Activity size distribution

However, these results may need to be modified by the findings of Porstendorfer et al. (1987), Vanmarcke et al. (1987), and Knutson et al. (1985) that the "unattached" Po-218 containing molecules are actually part of an ultrafine mode (0.7 - 2.0 nm) in the activity size distribution. Thus, they are not free molecules and will move with a reduced diffusion coefficient based on the size of these ultrafine particles. 

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). 

On the last two days, Working Levels determined by equations (6) and (7) for activity size distribution were used. 

Mine Date Activity size distributions, AMD ( um) Aerosol size distribution ... 

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

Figure 5. Activity size distributions for 218Po (trackless mine).

The activity size distribution of the radon daughter aerosols. 

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). 

Figure 4a. Evolution of the active size distribution on the same days as in Figure 3.

The determination of the activity size distribution of the ultrafine ions is of particular interest due to their influence on the movement and deposition of Po-218. These ultrafine ions are the result of radiolysis and their rate of formation is a function of radon concentration, the energy associated with the recoil path of Po-218, and the presence of H O vapor and trace gases such as S02 a joint series of experiments utilizing a mobility analyzer, the separate single screen method, and the stacked screen method were conducted to examine the activity size distribution of the ultrafine mode. 

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... 

Figure 3 also represents the affect of SC>2 and H20 on particle formation. High concentrations of SC>2 (10-20 ppm) in the presence of H20 result in a decrease in the total number of ions but an increase in the number of ions with lower mobilities. This is especially significant for Po-218 ions with mobilities centered around 2.0 cnrV s . At low humidity and high S02 concentrations there is an increase in particle formation at higher mobilities. Under this set of conditions the examination of the activity size distribution of the finest mode of the ultrafine ions is possible. 

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. 

There is very recent evidence that there is an extremely fine mode in the particle activity size distribution. Reineking, Becker and Porstendorfer (1985) used several diffusion batteries to determine a Po-218 activity peak in the 1-3 nm diameter range. 

Cheng, Y. S. Yu, C. P. "Hi, K. W. Intercon parison of Activity Size Distributions of Thoron Progeny by Alpha and Gamma Counting Mediods. Health Phys. 1994,66,72-79. 

Depending on their source there may be from one to three distinct maxima in the surface and volume or mass distributions. The activity size distribution of a radionuclide-associated aerosol particle is a surface distribution (Papastefanou and Bondietti, 1987). 

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). 

Fig. 2.1. (a) Aerodynamic size distribution of Be ambient aerosols, (b) Relative activity size distribution of Be in outdoor air. 

Rdbig et al. (1980) reported that the distribution of the long-lived radionuclide Be was shifted to large particle sizes due to long residence times of Be in the atmosphere. An equivalent aerodynamic diameter of about 0.65 pm for Be might have resulted from the plot of the activity size distribution of the ambient air obtained by a high volume cascade impactor... 

Activity size distributions of the radon product decay aerosols 3.4.1. Lead-214 and aerosol size distributions... 

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