Search

Results of estimation of radon ( Rn 222 ) emanation factors of the commonly used building materials in India are presented. All the samples were analyzed for Ra 226 , Th 232 and K 40 contents by gamma spectrometric method. Rn 222 mass exhalation rates of the various samples were determined using an Alphaguard, a continuous radon monitoring system. From the Ra 226 content and Rn 222 mass exhalation rate obtained, the Rn 222 emanation factor was evaluated for the samples. Results showed that the estimated Rn 222 emanation factors of the studied building materials and soil samples under dry condition and in powder form varied from 0.1% to 20.8 %.

Radon/thoron and their progeny concentrations were measured in different types of dwellings at different locations around industrial areas, cities and rural areas of Brahmaputra Valley of Assam by using LR-115 (type-II) plastic detector. Radon levels of different dwellings were analysed with reference to the nature of building materials, ventilation patterns and the types of underlying soil. The results were discussed under the light of exposure limits set by ICRP. The average concentrations of indoor radon and thoron varied from 39.5 to 215.2 Bq m −3 and 12.9 to 37.6 Bq m −3 , respectively. The estimated inhalation dose due to radon, thoron and their daughter products in the study areas varied from 0.53 to 1.00 μSv h −1 .

It has been well recognised all over the world that inhalation of indoor radon ( 222 Rn), thoron ( 220 Rn) and their daughter products contribute a major fraction of total dose to human beings from all possible sources of natural radioactivity. North-eastern region being in a zone of high seismicity, the indoor radon and thoron map of the region will provide a valuable database for any study related to radon and thoron anomalies. Radon enters living area mainly through floor from subsoil and building materials, and starts accumulating in poorly ventilated dwellings. So, concentration of radon and its progeny are usually higher in indoor air than in outdoor air. In the present work, an attempt has been made to assess the levels of radon, thoron and their progeny in dwellings of a few cities in the north-eastern region of India using a passive time integrated monitoring with the help of twin chamber dosimeters having LR-115 as the detector.

A series of continuous real-time radon and progeny measurements, together with passive etched-track detector measurements returning average values, were undertaken in commercial premises in Northamptonshire. Detailed measurements over several months in two separate buildings show that the level of both radon and progeny are determined to a major extent by the influence of the operation and timing of the central heating systems in place. Both buildings studied are similar in construction to many single-storey domestic properties. The operative heating system reduced the radon and progeny levels relative to the non-operating mode by over 40% during the heating period of a normal working day. The variation in temperature during this time was generally less than 3°C, indicative of a heat retentive building. Because the equilibrium ( F ) fraction is reduced during the heating period, the reductions in radon and progeny are not uniform. In the workplaces studied, the work-cycle was normally limited to 0900–1700 hours Monday to Friday, the period when the lowest values were recorded. Average daily values would therefore overstate by more than 50% the maximum potential dose during normal attendance hours. The corollary is that living under similar circumstances in domestic environments, the operation and timing of this type of heating regime may well result in higher exposure in the home than at work.

The technique of Solid State Nuclear Track Detection (SSNTD) has matured since long as a viable method of charged particle detection. The usage of this method has been successfully extended to neutron detection and gamma dose measurements as well. The etch-track mechanism has been further exploited to generate a major application area of nuclear track filters. In spite of the remarkable diversity of SSNTD applications that have emerged over the years in different fields, its potential is by no means saturated. In this article, a brief review of SSNTD applications is presented with reference to contemporary interests in science and technology. For convenience, the coverage of topics is organized under broad categories of Nuclear Physics, Materials Research, Geology, Environmental Science and allied technologies. While identifying high interest areas, those with limited but innovative applications are also mentioned. In some cases, the important results are quoted for the purpose of illustrating the strength of track detection method. In general, the presentation is aimed at providing a broad perspective of current SSNTD uses instead of detailed description of individual applications. The coverage is selective rather than exhaustive and portrays authors' preferences. Some comments related to the adoption of this technique as a mainstream method of detection are also given.

