G. Jönsson

Radon gas — where from and what to do?

Abstract Radon is sort of an outsider in nature because it is the only element that is a gas in a long chain of radioactive decays. For an individual person, exposed to radon gas for a long time, there is an increase in the risk for growth of a lung cancer. Radon may also be a causative factor for other kinds of cancer, maybe by synergy with other pollutants like tobacco smoke. Solid State Nuclear Track Detectors (SSNTD) have become an important tool in the investigation of the presence of radon gas, not only in indoor air but also in soil air. Important characteristics of radon and its progeny are discussed in this report. The use of the plastic film LR115-II in radon and radon daughter detection is also reported. Some measurement results of radon will illustrate the usefullness of SSNTD concerning the radon problem.

Radon emanation from soil samples

Abstract The soil or bedrock beneath a building is one of the sources of radon gas in the indoor air. The 238 U content of samples of the soil or the bedrock can be measured by gamma ray spectrometry and is of interest because the uranium content in the soil is a precursor of the presence of the radon gas in the soil. The emanation of radon gas from different types of material can be estimated to some extent if the content of 238 U of a sample is known and the 226 Ra content is only minorly affected. The true emanation is, however, affected by various parameters. One of these parameters is the possibility or not for the gas to come out from the grains into the air in the space between the grains of the sample. In this study we report the results from measurements of radon gas emanating from samples of soil frequent in the Lund region in Sweden and in the Barcelona region in Spain. As soils have different grain size it is important to know the type of soil. The 238 U content of the soil is measured with gamma ray spectrometry. The radon measurements are made by Kodak plastic film in closed cans, filled with the soil according to a technique, developed for radon measurements in water samples. The result shows, that the combination of grain size and uranium content is important for the emanation of the radon gas from the grains of the soil.

Soil radon levels measured with SSNTD's and the soil radium content

Abstract The source of the radon gas 222 Rn in the ground air is the soil and the bedrock underneath. The potential radon level in the ground is given by the content of 226 Ra in the ground. The presence of 226 Ra is in turn dependent on the amount of 238 U in the ground, and these two isotopes are not always found to be in equilibrium in a sample of soil or bedrock. Especially if the soil is washed out, the radium content may be reduced. When the soil is the relevant source of the radon gas, it is interesting to look for a possible relation between the radon level and the radium content of the soil. In this paper we report on measurements of soil radon level carried out with SSNTDs at several European sites. Soil samples were collected at these sites and analysed with gamma spectrometry to determine their radium content. A comparison of the different degree of disequilibrium of radon, defined as the ratio between the actual and the secular equilibrium-with-radium soil radon concentration, found at the different sites and depths is presented. The influence on the result of soil type and climate is briefly discussed.

Soil radon depth dependence

Abstract The knowledge of the soil radon levels is important for the planning and construction of new buildings in order to estimate the radon risk and to classify the ground for construction purposes. The purpose of this investigation was to study in situ the radon levels at various depths 0– 2 m in terrain where the geology is comparatively uniform. The data from the measurements was fitted to simple functions in order to facilitate future extrapolations of radon levels from various depths to 1 m at measurements anywhere. The plastic film Kodak LR 115 was used as the detector of the radon levels at four different depths in the interval 0– 2 m . The measurements were made along a 2200 m long profile at 16 different points.

Modelling of solid state nuclear track detector devices for radon measurements

Abstract Theoretical analytical calculations of the radon registration have been performed for the solid state nuclear track detectors (SSNTD) LR-115 Type II (peliculable) produced by Kodak-Pathe (France). Known and measured properties of LR-115 together with the well established etching theory using “Huygens principle” were used to carry out these detailed calculations for different types of exposure devices for indoor room and outdoor soil measurements. The results of these modeling calculations are compared with experimental calibration measurements and show good agreement.

Experimental study on the aging process of the LR 115 cellulose nitrate radon detector

Abstract An experimental determination of the aging process of cellulose nitrate detector material was based on the examination of special properties of the LR 115 solid state nuclear track detectors (SSNTDs) of various ages up to 18 years. The examined relevant parameters are the bulk etching rate vb and the track etching rate vt. These parameters are responsible for the appearance, the size and the registration efficiency of tracks of α-particles from radon gas in the detector. To find a correlation between these material parameters and the detector sensitivity an experimental calibration of indoor room and outdoor soil detector devices based on LR 115 took place at the Umweltforschungszentrum Leipzig-Halle (Germany). To avoid routine calibration work in external radon exposure facilities a correction of the age dependent calibration factors with the material parameters measured in ones own laboratory was targeted. In this study a general age dependence, however, was not found. The following statements for practical applications can be made. (i) the bulk etching rate vb for detectors of the same batch has a depth dependence and this dependence is constant over 2 years (LR 115 September 1994). (ii) detectors of different batches older than 5 years and stored at room temperature show an odd vb behaviour when vb is used for describing track shapes. (iii) the calibration factor of detectors of different batches that were stored at about +4°C is constant over 5 years (LR 115 September 1994 and February 1999, Table 2). The conclusion is that LR 115 detectors not older than 5 years and stored in a refrigerator at about +4°C should be preferred for radon measurements. Furthermore these detectors should be recalibrated every year and the microscope work of this calibrations should be performed by the same person who performs the measurements. In addition, a phenomenon related to fundamental track formation mechanisms was found, that the time straggling of the time tthrough when vertical tracks penetrate the 12 μm thick detector layer is independent of the age of the detectors and the energy of the α-particle at the detector surface.

The nuclear track detector : A tool in radon measurements

The nuclear track detector is an excellent tool as well in large scale radon surveys as in single radon measurements indoors or in soil. In this report there are discussions concerning detectors based on Kodak LR 115-II film. The items are the following: a) Some properties of the detectors, b) The calibration of the detectors, c) The use of the detectors and interpretation of measured radon levels.

Criteria for indoor radon concentration — an experimental study considering especially the Leipzig-Halle brown coal area

Abstract 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.

Application of a radon model to explain indoor radon levels in a Swedish house

Abstract Radon entry from soil into indoor air and its accumulation indoors depends on several parameters, the values of which normally depend on the specific characteristics of the site. The effect of a specific parameter is often difficult to explain from the result of indoor radon measurements only. The adaptation of the RAGENA (RAdon Generation, ENtry and Accumulation indoors) model to a Swedish house to characterise indoor radon levels and the relative importance of the different radon sources and entry mechanisms is presented. The building is a single-zone house with a naturally-ventilated crawl space in one part and a concrete floor in another part, leading to different radon levels in the two parts of the building. The soil under the house is moraine, which is relatively permeable to radon gas. The house is naturally-ventilated. The mean indoor radon concentration values measured with nuclear track detectors in the crawl-space and concrete parts of the house are respectively 75±30 and 200±80 Bq m −3 . Results of the model adaptation to the house indicate that soil constitutes the most relevant radon source in both parts of the house. The radon concentration values predicted by the model indoors fall into the same range as the experimental results.

Experience from using plastic film in radon measurement

Abstract Plastic film is a useful detector of radon gas. The method of detection of the gas is used for several decades to measure radon concentrations both indoors and in soil. Experiences from radon measurements in Sweden indoors, in soil and in water using the plastic film Kodak LR 115-II are discussed in this report. Some examples are given from various projects. One example is taken from a large scale mapping of indoor radon levels in houses, where the building material is the main source of radon. In anotther example the measurements from a large scale soil radon mapping are discussed. The use of the plastic film for measurements of radon levels in water is also discussed. All the investigations are made in order to give the authorities concerned information of the radon situation and to study the connection between high indoor radon levels and various types of cancers.