Search PubMed⌕ Search

Biomedical subjects

N H Harley

Publications and source records attributed to N H Harley.

At least 19 recordsLinked to original sources
PubMed1991

Validation of a personal radon monitor for use in residential 22Rn exposure studies.

A personal radon monitor (PRM) has been developed and validated for use in studies of residential 222Rn exposure. A pilot study was performed in six New Jersey homes with elevated Rn concentrations. Occupants wore PRMs, and identical monitors were placed in many rooms of the home. Extensive assessment of PRM performance has been done. A simple model for personal Rn exposure has been tested and measured occupant exposures have been compared with stationary Rn measurements. The PRM works well, with precision limited by the counting error in the exposure range examined (2-100 kBq m-3 h). The PRM sensitivity is 2.2 kBq m-3 h, and its efficiency is 2.6 tracks (kBq m-3 h)-1 per 81 mm2 film.

Air Pollutants, Radioactive↗
PubMed1991

Personal and home 222Rn and gamma-ray exposure measured in 52 dwellings.

A personal 222Rn and gamma-ray detector has been developed. The detector precision is limited only by the Poisson counting error and has a lower limit of detection in this study of 4.5 kBq m-3 h (4 pCi L-1 day). The detector was used in a study of 52 homes in Illinois to measure the personal exposure vs. the simultaneous exposure on all levels of the home. The ratio of personal exposure to basement 222Rn concentration averaged 0.22, with a high degree of scatter (R2 = 31%). The ratio of personal exposure to first floor 222Rn concentration was 0.71, with good correlation (R2 = 85%). In the absence of personal monitoring data, the best estimate of personal exposure appears to be from measurements in the first-floor living space of the home.

Air Pollutants, Radioactive↗
PubMed1991

Methodology issues in risk assessment for radon.

The alpha dose per unit radon daughter exposure in mines and homes is comparable at about 5 mGy/WLM. This means that excess lung cancer risk determined in follow-up studies of miners should be valid to extrapolating to environmental populations. There are several models currently used for risk projection to estimate lung cancer in the U.S. from indoor radon exposure. The accuracy of the estimates depends upon the quality of the exposure data and the models. Recent miner epidemiology confirms that excess lung cancer risk decreases with time subsequent to cessation of exposure. The most rigorous ecological study, to date, shows a persistent negative relationship between average measured indoor radon in U.S. counties and lung cancer mortality. A model for lung cancer risk is proposed that includes smoking, urbanization, and radon exposure. The model helps to explain the difficulties in observing the direct effects of indoor radon in the environment.

Dose-Response Relationship, Radiation↗
PubMed1991

An improved 222Rn canister using a two-stage charcoal system.

A prototype for an improved passive 222Rn canister (R-Canister) was designed and compared to conventional charcoal canisters for its adsorptive and desorptive characteristics following exposures to 222Rn at 23 degrees C in the presence of water vapor. The R-Canister, containing a two-stage charcoal system, minimizes the adverse effects of water vapor by maintaining the amount of adsorbed water vapor in the primary Rn adsorbent below the "break-point" of the charcoal. This is achieved by the placement of a desiccant charcoal cartridge 6 cm above the primary Rn adsorbent. The optimal bed depth of the primary adsorbent, determined from a diffusion study, was found to be 2.3 cm. The measured value for the effective diffusion coefficient of RN in a peat-based charcoal at 15% humidity and 25 degrees C is 7.97 x 10(-10) m2 s-1. Exposures to 70% humidity for 7 d increased the buildup time-constant of Rn in the R-Canisters by 33% as compared to R-Canisters exposed to 15% humidity. At relative humidities ranging from 15-70%, the 222Rn buildup time-constant of the R-Canister ranged from 43-94 h, whereas the desorption time-constant ranged from 46-64 h. Typical buildup time-constants and desorption time-constants for conventional fully-opened charcoal canisters currently in field use ranged from 30-43 h and 17-29 h, respectively, over the same range of humidities.

Air Pollutants, Radioactive↗
PubMed1990

Adsorption and desorption of noble gases on activated charcoal: I. 133Xe studies in a monolayer and packed bed.

Detailed desorption studies using petroleum-based activated charcoals were conducted in monolayers and packed beds. Less extensive studies were conducted on several other types of charcoal. Kinetic studies, using 133Xe, demonstrated the existence of a micropore volume with entrance capillaries that together determined the response characteristics of charcoal to external concentration gradients of tracer gases. This new two-phase model, composed of micropores and entrance capillaries, describes the desorption dynamics of an adsorbed gas in the presence of water vapor. Condensed water vapor in the entrance capillaries of the charcoal reduced the effective pore radius and increased the diffusion half-time. Water could also adversely affect the integrating capability of the charcoal dramatically if the adsorbed water completely blocked the entrance capillaries. The amount of adsorbed water required to block the capillaries varied with the charcoal type and was termed here as the "break-point." The desorption parameters measured in this work can be used to design an improved passive Rn monitor to effectively integrate during a 3-7 d exposure period by eliminating the adverse effects of water vapor. The improved canister design would provide more accurate and reproducible measurements of indoor Rn concentrations than are currently available.

Adsorption↗
PubMed1990

Adsorption and desorption of noble gases on activated charcoal: II. 222Rn studies in a monolayer and packed bed.