A data processing technique based on impulse responses from multivariable time series was applied to radon data. It was found that soil gas radon at 50 cm depth was affected more by meteorological parameters than at 100 cm depth. This fact together with the fact that the radon change at the latter depth was larger when an earthquake occurred, radon measurement at 100 cm depth was tested as an earthquake precursor. The result showed correlation between radon anomalies and earthquake events.

Radon determination in soil with Solid State Nuclear Track Detectors (SSNTDs) provides information regarding the evolution of this gas on a long-term basis. When SSNTDs are exchanged during field surveys the radon atmospheres in the detecting chambers are perturbed. In addition, frequent retrieval of the detectors in the field often requires expensive logistics. In order to improve field work, an SSNTD automatic exchanger with several months autonomy has been designed and tested. The performance of the device under laboratory and field conditions, is presented.

The concentrations of radon and radon daughters in Syrian homes were studied since 1994 (Othman et al ., 1996). In this work too, the relationship between the parameters of some houses in Damascus city and radon together with radon daughters concentration were studied. These houses were classified into three types depending mainly on the house design. The radon concentration measurements were carried out in different places inside these houses using solid state nuclear track detectors. In addition a gamma survey meter was used to determine gamma dose rates inside the studied houses and they were compared with radon concentrations. Scintillation technique was used to monitor the variation of radon and radon daughter concentrations during the day inside one type of houses. The correlation between radon concentrations and age of houses in Damascus city was also checked in this study.

Indoor radon survey in the town of Podgorica, capital of Montenegro, was performed in winter season 1994–1995. The town houses were classified on the basis of their construction materials and techniques in 4 distinct types. Radon was measured in 110 dwellings, selected with respect to the types and locations of houses. Measurements were carried out by cellulose nitrate track detectors, exposed for 90 days in living-rooms on ground floors. Equilibrium equivalent concentrations of radon are found to be in (4 – 453) Bq/m 3 range, with a median of 26.4 Bq/m 3 . They belong to a log-normal distribution (geometric mean: 21.8 Bq/m 3 , geometric standard deviation: 2.20 Bq/m 3 ). The detached houses built of bricks have the highest average indoor radon level, and the apartment houses made of concrete and bricks, with plaster on the walls, the lowest one.

The first systematic indoor radon survey in Kosovo and Metohia, Yugoslavia, was performed with passive radon dosimeters of the J. Stefan Institute utilizing CR-39 detector. Some regions, where houses are built from stone with a relatively high uranium concentration (of the order of 10−5 g g−1), could be classified as radon prone areas (radon concentration around 800 Bq m−3). With the same dosimeter the radon activity concentration was measured in various levels of the Trepca lead and zinc mines. The average radon concentration was found to be relatively low (200–800 Bq m−3) and practically independent of the depth in the mine.

A controlled radon chamber was used to test the detection performance of a portable active radon detector. The elapsed time to reach detection equilibrium with the radon atmosphere was three hours; the radon detector was sensitive to daily temperature changes. After using the radon detector three hours waiting time is required to place it in a new radon environment.

Two active volcanoes, the Popocatepetl in Mexico, and the Piton de la Fournaise on the island of La Reunion, France, have been monitored for soil radon for several years. The Popocatepetl, located 60 km from Mexico City, started an eruptive period in December, 1994. Two radon-in-soil monitoring stations are operated there, since 1993. The behaviour of soil radon showed an increase as a function of the eruptive phase. The Piton de la Fournaise volcano has also been under survey for several years. A radon network based on 20 Clipperton II automatic probes was set on July, 1994. Since then, the volcano has entered a quiescence phase. Thus it has been possible to draw the pattern of the radon behavior under the influence of atmospheric conditions.

Starting from August 1993 until July 1994, continuous radon activity concentrations have been monthly measured in the air of two archaeological sites namely, Kom El-Shukafa Catacombs and Serapis Temple in Pompey's Pillar area in Alexandria. The radon activity concentrations were measured using the diffusion cup technique and with LR 115 nuclear track detectors used inside and outside each cup. Monthly variation of radon activity concentrations were observed in the two places. The average value of radon activity concentrations ranged from 34–267 Bq m −3 in Kom El-Shukafa Catacombs and from 22–1234 Bq m −3 in Serapis Temple. The average effective equivalent dose is discussed as well.

