A study of indoor radon in greenhouses in Mexico City, Mexico

Enclosed spaces in contact with soil, the main source of radon, like greenhouses have potentially high radon (²²²Rn) concentrations. Greenhouses are frequented by visitors and also are workplaces. The study of radon concentrations in greenhouses is, thus, a relevant concern for public health and environmental radiation authorities. For this study, the radon concentrations in 12 greenhouses in different locations within Mexico City were measured using nuclear track methodology. The detectors used for the study consisted of the well-known closed-end cup device, with CR-39 Lantrack^® as detector material. The measurements were carried out over a period of one year, divided into four three-month sub-periods. The lowest and highest annual mean radon concentrations found in individual greenhouses were 17.0 and 45.1 Bq/m³, respectively. The annual mean averaged over all 12 greenhouses was 27.3 Bq/m³. No significant seasonal variation was observed. Using the highest annual mean radon concentration found in an individual greenhouse, and an equilibrium factor of 0.4, the effective dose from ²²²Rn and its progenies was calculated to be 339.9 nSv/h. This corresponds to an annual dose rate of 679.8 μSv/y (0.057 WLM/y) for a worker spending 4 h a day, 5 days a week, 50 weeks a year, inside the greenhouse. For a visitor spending 12 h a year inside the greenhouse the annual dose is 2.469 μSv/y. The study of indoor radon concentrations in closed buildings such as greenhouses, which are both workplaces and open to visitors, is an important public health consideration.     

Radon Mapping of Soils in St. Elizabeth, Jamaica

Soil gas measurements of radon were made in St. Elizabeth, Jamaica using nuclear track etch detectors. The results were compared to gamma-ray spectroscopy measurements made in the laboratory on soil samples collected at the radon measurement sites. An assessment of the degree of disequilibrium of uranium and thorium was also made by comparison with neutron activation analysis, delayed neutron counting and equivalent uranium and thorium measurements. The results to date for equivalent uranium and radon show a strong correlation and indicate the possibility of soil radon mapping in Jamaica using gamma-ray spectroscopy. Three anomalous sites have been identified.     

Enhanced indoor radon concentration by using radon-rich well water in a Japanese wooden house in Fukuoka, Japan

Summary Radon measurements were carried out in a Japanese wooden house built on granitic geology, where radon-rich well water is used. Atmospheric radon concentrations were measured over one year with passive integrated radon monitors. The monitors were distributed at several locations in the house and were replaced every two months. In order to confirm the diurnal variation and heterogeneous distribution of radon, short-term measurements were carried out accordingly. Radon, its decay products and terrestrial gamma-radiations were measured in this survey. From the long-term measurement, the radon concentration in the house ranged from 14 to 184 Bq^. m^-3with an arithmetic mean of 45 Bq^. m^-3. A radon concentration of 184 Bq^. m^-3was observed in the bathroom in spring (March-May) though the radon level was normal in the living room and bedroom. In order to characterize the house, similar measurements were conducted in several surrounding houses. There was a significant difference in radon concentration between the investigated houses. There was a spatial distribution of the radon concentration and the highest value was found in the bathroom. Radon and its decay products concentrations varied with time, which increased from midnight to morning whereas they decreased during daytime. Although the radon concentration in tap water was 1 Bq^. l^-1, a high level of 353 Bq^. l^-1was found in the well water.While well water was being used, the indoor radon concentration near the bathroom increased rapidly with a maximum value of 964 Bq^. m^-3. It is clear that the use of well water enhanced the radon level around the bathroom.     

Soil gases (222Rn, 220Rn and total radon) and 214Bi measurements across El Avila fault near Caracas, Venezuela

Summary Radon measurements were performed across two sections of the Avila fault near Caracas, Venezuela. The radon concentrations clearly showed the different tectonic features and lithology at the Tacamahaca and Spanish Trail sites. ²¹⁴Bi (U-cps) measurements also were related to the lithology. The passive radon method employed laboratory-made dosimeters with LR 115, type 2 celulose nitrate films as detectors. They were buried in the ground at 30 cm depth. While, the active radon method was performed with a Pylon radon measurement system with Lucas cells. The soil gas was also sampled at 30 cm depths, but for only one minute, which was sufficient to fill the 150 cm³ Lucas cells completely. The total radon counts were then separated into those corresponding to ²²²Rn (radon) and ²²⁰Rn (thoron) by a simple computer routine. A comparison of the active and passive methods for the Tacamahaca section over a three-month period showed that both methods could locate precisely the active fault trace.     