The adsorptive and desorptive characteristics of canisters containing a petroleum-based charcoal were investigated under controlled conditions of temperature, relative humidity, and Rn concentration. Charcoals exposed in a monolayer and packed bed during exposure intervals of 1-7 d demonstrate that Rn adsorption and desorption are dependent on bed depth and the amount of water adsorbed. Changes in the adsorptive and desorptive properties of the charcoal occurred near the break-point where the pores became occluded by water vapor that condenses in the entrance capillaries. Radon-222 adsorption is decreased by an order of magnitude as the amount of adsorbed water exceeds the break-point of the charcoal. The reduction in pore surface due to adsorbed water results in a marked increase in the rate of Rn loss from exposed canisters, accounting for reduced adsorption. The apparent desorption time-constant for a 2-cm bed of loose Witco 6 x 10 mesh charcoal containing 0.220-0.365 kg H2O kg-1 is typically between 2-8 h. The apparent desorption time-constant for an equivalent packed bed containing a water vapor content of 0.026-0.060 kg H2O kg-1, which is below the break-point of the charcoal, is about 15-30 h. Conventional charcoal canisters, if exposed in the fully-opened configuration, can achieve the break-point in less than 4 d at 70% humidity. The use of a diffusion barrier would allow for longer exposure times until the break-point of the charcoal is achieved.

Adsorption↗
PubMed1990

Measured intake and excretion patterns of naturally occurring 234U, 238U, and calcium in humans.

The normal dietary and fluid intake and urinary and fecal excretion of 234U and 238U were determined in humans under strictly controlled conditions in the Metabolic Research Ward at Hines Hospital. These values formed the basis of the metabolic balances of these uranium isotopes. The major pathway of 234U and of 238U excretion was via the intestine while the urinary 234U and 238U were very low, averaging 2% of the total excretion. The uranium balances were roughly in equilibrium. These data were used in combination with measurements of tissue concentrations of uranium from nonoccupationally exposed humans to calculate steady-state uptake factors for environmental exposure to uranium isotopes during baseline conditions of a normal dietary intake.

Animals↗
PubMed1989

Determining the charged fractions of 218Po and 214Pb using an environmental gamma-ray and Rn detector.

The rate of 218Po and 214Pb atoms collected electrostatically inside an environmental gamma-ray and 222Rn detector (EGARD) was measured. These measurements were used to directly infer the charged fraction of 218Po and to calculate the charged fraction of 214Pb. Thirty-two percent of the 218Po was collected electrostatically using approximately -1500 V on a 2.54 cm diameter Mylar covered disc inside a vented A1 EGARD of 1 L volume. About 91% of the 214Pb is collected electrostatically under the same conditions. The measurements were performed in a calibrated 222Rn test chamber at the Environmental Measurements Laboratory (EML) using the Thomas alpha-counting method with 222Rn concentrations averaging about 4300 Bq m-3. The atomic collection rates were used with other measured quantities to calculate the thermoluminescent dosimeter (TLD) signal acquired from EGARD for exposure to 1 Bq m-3 of 222Rn. The calculations account for 222Rn progeny collection using a Teflon electret and alpha and beta detection using TLDs inside EGARD. The measured quantities include the energies of 218Po and 214Po alpha-particles degraded by passage through the 25 microns thick electret. The TLD responses to these alpha- and beta-particles with an average energy approaching that obtained from the combined spectra of 214Pb and 214Bi were also measured. The calculated calibration factor is within 30% of the value obtained by exposing EGARD to a known concentration of 222Rn. This result supports our charged fraction estimates for 218Po and 214Pb.

Air Pollutants↗
PubMed1989

Radon: is it a problem?

Radon gas is a major source of radiation exposure to the general public. Radon-222 is a product of uranium-238, present in varying concentrations in all soils. Radon enters buildings from soil, water, natural gas, and building materials. Its short-lived breakdown products, termed "radon daughters," include alpha-emitting solids that can deposit in the lungs. Firm evidence links lung cancer risk in miners with high exposure to radon daughters. The amount of risk associated with the much lower but chronic doses received in buildings is difficult to establish. By some extrapolations, radon daughters may be responsible for a significant number of lung cancer deaths. The existence or extent of synergism with smoking is unresolved. Local conditions can cause high levels of radon in some buildings, and measures that reduce indoor radon are of potential value.

Bismuth↗
PubMed1988

Interaction of alpha particles with bronchial cells.

The alpha-activity on the bronchial airways has been calculated for 222Rn daughter exposures producing observable excess bronchogenic lung cancer in underground miners. The activity distribution of aerosol particles with attached 222Rn daughters on the bronchial tree is truly diffuse because of the short half-life of the daughters and the large number of particles in the ambient aerosol. From the bronchial airway activity and the minor epidemiology, it can be shown that it requires, on average, 4 X 10(9) stem cells in bronchial epithelium to be hit in order to produce an observed lung cancer. For very high 222Rn daughter exposures of miners, multiply hit cells are highly probable; yet the lung cancer response is lower per unit exposure at high exposures than for mining exposures--near those sustained in the environment probably due to stem cell death. A knowledge of the number of multiply hit cells in miners permits some infererences to be made about the effectiveness of particulate versus diffusely distributed alpha emitters in the lung, namely, that particulates should not be significantly more effective in lung cancer induction than a diffuse distribution.

Air Pollution, Radioactive↗