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At least 1,243 records · Page 69Linked to original sources
PubMed1983

Airborne radionuclides and radiation in buildings: a review.

This paper reviews the literature on sources and measurement of natural airborne radionuclides and radiation in buildings. It also briefly reviews control measures and suggests areas for further research. The major emphasis is given to 222Rn and its daughters, since they typically cause the largest organ dose to the general population, most of which arises from indoor exposures. The indoor radiation field from radionuclides fixed in building materials and soil is also given substantial treatment.

Air↗
PubMed1983

Radiation exposure of the respiratory tract and associated carcinogenic risk due to inhaled radon daughters.

The atmospheric content of radon and its decay products contributes significantly to the radiation exposure of man even in the normal environment. In this study, the risk for lung cancer induction associated with normal exposure to natural radionuclides is assessed in Salzburg, Austria. Altogether more than a thousand rooms have been investigated by using combined radon grab-sampling methods together with continuous measurements of radon and daughters at different control stations. Dose calculations were carried out for 729 demoscopically selected test persons, considering individual differences in age, sex and life-style and atmospheric nuclide concentrations at different sites. Using a specially developed age-dependent lung model, the dose frequency distribution of the absorbed dose to the basal cells of the bronchial epithelium could be evaluated for the population of Salzburg. Dose modifications caused by anatomical and physiological variabilities as well as microdosimetric considerations of the stochastic events during energy deposition result in a significantly increased dispersion of the dose histogram. Induction of lung cancer due to inhalation of radon and decay products can be correlated with cumulative exposure based on experience with lung cancer incidence amongst uranium miners. Using the recommended range of lifetime risk values of 20-45 X 10(-5)/WLM (UN77), it is shown for Salzburg that about 15% of the observed number of lung cancer cases may be induced by natural radionuclides.

Austria↗
PubMed1983

Indoor radon progeny exposure in the Florida phosphate mining region: a review.

This paper reviews the data generated in studies of land radioactivity and indoor airborne radon progeny associated with mined and reclaimed phosphate lands in Florida. Highest indoor radon progeny levels are associated with the slab-on-grade type of construction. Concentrations exceeding 0.03 WL are associated with overburden soils, deposits and fill, while concentrations up to about 0.03 WL are associated with tailings. The lower limit for distinguishing increases above non-enhanced natural concentrations is on the order of 0.01-0.02 WL. Results of this study show that about 25% of the land produced by present methods of mining and reclamation practices would require restrictions on the type of construction or would require special construction methods. It is projected that with modification of mining and tailings disposal practices, virtually all of the land produced by mining and reclamation would be satisfactory for unrestricted construction use.

Background Radiation↗
PubMed1983

Indoor radon measurements in New Jersey, New York and Pennsylvania.

The distribution of 222Rn concentrations in 33 buildings near Canonsburg, PA, Lewiston, NY and Middlesex, NJ was investigated over a 2-yr period. One or 2 week-long time-integrated measurements of radon concentration, repeated several times during the study period, were obtained in the living and working areas of the buildings. Average air concentrations of radon, measured over the study period, varied from 0.32 to 4.5 pCi/l. among the buildings, but in only one building did the annual radon concentration exceed the U.S. Nuclear Regulatory Commission's limit of 3pCi/l. for continuous exposure in uncontrolled areas.

Air↗
PubMed1983

Radon concentrations and infiltration rates measured in conventional and energy-efficient houses.

To elucidate any connection between high radon concentrations and low-infiltration houses, we have concurrently measured the 222Rn concentration and the infiltration rate in U.S. houses. Three housing surveys have been undertaken: one in "energy-efficient" houses located throughout the U.S. and two in "conventional" houses in the San Francisco area and in Maryland. In each of the groups surveyed, no clear correlation was observed between 222Rn concentrations and infiltration rate, although each parameter varied over a wide range. Infiltration rates for the entire sample, numbering 98 houses, ranged between 0.02 and 1.6 air changes per hr, and 222Rn concentrations ranged from 0.1 to 27 pCi/l. It appears that the major cause of the observed differences in 222Rn concentration is variation from one house to another in the rate at which 222Rn enters houses from its sources.

Air↗
PubMed1983

Indoor radon levels in the northeastern U.S.: effects of energy-efficiency in homes.

The expectation of elevated 222Rn levels in modern homes that have low air interchange rates with the out-of-doors caused us to survey both solar and conventional homes in northeastern New York State. The solar homes as a group have three times the 222Rn levels of the conventional homes, and specific problems exist that are introduced or exaggerated by modern construction. For example the highest two levels of radon in the solar homes give radiation doses over 30 yr that are known to produce lung cancer in 1% of uranium miners. Summer readings in more than half of the cases are different from winter ones by a factor of two or more, so that year-round measurements are necessary for precise dosimetry. The track etching technique is ideally suited for such measurements.

