P. Kotrappa

Electret--a new tool for measuring concentrations of radon and thoron in air.

AbstractElectret is an electrical analogue of a permanent magnet and it carries permanent electrical charge. A negatively charged teflon electret is used for the collection of decay products of radon or thoron (positively charged) formed inside a 10-l. wire mesh chamber whose sides are covered with

Passive measurement of radon and thoron using TLD or SSNTD on electrets.

An electret is an electrical analogue of a permanent magnet and it carries a permanent electric charge. Our previous work has shown that such electrets are suitable for collecting decay products of radon and thoron in passive chambers. In the present work, the decay products are directly collected on the surface of a TLD or SSNTD providing in situ registration of the radiation from the decay products of radon and thoron. A 101. chamber, the sides of which were covered with a layer of Whatman No. 1 (W-1) filter paper, showed the following responses: (i) SSNTD (CR-39) recorded 92 +/- 13 tracks per cm2 per pCi/l, hr for radon and 9 +/- 1.5 tracks per cm2 per pCi/l. hr for thoron; (ii) for similar levels TLD (CaF2(Dy)) chips recorded an equivalent of 1.35 +/- 0.16 mR for radon and 0.30 +/- jk0.09 mR for thoron. Taking advantage of the differential response of the two chambers (one covered with a layer of W-1 filter paper and the other with a 75 mm polyurethene foam), simultaneous measurement of radon and thoron could be achieved.

Equilibrium charge distribution on doublets and triplets of uniform 0.500 μ diameter polystyrene spheres—an experimental study

Abstract Experimental study of the equilibrium charge distribution of the doublets and triplets of 0.500 μm dia. polystyrene latex spheres was carried out using a parallel plate mobility spectrometer. It was observed that the fraction of doublets carrying two charges was 9% more than those carrying unit charge. This is not in accordance with the prediction of Boltzmann law. The fraction of triplets carrying two and more charges was also more than that expected from Boltzmann distribution for spheres of equivalent volume diameter. The observed charge distribution of doublets and triplets was symmetrical with respect to the sign of charge.

Green's function method for aerosol penetration in channels under laminar flow conditions

A generalized method based on Greens function technique is developed to calculate the penetration fraction of particles by diffusion, formed from a given source in a gas under laminar flow, in cylindrical and rectangular channels. Both the initial value and the formation-in-flight types of problems are brought together in one formal procedure. The task of having to solve the convective-diffusion equation, for a given distribution of source density in the case of formation-in-flight problems, is altogether eliminated. The effect of a first-order reaction, like radioactive decay, is taken into account. Linear approximation for the shift in the eigenvalues due to the reaction term is given for small values of the dimensionless reaction rate constant. Finally, the solution available for an exponentially decreasing source in a cylindrical channel is found to be incorrect and the correct expression is derived using this method.

Preparation of monodisperse tagged polystyrene aerosol using an aerosol centrifuge

Abstract A method of preparing and aerosolizing monodisperse particles of polystyrene tagged with 51 Cr is discussed. The procedure consisted of four steps: generating polydisperse polystyrene aerosol by nebulizing polystyrene solution in xylene containing 51 Cr in the form of chromium acetyl acetonate, separating and collecting this polydisperse aerosol in monodisperse size groups on a polythene collection foil of Lovelace Aerosol Particle Separator (LAPS), resuspending the monodisperse particles in water and the subsequent aerosolization. Because of the presence of xylene vapour in the aerosol stream, a new sampling procedure was needed for the second step. The stream air needed for the LAPS was taken from the aerosol chamber itself through a series of filters in order to match the vapour concentrations between the stream air and aerosol air, an essential step to achieve separation in the LAPS. It was possible to obtain tagged aerosols in the size range of 0.7 μm to 5 μm with a standard deviation of less than 10 per cent.

Measurement of 220Rn in exhaled breath of Th plant workers.

The concentration of 220Rn in the exhaled breath of workers currently employed in a Th plant was measured using a double filter system. The results are expressed in terms of the equivalent activity of 224Ra freely emanating 220Rn at the mouth. Measurements performed on 176 subjects, without isolating them from day-to-day work, showed 220Rn levels having a median of 0.74 Bq, with the group consisting of sweepers and helpers showing the highest average level (1.68 Bq). Measurements performed on 15 selected workers, after isolating them from work for a minimum duration of 48 h yielded 220Rn levels which were consistently lower than those obtained in the first measurements. This is attributed to the material undergoing short term elimination from the body. It was also found from the latter measurements that the group consisting of workers engaged in radioactive work for more than 24 y has an average 220Rn level of 2.65 Bq which is significantly higher than that (1.27 Bq) found in the group that has worked for less than 12 y. A conversion factor of 0.09 deduced by earlier investigators is assumed to be valid for estimating the actual 224Ra burdens from the 220Rn data.

Diffusion of radon gas and its progeny in a narrow slit parallel plate mobility spectrometer

Abstract The concentration distribution of a gas, radioactive or otherwise, injected into a parallel plate mobility spectrometer from a central narrow slit is theoretically investigated both for large and small axial parameters. It is found that for a parabolic velocity profile, the mean concentration of the gas at any lateral cross-section increases along the direction of flow to a saturation value which is 1.5 times the mean concentration at the inlet. For slug flow, on the other hand, the mean concentration remains constant throughout. The possible applications of these results in the further characterization of the instrument are suggested. Finally the solutions are applied to calculate the penetration of the neutral fraction of disintegration products of radon and thoron in the spectrometer.

The performance of aerosol centrifuges at unmatched relative humidities between stream and aerosol air

Abstract Calibration of Lovelace Aerosol Particle Separator, a Stober type of aerosol centrifuge, was observed to shift when the relative humidities of aerosol stream and stream air were not matched. Systematic investigations were made to study the effect using Dow monodispersed polystyrene latex particles of 0.797, 1.091 and 2.020 μm sizes. Relative humidities (r.h.) were varied in the range of 22% to 80%. When aerosol air was dry (r.h. 22%) and stream air was humid (r.h. 80%), particles deposited farther than the positions corresponding to the matched conditions and the reverse was observed when the aerosol air was humid and the stream air dry. Resolutions were poorer for the unmatched conditions. Results are discussed.

Dynamic shape factors for PuO2 aerosols useful in autoradiographic particle size analysis.

Dynamic shape factor ( K ) of an irregularly shaped particle is related to its aerodynamic diameter (Due) by the following equation:

A study of the attachment of thoron decay products to aerosols using an aerosol centrifuge

Abstract An aerosol centrifuge is used for the study of the attachment of thoron decay products to aerosol particles under dynamic flow conditions. The number concentration of aerosols was kept high (105–106 particles cm−3) as compared to the number of decay product atoms (102–103 cm−3) as is usually the case in a mine atmosphere. The polydispersed aerosols flow in and out of a chamber containing a steady source of thoron and the aerosols tagged with the decay products were separated into different size groups by an aerosol centrifuge (Lovelace Aerosol Particle Separator). The average activity per particle was fitted as a power function of the radius in the form of AP = αRb. The average value of b was found to be 1.08 ± 0.054 for particles in the radii range 0.25–1.35 μm and 1.34 ± 0.12 for particles in the radii range 0.1–0.33 μm.