The effect of rock type,grain size,sorting, permeability,and moisture on measurements of radon in soil gas: A comparison of two measurement techniques

Soil surveys of radon conducted in the Coastal Plain of New Jersey, Alabama and Texas indicate that soil composition and grain size exert the strongest control on the concentration of radon measured. Soil-gas radon was measured in-situ using two techniques; one developed by G. Michael REIMER of the U. S. Geological Survey; the other developed by Rogers and Associates Engineering Corp. for use by the Environmental Protection Agency. The Reimer technique aquires a small-volume, grab sample of soil gas, whereas the Rogers and Associatess technique acquires a large-volume, flow-through sample of soil gas. The two techniques yield similar radon concentrations in well-sorted sands, but do not correlate as well for poorly sorted soils and clays.     

Radioactivity measurements as tool for physics dissemination

In general people associate environmental radioactivity with the artificial radioactivity and knows very little about natural radioactivity. Thus there is a critical need to improve nuclear physics public education. From 2005 in Italy two programs were promoted from Ministry of Education and University and National Institute of Nuclear Physics (INFN) for scientific dissemination in the field of environmental radioactivity. High school students in many Italian regions were involved in particular in indoor radon measurements. With this program students acquired awareness about the risks of inhalation of radon and its progeny and at the same time contributed to carry out radon monitoring, participating to all the experimental phases, from detectors set-up to data analysis. In particular we report about the activities carried out at Catania University and INFN division regarding a survey in the eastern Sicily. The overall monitoring, spanned over a period of 5 years, was carried out using passive nuclear track detection technique, through CR-39 dosimeters. In total about 500 detectors were placed in dwellings and schools in 57 locations. The investigated area have shown medium–high indoor radon concentrations, higher than the Italian average (70 Bq/m³). From the evaluation of the participating teachers and students, this kind of activities represents a successful strategy to enhance dissemination of physics, in particular in radioactivity topics.     

Indoor radon concentration survey in Mexico

Indoor radon evaluations in specific regions of the country have been performed in an effort to assess the magnitude of the radon problem and its public health consequences. The survey of this paper covers four large non-tropical regions of north and central Mexico, and reports the results of measurements of indoor radon concentrations in houses of towns with between 100,001 and 500,000 inhabitants. The measurements were done by using passive detectors, namely, the closed-end-cup system with CR-39 polycarbonate chips as detector material. The measurements were performed throughout the two coldest seasons (between 5 and 20°C), winter and spring, in integration periods of 28 days covering the six month cycle. The results show a moderate average radon concentration below 200 Bq·m⁻³ with occasional higher values. This is very probably due to the climate conditions and the traditional habits of open door and window ventilation. The IFUNAM (Instituto de Física, Universidad Nacional Autónoma de México) Laboratory, where the closed-end cup system for radon was developed, has gained experience though this survey and is willing to share it for future surveys at regional or national levels.     

A simple passive collector for direct measurement of radon flux from soil

A simple technique for measurement of the soil-atmosphere radon flux has been developed by fastening a charcoal canister inside a PVC cylindrical container. This device, which is deployed at the ground surface for approximately 16 hours, captures radon emanating from the soil by adsorption onto the charcoal surface. After recovery of the canister and measurement of the radon daughter activity on a NaI detector, the radon flux may be calculated if the adsorption efficiency of radon onto the charcoal is known. This parameter was determined by exposure of charcoal canisters to²²⁶Ra-spiked barium palmitate filter sources for timed intervals. Since this compound is known to emanate 100% of the²²²Rn generated during radium decay, it forms a useful flux standard. The accuracy of our flux measurements was assessed by comparison to a more established technique, the enclosed-chamber or accumulator method. Concentration measurements were made for the chamber over a less than 2-hour period while the canister flux measurements were based on single overnight deployments. The experiment was repeated 5 times at two different sites and the two techniques generally agreed within a 95% confidence interval.     

