Size distribution daughters

The small size of daughter partieles and only very small ehanges of the parent erystal size distribution during eaeh run indieate that substantial gross partiele fragmentation does not oeeur. Partiele dispersion oeeurs mainly due to erosion of the erystal surfaee in the inert solutions. 

George, A.C., L. Hinchliffe and R. Sladowski, Size Distribution of Radon Daughter Particles in Uranium Mine Atmospheres, HASL-326, 1977. 

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). 

Simultaneous measurements of the radon daughter concentrations, the ventilation rate and the size distribution of the inactive aerosol have been performed in two bedrooms, a living room and a cellar. The measured radon daughter concentrations were fitted by the room model to optimize the deposition rate of the unattached daughters. The mean value was 18/h in the rooms and 8/h in the cellar. 

Together with the radon daughter measurements, nearly continuous measurements of the ventilation rate are performed by means of the release of N2O tracer gas and observation of its decay with an infrared spectrometer (Miran 101). Furthermore the aerosol concentration and size distribution are monitored every 20 to 30 min with an automated aerosol spectrometer (Raes et al.,1984). 

The environmental conditions for each of the cases considered below are summarized in Table III all these parameters are constant in time. The build up of the nucleation mode of the stable particles and the build up of both the nucleation and accumulation modes of the radon decay products is calculated, and the results are given after a process time of one hour. Figures 1 to 5 show the size distributions of stable and radioactive particles, and Table IV gives the disequilibrium, the equilibrium factor F, the "unattached fraction" f and the plate-out rates for the different daughters. 

Approaching from another direction, Sinclair et al (1978) and Knutson et al (1984) report that diffusion battery measurements of radon daughter aerosol-size distributions often show a small peak which could be interpreted as the unattached fraction. Its position would indicate diffusion coefficients from 0.0005 to 0.05 cm /sec. 

In 1975 there was a new development in the use of wire screens Sinclair and Hoopes (1975) described a diffusion battery (for measuring the particle size of aerosols) made of very fine 635-mesh stainless steel screen. An empirical equation was developed for the collection efficiency. This diffusion battery has become one of the standard techniques in aerosol measurements. Later, Sinclair et al (1978) described a screen diffusion battery configuration suited for measuring the activity - weighted size distribution of radon daughter aerosols. 

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. 

Table II. Summary of Mean Monthly Activity Median Aerodynamic Diameters (AMAD) and Geometric Standard Deviations (tfg) of Radon and Thoron Daughter Size Distributions in Ambient Aerosols...

George, A.C., Hinchliffe, L. Sladowski, R. (1975) Size distribution of radon daughter products in uranium mine atmospheres. American Industrial Hygiene Journal, 34, 484-90. 

The birth fimction for conservation of volume must be consistent with the death function because each particle death results in the birth of smaller particles, resulting from commimition. When particles of size L break, they produce a suite of daughter particles, called the primary progeny, with a size distribution p(x, L). This function applies... 

The characteristics of aerosols carrying natural and artificial radionuclides are generally quite different. The size distribution of radon daughters is bi-modal. The median diameter of free atoms is about 10 pm, while that of attached radon daughters... 

The experimental data of Risso and Fabre [99] also indicate that an equal size daughter distribution is more common for bubble breakage than an unequal one. Contrary, Hesketh et al [33, 34] investigated bubble breakage in turbulent flows in horizontal pipes and concluded that an unequal size daughter distribution is more probable than an equal size one. The daughter bubble size distribution model of Luo and Svendsen [74] rely on the assumption that unequal sized is more probable than equal size breakage in accordance with... 

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