used to determine the activity size distribution, the first protocol, based on individual progeny, for the bulk of the measurement days (Jan 29 to Feb 6) and the second, based on Working Level, for the last two days (Feb 7 and 8). The third experimental protocol was used for general determination of Working Levels from Jan 29 to Feb 6. 

The activity size distributions were determined from the calculated penetration values in the diffusion batteries using the method outlined for aerosol size measurement (equation (6) for RnWL and equations (8) and (9) for 222Pb concentration). 

Pb-212 activity size distribution data had to be rejected due to a pump failure during measurements. 

Reineking, A. and J. Porstendorfer, High-volume Screen Diffusion Batteries and the Alpha Spectroscopy for Measurements of the Radon Daughter Activity Size Distributions in the Environment, J. of Aerosol Science 17 (1986) (accepted for publication). 

In order to examine the process of ultrafine particle formation, a joint series of experiments were conducted at the Denver Research Center of the U.S. Bureau of Mines. In the Denver radon chamber, the activity size distribution of the ultrafine mode was measured using the mobility analyzer designed by Chu and Hopke (1985), the separate single screen method (Holub and Knutson, 1987), and the stacked single screen method (Holub and Knutson, 1987) for various relative humidities and for various concentrations of SO. The results... 

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

The experimental materials and procedures are described in detail by Kaiser et al. (7), including the characterization of the activated caibon fabrics used such as BET aurface area and pore size distribution measurements by well established methods (2, 5), the composition of the carrier of the adsorption solution, and of the adsorption test procedure.. The key difference is the use of of a 70 ppm solution of chemical agent Bis (2-chloroethyl) sulfide (HD) in HFE-7100 as a challenge solution instead of a 70 ppm solution of CEES in HFE-7100. The HD was obtained from the US Army Edgewood Chemical and Biological Center s... 

Yenkie, M.K.N., and Natarajan, G.S., Determination of specific surlace area of granular activated carbon by aqueous phase adsorption of phenol and from pore size distribution measurements, Sep. Sci. Technol., 28(5), 1177-1190(1993). 

A histogram of the activity size distribution of Be versus aerodynamic diameter Dp) is presented in Figure 2.1. This distribution was selected by Papastefanou and loannidou (1995) from 11 atmospheric aerosol sampling measurements made over an almost 2-year period at Thessaloniki, Greece (40°38 N, 22 58 E) by using Andersen 1 ACFM cascade impactors at a flow rate of 1.7 m h (28.31 min or 1 ft min ). 

Beryllium-7 aerosol measurements carried out by Papastefanou and loannidou (1995) at sea level in a coastal area, in a hilly area, at 250 m height and on the top of a mountain, at 1000 m altitude, showed that the Be activity size distribution dominated a smaller size range of aerosol particles with an AMAD of 0.68 pm (ag = 2.18) at a height of 250 m and an AMAD of 0.68 pm (ag = 2.24) at a height of 1000 m, showing a dependency on altitude. In marine environments at sea-level, the " Be activity size distribution dominated a higher size range of aerosol particles with an AMAD of 0.82 pm (ag = 1.88). 

The activity size distributions of Pb and Pb versus aerodynamic diameter (Dp) are represented by four subplots (Figure 2.5). These distributions were selected from 46 measurements made over a 10-month period at Oak Ridge, Tennessee (35°58 N, 84°17 W) by... 

Mean observed Pb and Pb activity size distributions and frequency of dominance (44 measurements)... 

Table 2.4 summarises the activity median aerodynamic diameter (AMAD) of Pb and Be and the mass median aerodynamic diameter (MMAD) of SO found in measurements made in the spring period. Beryllium-7 activity size distributions are substantially smaller than 804 , regardless of the time of year. The Pb data included in Table 2.4, while limited, suggest that summer aerosol particle sizes are larger than winter aerosol particle sizes. 

In contrast to the findings of Bondietti and Brantley (1986), lost et al. (1986) found no increase of the activity median aerodynamic diameter, AMAD, during the measurement period. They believed that this increase might not reflect the original release at Chernobyl, but was due to transport effects. Apart from this, the activity size distribution of Cs from the Chernobyl fallout was very similar to the activity size distribution in the fallout from nuclear weapons tests (Lockhart et al., 1965b), in contrast to the activity size distribution found in the stratosphere, which is shifted towards smaller particles (Persson and Sisefsky, 1971). 

Robig, G., Becker, K.H., Hessin, A., Porstendorfer, J., Scheibel, H.G. (1980). A cascade impactor caUbration for measurement of activity size distributions in the atmosphere. In Proceedings of 8th Conference in Aerosol Science. Georg-August-University, Gottingen, Germany, pp. 96-102. 

In the estimation of the dose conversion factor, DCF, by dose model calculations, the activity size distribution in terms of potential alpha energy concentration (PAEC) is an important input parameter. For practical reasons related to measurements, the activity size distribution should be divided into three parts as follows ... 

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. 

There are two methods that can be used to make activity-weighted size distribution measurements screen diffusion batteries (Hopke et al., 1992 Cheng et al., 1994) and all-type cascade impactors. Although screen diffusion batteries have been widely used, the activity size distribution cannot be easily obtained with them due to technical and calculation complexities. Even when conventional equipment and the impactor method are used it is difficult to obtain a result that is not affected by the decay of the radioisotopes. 

---