Climate↗
PubMed1983

Radon and radon daughter measurements in solar buildings.

Measurements of radon and radon daughters in 11 buildings in five states, using active or passive solar heating, showed no significant excess in concentrations over the levels measured in buildings with conventional heating systems. Radon levels in two buildings using rock storage in their active solar systems exceeded the U.S. Nuclear Regulatory Commission's limit of 3 pCi/l. for continuous exposure in uncontrolled areas. In the remainder of the buildings, radon concentrations were found to be at levels considered to be normal. It appears that the slightly elevated indoor radon concentrations result from the local geological formations and from the tightening of the buildings rather than as a result of the solar heating technology.

Climate↗
PubMed1983

Concentrations of radon and its progeny in the rooms of Polish spas.

Radon concentrations and radon-daughter exposures of workers have been determined in three Polish spas where radon is used as a therapeutic agent. A wide range of values for both parameters was observed during the late 1970s, with some exposures above the annual limit of 3.5 WLM, particularly among technical personnel at a spa using uranium ore as a source. A downward trend in these exposures in recent years reflects the effect of improved practices.

Air↗
PubMed1983

The equilibrium factor F.

Consideration of the equilibrium factor F between the concentration of the radon daughters and the concentration of radon is a part of the evaluation of the measurements of radon daughter concentrations in dwellings when applying limits. Measurements of radon, radon daughters and air exchange rates have been carried out in 225 dwellings in Sweden. The F-factors have been compared with the theoretical model described by Wicke, taking into account the wall effect. The parameters of the model are discussed. The situation of the dwelling and the habits of the occupants can be expected to have the greatest importance for the F-factors although the ventilation rate is usually the most important modifying factor. For low air exchange rates (l less than 0.30 hr-1) the probability that the F-factors were between 0.28 and 0.74 was 95% calculated according to the t-distribution. The arithmetical mean was found to be 0.51. For air exchange rates close to the average rate (0.30 less than l less than 0.60 hr-1), the F-factors were between 0.21 and 0.66 with a mean of 0.43, and for high air exchange rates (l greater than 0.60 hr-1) the F-factors were between 0.21 and 0.47 with a mean value of 0.33.

Housing↗
PubMed1983

Verifying a model of radon decay product behavior indoors.

Where it is not feasible to reduce radon levels in houses, exposure to radon decay products may still be reduced through air filtration or other air treatment techniques. A model which accurately describes the behavior of decay products indoors would be helpful to development or improvement of such air treatment techniques. We use a minor modification of a well-known model to describe the behavior and fate of radon decay products in the average indoor environment, and examine the adequacy of the model to predict the impact of a variety of air treatment techniques on indoor radon decay product levels. We find that the indoor environment is successfully described by the model and that plate-out of radon decay products on surfaces is much less than previous work has suggested. We also find that the model provides a plausible explanation of the effectiveness of a variety of techniques that remove radon decay products from the air.

Climate↗
PubMed1983

The effect of electric fields on 222Rn daughter products in indoor air.

A fraction of the short-lived airborne daughter products of 222Rn are charged (positively) and can thus be removed from the air by means of an electric field. A theory is presented which gives the relation between the charged fraction and the total individual daughter activity at equilibrium as a function of the field applied. The theory also allows a deduction of the mobilities of the charged daughter products. Preliminary measurements were performed in a basement room with very low ventilation rate and fairly high radon concentration (5-10 pCi/l.). The electric field was established by applying a voltage to a wire mounted at a height of 1.7 m above the floor and 1 m from the walls. The radon concentration of the air as well as the concentration of the individual 222Rn daughter products were measured at various wire voltages. As an approximation the field was assumed to have a cylindrical configuration. The preliminary results indicate that, at moderate radon activities (lower than approx. 10 pCi/l.) and low condensation nucleus concentrations, the relative activities of the positively charged daughter products are about 1:4:0.8 at equilibrium in the absence of an electric field. The measurements also show that the Working Level may be lowered by a factor of 2-3 applying a voltage of a few thousands volts to the wire.

Air↗
PubMed1983

Automated system for measuring air-exchange rate and radon concentration in houses.

We have developed an automated system for continuously measuring the air-exchange rate and 222Rn (radon) concentration in an occupied residence. The air-exchange rate is measured over 90-min intervals by tracer gas decay using sulfur hexafluoride as the tracer gas. The radon concentration is measured over 3-hr intervals using a flow-through scintillation cell. Temperatures at up to seven points are measured every half hour. A microcomputer system controls the measurements, performs preliminary data analysis, and logs the data and the results. Continuous measurement of ventilation rate and radon concentration permits the effective radon source magnitude to be calculated as a function of time. The first field application of this system was a study in Rochester, NY, of residential air-exchange rates and indoor air quality. For the 8 houses monitored, the mean values over 4- to 14-day periods ranged from less than 0.2 to 2.2 pCi l-1 for radon, from 0.22 to 1.16 hr-1 for air-exchange rate and from less than 0.05 to 0.75 pCi l-1 hr-1 for radon source magnitude.

