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Biomedical subjects

P Kotrappa

Publications and source records attributed to P Kotrappa.

At least 19 recordsLinked to original sources
PubMed1995

Electret method for continuous measurement of the concentration of radon in water.

A passive system using an electret ion chamber to measure dissolved radon in a water sample has been recently described. In the current work, an electret ion chamber has been used to measure time-averaged concentration of dissolved radon in water. A steady concentration of radon in water is generated by bubbling radon gas into water in a 20-L jar and maintaining constant rates of feed and bleed of the water. To perform the measurement, the outgoing water flows into a 4-L cylindrical chamber. Air is bubbled at 1 L min-1 through a 10 cm long sintered stainless steel tube immersed in this water releasing the radon from water into the chamber volume. A 1-L electret ion chamber ("H" chamber) loaded with an electret is hung in the 4-L chamber. Radon diffuses into the "H" chamber through its tyvek (carbon-coated) covered openings. The radon concentration in air is measured from the change in electret voltage. The concentration of radon in water is then obtained from the concentration of radon in air and the air and water flow rates. For comparison, the radon concentration in water was measured using a standard liquid scintillation counting method. For the concentration range covered (4.7 to 72 Bq L-1), there was a good agreement between the two methods.

Radon↗
PubMed1992

Elevation correction factors for E-PERM radon monitors.

E-PERM radon monitors are based on the principle of electret ion chambers and are usually calibrated in a standard radon chamber located at sea level. Corrections are needed if the monitors are used at elevations other than sea level. These were experimentally determined for three models of commercially available electret ion chambers (E-PERM) as functions of elevation above sea level. These corrections are minor and should be applied for obtaining more accurate results.

Calibration↗
PubMed1990

A practical E-PERM (electret passive environmental radon monitor) system for indoor 222Rn measurement.

The technical and scientific basis for the measurement of indoor 222Rn concentration using an E-PERM (Electret passive environmental radon monitor) has been described in our earlier work. The purpose of this paper is to describe further development of a practical and convenient system that can be used routinely for indoor 222Rn measurement. The ion chamber is now made of electrically conducting plastic to minimize the response from natural gamma radiation. A spring-loaded shutter method is used to cover and uncover the electret from outside the chamber. The electret voltage reader has been modified to improve the accuracy and the ease in operation. The calibration, performance, error analysis, and lower limits of detection for these standardized versions of E-PERMs are also described.

Air Pollutants↗
PubMed1988

An electret passive environmental 222Rn monitor based on ionization measurement.

The electret passive environmental 222Rn monitor (E-PERM) is an extension of electret dosimeters used for measurement of x and gamma radiation. An E-PERM consists of a small cup or canister, having an electret at the bottom, and a filtered inlet at the top. The 222Rn gas entering through the filter and the decay products formed inside the cup generate ions which are collected by the electret. The reduction of charge (or surface potential) on the electret is a measure of time integrated 222Rn exposure. An E-PERM of 220-mL volume with an electret of 0.23 cm thickness gave a surface potential drop of 2.5 V for 37 Bq m-3 d (1 pCi L-1 d). The electret voltage was measured with a specially built surface potential voltmeter. This sensitivity was found adequate for a 1-wk measurement of 222Rn in homes. For longer term measurements, an E-PERM of 40-mL volume and an electret of 51-micron thickness was developed which gave a surface potential drop of 2.6 V for 37 Bq m-3 y (1 pCi L-1 y). Other combinations of chamber volume and electret thicknesses gave responses between these two values. The surface potential of electrets made from Teflon FEP were shown to stay stable even under extreme conditions of relative humidity. The ion collection process in E-PERMs was also shown to be independent of humidity down to an electret surface potential of 100 V.

Environmental Monitoring↗
PubMed1986

Radium-226 body burden in U miners by measurement of Rn in exhaled breath.

Uranium miners were made to inhale Rn-free medical O2 and exhale through a 5.2-1 A1 chamber before reporting to work. The chamber was sealed and isolated from the sampling circuit. An electrostatic plate collected the freshly formed Rn-decay products. The subsequent programmed alpha counting of the plate yielded a Rn concentration in the exhaled breath. Assuming that the exhaled breath represents a certain fraction of the Rn produced inside the body, the body burden of 226Ra was calculated. Standardisation of this procedure and the data collected on 310 miners are discussed. The procedure is simple and applicable for routine measurements. The miner needs to be in the laboratory for only 10 min. The system is also portable for field application. For routine use, the minimum detectable concentration is 3.87 Bq X m-3 which corresponds to a body burden of 0.26 kBq in a typical miner, if one assumes the Rn release fraction from the body as 84%. The system offers a more convenient and sensitive alternative to whole-body counting of workers for 226Ra.

Body Burden↗
PubMed1986

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.

Body Burden↗
PubMed1982

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.

Radiation Monitoring↗
PubMed1977

Scintiphotography of lungs with dry aerosol--generation and delivery system: concise communication.

A compressed-air nebulizer with low holdup and high output was used to nebulize [99mTc] pertechnetate presented in normal saline. Generated droplets were dried in line and led to an inhalation chamber from which the dry aerosol was inhaled using a nose or mouth inhalation unit. The mass median diameter of the particles was 0.8 microns, with an associated geometric standard deviation of 2.0. The deep lung delivery efficiency--defined as the ratio of the activity deposited in the lung area to the activity nebulized--was found to be reproducible and consistent (15-22%) in all the subjects studied. A 3-5 min inhalation of aerosol, nebulized from 20 mCi, was sufficient to provide a lung image of good information density. No noticeable deposit was seen in the trachea or major brochi. The system is inexpensive, stable in performance, adaptable to other solutions or colloids, and is promising for routine use.

Aerosols↗