S.K. Dua

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.

Estimation of the deposition of polydisperse hygroscopic aerosol particles in the respiratory tract

Abstract A method is described to estimate the total and regional deposition of polydisperse aerosol particles from data on the deposition of different salt aerosol particles described in literature (Ferron et al. , J. Aerosol Sci. 1988, 19, 611) and own calculations. This method is applied to estimate the regional deposition of a Na 2 S 2 O 5 aerosol in the human respiratory tract.

Experimental counting efficiency of the TSI aerodynamic particle sizer in the submicron size range

Abstract The counting efficiency of an Aerodynamic Particle Sizer has been determined in the size range of 0.5 to 1 μm Correction factors have been evaluated experimentally which should be used for the interpretation of the observed size distribution for sizes below 0.8 μm

Performance of a differential mobility analyzer at different gas compositions

Abstract A differential mobility analyzer (DMA) was tested at different compositions of aerosol and sheath gas flow using monodisperse polystyrene latex particles. The actual size of the particles had been determined by scanning electron microscopy. We found that different conditions of relative humidity in aerosol and sheath flow in the DMA cause changes less than 3% in particle size. Different gas compositions (air and nitrogen, air and carbon dioxide and air and helium) result in a change of particle size less than 6% if the density ratio k of aerosol and sheath flow is close to one (0.95

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.

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.

A single stage centripeter for rapid analysis of long-lived alpha emitters in air.

Rapid detection of long-lived alpha emitters such as Pu, U, T h in air is rendered difficult because of the interference of radon and thoron daughter products always present in air. It is known that radon and thoron daughter products are usually associated with the aerosols of particle size less than 0.04 pm, whereas the man-made aerosols are usually larger. This property is made use of in a specially designed single stage centripeter sampling at 1000 1./ min. This is found to have collection efficiency for long-lived isotopes around 65 % and for short-lived isotopes around 3%. As the sample comes out on a filter paper it is possible to obtain an approximate estimate of contribution from radonlthoron daughter products by counting the sample reversed, taking advantage of the alpha energy differences between radon and thoron daughter products and U, T h or Pu. Therefore, even this 3 % can be determined and discounted. Comparison is made between the present instrument and the annular impactor, an instrument also based on the principle of size separation. I t is concluded that this instrument has several desirable features compared to the annular impactor and is better suited for field use.