Electronics↗
PubMed1992

Residential radon exposure and lung cancer: an overview of ongoing studies.

This review paper summarizes the ongoing case/control studies of residential radon exposure and lung cancer. Discussion is offered in the areas of lung cancer risk factors, sample size requirements, radon exposure assessment, and meta-analysis. This is an important topic that deserves a "best effort" study design.

Case-Control Studies↗
PubMed1999

Calculation of airborne radioactivity in a Technegas lung ventilation unit.

Airborne contamination by 99Tcm has been monitored in the Nuclear Medicine Department in our hospital to assess the risk of internal contamination to occupational workers exposed to Technegas studies. An air sampler fitted with a membrane filter was used. The optimum time for air absorption for obtaining the maximum activity in the filter was calculated. Maximum activity in the membrane filter ensures minimum uncertainty, which is especially important when low-level activities are being measured. The optimum time depends on air absorption velocity, room volume and filter efficiency for isotope collection. It tends to 1/lambda (lambda = disintegration constant for 99Tcm) for large volume and low velocity. Room activity with the air pump switched on was related to filter activity, and its variation with time was studied. Free activity in air for each study was approximately 7 x 10(-4) the activity used, and the effective half-life of the isotope in the room was 13.9 min (decay and diffusion). For a typical study (630 MBq), the effective dose to staff was 0.01 microSv when in the room for 10 min.

Air Pollutants, Radioactive↗
PubMed2001

Feedback control of the rate of peat formation.

The role of peatlands in the global carbon cycle is confounded by two inconsistencies. First, peatlands have been a large reservoir for carbon sequestered in the past, but may be either net sources or net sinks at present. Second, long-term rates of peat accumulation (and hence carbon sequestration) are surprisingly steady, despite great variability in the short-term rates of peat formation. Here, we present a feedback mechanism that can explain how fine-scale and short-term variability in peat-forming processes is constrained to give steady rates of peat accumulation over longer time-scales. The feedback mechanism depends on a humpbacked relationship between the rate of peat formation and the thickness of the aerobic surface layer (the acrotelm), such that individual microforms (hummocks, lawns, hollows and pools) expand or contract vertically in response to fluctuations in the position of the water table. Hummocks (but not hollows) 'evolve' to a steady state where changes in acrotelm thickness compensate for climate-mediated variations in surface wetness. With long-term growth of a topographically confined peat deposit, the steady state gradually shifts to a thicker acrotelm (i.e. taller hummocks) and lower rates of peat formation and carbon sequestration.

Carbon↗
PubMed2001

Sexual and reproductive behaviour of Drosophila melanogaster from a microclimatically interslope differentiated population of "Evolution Canyon" (Mount Carmel, Israel).

The strong microscale interslope environmental differences in "Evolution Canyon" provide an excellent natural model for sympatric speciation. Our previous studies revealed significant slope-specific differences for a fitness complex of Drosophila. This complex involved either adaptation traits (tolerance to high temperature, different viability and longevity pattern) or behavioural differentiation, manifested in habitat choice and non-random mating. This remarkable differentiation has evolved despite a very small interslope distance (a few hundred metres only). Our hypothesis is that strong interslope microclimatic contrast caused differential selection for fitness-related traits accompanied by behavioural differentiation and reinforced by some sexual isolation, which started incipient speciation. Here we describe the results of a systematic analysis of sexual behaviour in a non-choice situation and several reproductive parameters of D. melanogaster populations from the opposite slopes of "Evolution Canyon". The evidence indicates that: (i) mate choice derives from differences in mating propensity and discrimination; (ii) females from the milder north-facing slope discriminate strongly against males of the opposite slope; (iii) both sexes of the south-facing slope display distinct reproductive and behavioural patterns with females showing increased fecundity, shorter time before remating and relatively higher receptivity, and males showing higher mating propensity. These patterns represent adaptive life strategies contributing to higher fitness.

Animals↗
PubMed2004

Forest-climate interactions in fragmented tropical landscapes.

In the tropics, habitat fragmentation alters forest-climate interactions in diverse ways. On a local scale (less than 1 km), elevated desiccation and wind disturbance near fragment margins lead to sharply increased tree mortality, thus altering canopy-gap dynamics, plant community composition, biomass dynamics and carbon storage. Fragmented forests are also highly vulnerable to edge-related fires, especially in regions with periodic droughts or strong dry seasons. At landscape to regional scales (10-1000 km), habitat fragmentation may have complex effects on forest-climate interactions, with important consequences for atmospheric circulation, water cycling and precipitation. Positive feedbacks among deforestation, regional climate change and fire could pose a serious threat for some tropical forests, but the details of such interactions are poorly understood.

Atmosphere↗