Inhalation of radon and its daughter products makes the major contribution to the total exposure of population to natural radiations. In implementing a complex ecological survey, concentrations of radon and its daughter products were measured in different regions of Russia, namely, in St.-Petersbourg Region, in Central Territories, and in Altay Territory. Two most suitable low-price versions of the dosimeters for measuring environmental radon concentrations based on track-etch and activated-charcoal detectors were used. The radon daughter product activity was calculated with an equilibrium factor of 0.5. Indoor measurements were taken in more than 1000 dwellings and public and industrial buildings of 21 towns and villages. The track chambers were exposed for about 2–3 months, and the charcoal detectors for 6–10 days. The actual radon and daughter-product concentration levels is presented and analyzed.

The project is supported by the EU-programme Human Capital and Mobility. The project intends to improve the understanding of the specific behaviour of the radon gas. The research will consequently focus on parameters or effects affecting radon concentration levels and their variation in buildings as a function of existing and previous variations of radon in the underground, in addition to the radon component from the building materials and environmental artificial radon sources coming from industrial processes like mining and metallurgy. The programme is to carry out an intercomparisonal experimental survey Lund-Kiel-Leipzig-Montpellier-Barcelona-Rome including both regular dwellings and instrumented “test houses” under various meteorological, geological and environmental conditions including the habits of the inhabitants. The radon levels will be measured indoors and in the subsoil using both track films and electronic devices. This should lead to a general model pertinent to variations of the radon concentration in houses.

The seasonal variations of indoor radon, thoron and their progeny levels were studied in 20 houses situated in the oil-rich areas of Digboi of Upper Assam. Solid-state nuclear track detectors LR-115 type II were exposed using plastic twin chamber dosemeters to record tracks formed by the two gases and their progeny. Inhalation doses were found out using extracted equilibrium factors and ventilation rates. The random (counting) errors in track densities were determined.

Indoor radon/thoron have been recognised as one of the health hazards for mankind. Common building materials used for construction of houses, which are considered as major sources of these gases in indoor environment, have been studied for exhalation rate of radon/thoron. ‘Can’ technique using plastic track detector LR-115 type-II has been used for measurement. Exhalation rates for radon and thoron have been found to be varying from a minimum value of 0.024 and 29.4 Bq m −2 h −1 for cement plastered brick to a maximum value of 0.16 and 692.2 Bq m −2 h −1 for unfired brick, respectively. Exhalation rate for thoron has been found to be several times higher than that for radon. Measured exhalation rates for thoron indicate significant presence of thoron in indoor environment which is also supported by indoor measurements of thoron and its progeny.

Active interference of man into nature and scientific-technical progress leave a notably negative trace on the surface of the Earth. Here we can refer radioactive interments, mines for launching cosmical objects and etc. We, the inhabitants of Tajikistan are worried with radioactive (solid, fluid) interments and agents in the north of the country. It is known that Northern Tajikistan was a main purveyor of uranium for the atomic units of the former USSR. Here there were being intensely wrought out the uranium layers. If in 1945 they had got 7 tons of pure uranium, to the year 1953 the volume of the metal output was amplified up to 400 tons per year. Because of it there had been accumulated a certain store of radio-active agents both in the mines and on the roads, along which the ore being transported, for the hundreds of years ahead (Murtazaev et al., 1994). The ex-USSR having created its own might and glory left us alone with radioactive interments, agents, contaminations; thus it added new ecological problems of international level to those of social order we have had already. Some of these solid radioactive agents which are around the towns of Khujand and Chkalovsk, are strewn with inert soil, the thickness of the latter being 0,5 m; others need strewing, but as for fluid radioactive agents, a lot of problems are caused. There fore, in our opinion, constant observance over α, β, γ backgrounds of fluid radioactive agents is necessary.