Simple and rapid methods for on-site determination of radon and thoron in soil-gases for seismic studies

The determination of soil-gas anomalies especially ²²²Rn anomalies, are important to precisely locate fault traces, as well as to investigate earthquake precursors. In this paper, we have studied and compared new rapid methods for on site determinations of radon (²²²Rn), thoron (²²⁰Rn) and total radon (²²²Rn+²²⁰Rn) in soil-gas. These new techniques pump the soil-gas continuously from the soil through a simple sampling tube to the counting cell for one-minute with discarding the excess. Then, either four one-minute counting periods (5-minute technique) or nine one-minute counting intervals (10-minute technique) are followed immediately. In all the methods, conversely to Morse"s method, the first counting period (C1) was not employed for calculations. Three calculation methods for the five-minute technique, two for the ten-minute technique and a modified Morse"s method are compared with theoretical values and different real soil-gases with different radon/thoron ratios. The affect of different flow rates of soil-gases into the counting cell was also investigated. Finally, the ten-minute technique seems to be a little more accurate, but the 5-minute technique is much more suitable for seismic field studies when a much larger number of determinations are required in a short time.     

Measurement of radon and thoron progeny size distributions and dose assessments at the mineral treatment industry in Thailand

A new portable type cascade impactor has been developed to determine the activity size distribution of radon and thoron progeny in a natural environment more efficiently. The modified impactor consists of 4 stages with a back up filter stage for the collection of aerosol samples. The aerosol cut points in the impactor are set for 10, 2.5, 1 and 0.5 μm at a flow rate of 4 L min^?1. Five CR-39 chips were used as alpha detectors for each stage. In order to separate α particles emitted from radon and thoron progeny, CR-39 detectors are covered with aluminum-vaporized Mylar films. The thickness of each film is adjusted to allow α particles emitted from radon and thoron progeny to reach the CR-39 detectors. The technique has been successfully tested in field studies, particularly inside a mineral treatment industry in Thailand to estimate doses in the working environment. The dose calculations by lung dose evaluation program showed that activity median aerodynamic diameters played a significant role in determining the particle size distributions of the attached radon and thoron progeny. The dose conversion factor determined from short term measurements due to exposure from the inhalation of thoron and its progeny was found to be 4 times higher than comparable values for radon and its progeny. The effective dose for workers exposed to radon is about 4–6 times higher than thoron.     

Indoor radon risk potential of Hawaii

Summary A comprehensive evaluation of radon risk potential in the State of Hawaii indicates that the potential for Hawaii is low. Using a combination of factors including geology, soils, source-rock type, soil-gas radon concentrations, and indoor measurements throughout the state, a general model was developed that permits prediction for various regions in Hawaii. For the nearly 3,100 counties in the coterminous U.S., National Uranium Resource Evaluation (NURE) aerorad data was the primary input factor. However, NURE aerorad data was not collected in Hawaii, therefore, this study used geology and soil type as the primary and secondary components of potential prediction. Although the radon potential of some Hawaiian soils suggests moderate risk, most houses are built above ground level and the radon soil potential is effectively decoupled from the house. Only underground facilities or those with closed or recirculating ventilation systems might have elevated radon potential.     

Environmental radioactivity survey in site studies

Systematic monitoring of Rn in soil, background gamma levels and meteorological measurements, have been conducted at the site of a Nuclear Research Center. The data cover a time period of several years. The radon in soil gas fluctuations are influenced by meteorological seasonal changes and by geophysical local parameters and they range between 1000 Bq/m³ and 18000 Bq/m³. The observed gamma levels show geographic stability; some seasonal fluctuations were observed. Data analysis indicates that no significant changes occurred at the site over the measuring time period and radiation levels and meteorological changes are moderate inducing no ecological impact on the surroundings.     

Evaluating the potential alpha energy of radon progeny

Potential alpha energy concentration of radon progeny can be measured using the alpha-spectroscopy with the silicon semiconductors detectors and the gross-counting attached with the ZnS detectors. The decay method was applied where the alpha particles emitted from the ²¹⁸Po to ²¹⁴Po were detected. In the case of the decay products, the amount and aerodynamic behavior of radioactivity are important, and also need to be measured. During the experiment, the radon gas was supplied and evaluated from the experimental room with constant concentration. Then the air sample was used as the known volume and the grab sampling technique was developed for estimating the concentration of radon decay products. However the proper calculation was applied for estimating the potential alpha energy of radon progeny through of ²¹⁸Po, ²¹⁴Pb and ²¹⁴Bi.     

A case study on the effect of water from groundwater sources on indoor radon levels

Indoor airborne radon concentration released from water was estimated over several months based on experimental measurements. When heated water including radon was used, the radon level became high in the entire house. Filling the bathtub with hot water had a strong effect on the indoor radon level. In winter, the indoor radon concentration was high due to windows being closed. The radon transfer coefficient was estimated 2.5·10⁻⁴ in this test house. This is 2.5 times higher than the average radon transfer efficiency estimated by UNSCEAR.     

Radiological characterization of commercially available “radon spa sources”

Nowadays, artificial “radon spa sources” for home baths are commercially available. Although these sources could give a potential radiation exposure to the users, few studies have been reported on their radiological measurements. In the present study, five types of radon spa sources were collected and their radiological characterization was investigated. The followings were estimated for these samples: (1) radon emanation coefficients (dry and water-saturated conditions), (2) surface γ-ray dose rate, (3) surface count rates for α- and β-rays, (4) activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K, and (5) concentrations of radon and thoron generated from the sources located in an air flow system. The activity concentrations were very high (except for one sample (named “sample B”), although radon emanation coefficient was low compared with soil. This leads to high concentrations of radon/thoron generated from the sample. The maximum surface γ-ray dose rate was observed for sample A (2.7 μGy h⁻¹). If people stay very close to the sample for a long time, the exposure might be significant.     

Indoor radon levels and natural radioactivity in Turda salt mine, Romania

The purpose of the study is to evaluate the activity concentrations and distribution of natural radionuclides in Turda salt mine having in view the development on the future of the speleotherapy in this salt mine. The radon, gamma ray and gross alpha and beta radiation measurements have demonstrated the presence of low concentrations of natural radionuclides in rock salt and soil samples collected from different points of the salt mine and sustains the development of speleotherapy in this mine.     

Variations of radon in soils induced by external factors

Experiments were designed to evaluate, in a controlled way, some of the variations that can be expected in radon concentration in soil due mainly to meteorological factors and to close spacing monitoring in the field. Electronic continuous radon monitoring and the track-etch method were used to record the radon -decay. The radon emanation in daily measurements and in long term surveys showed a general effect modulated by temperature and pressure variations. Radon monitoring in soil for nearby stations showed that a 10% range of variation can be expected with the track-etch method and as a result of non-homogeneous emanation pattern of the soil.     

Indoor radon concentration levels in Mexican caves, using nuclear track methodology, and the relationship with living habits of the bats

This work presents the results of a study of the radon levels in four caves in Mexico: Los Riscos Cave and El Judío Cave in the State of Querétaro, and Coyozochico Cave and Karmidas Cave in the State of Puebla. The measurements were made using the passive closed-end cup system, with CR-39 (Lantrack^®) as detection material, and following protocols established for the measurement of indoor radon, developed at the Dosimetry Applications Project of the Physics Institute of the Universidad Nacional Autónoma de México. The radon concentration at one location with Karmidas Cave reached more than 60,000 Bq/m³, while concentrations in the other three caves varied from 83.1–1216.0 Bq/m³, was found. During the study was observed an interesting coincidence between the radon concentration distribution inside the caves, and the bat colonies location. In general, the bat colonies are located at the medium or low radon concentration levels zones.     

成都市三环地区地基土壤氡含量测量

对成都市三环地区地基土壤中氡含量进行了检测,掌握了区域性氡含量的分布状况,探讨了整个成都市待建地坪基础中的放射性水平,并佐以对成都市地质构造的浅析,为今后城市化进程中的新建、扩建建筑的地下防氡设计提供依据,以最终提升市民的生活环境质量。     

The influence of the soil and plant natures and pollution on the radon and thoron alpha-activities inside various herbal infusions by using solid state nuclear track detectors

Uranium and thorium contents were determined in samples of various plants in the soils in which the plants were grown, and in herbal infusions made by boiling the plants in potable water, using CR-39 and LR-115 solid state nuclear track detectors. In addition, radon and thoron alpha-activities per unit volume inside the plants, soils and herbal infusions were measured. These measurements were completed by an investigation of the radon transfer between soils and plants and that between plants and herbal infusions, and also by the investigation of the influence of pollution due to different material dusts on the radon and thoron alpha activities inside the plants and their infusions.