Comparison of retrospective and contemporary indoor radon measurements in a high-radon area of Serbia.

In Niska Banja, Serbia, which is a high-radon area, a comparison was made between two retrospective radon measuring methods and contemporary radon measurements. The two retrospective methods derive the radon concentrations that occurred in dwellings over longer periods in the past, based on the amount of trapped (210)Po on the surface of glass objects (surface traps, ST) or in the bulk of porous materials (volume traps, VT). Both surface implanted (210)Po in glass objects and contemporary radon in air were measured in 46 rooms, distributed in 32 houses of this radon spa-town, using a dual alpha track detector configuration (CR-39 and LR115) and CR-39 track etched detectors, respectively. In addition to the use of surface trap measurements, in 18 rooms (distributed in 15 houses) VT samples of suitable material were also collected, allowing to compare ST and VT retrospective radon concentration estimates. For each room, contemporary annual radon concentrations (CONT) were measured or estimated using seasonal correction factors. The distribution of the radon concentration in all data sets was found to be close to lognormal (Chi-square test>0.05). Geometric means (GM) are similar, ranging from 1040 to 1380 Bq m(-3), whereas geometric standard deviations (GSD) for both the retrospective methods are greater than for the CONT method, showing reasonable agreement between VT, ST and CONT measurements. A regression analysis, with respect to the lognormal distribution of each data set, shows that for VT-ST the correlation coefficient r is 0.85, for VT-CONT r is 0.82 and for ST-CONT r is 0.73. Comparison of retrospective and contemporary radon concentrations with regard to supposed long-term indoor radon changes further supports the principal agreement between the retrospective and conventional methods.

Development of a low cost, GPS-based upgrade to a standard handheld gamma detector for mapping environmental radioactive contamination.

A low cost extension to a standard handheld radiation monitor was developed, allowing one to perform outdoor georeferenced gamma measurements. It consists of a commercial wireless Bluetooth GPS receiver, a commercial RS-232 to Bluetooth converter combined with a standard Bluetooth enabled pocket personal computer (PPC). The system is intended for use in difficult to access areas, typically for foot campaigns. As the operator walks, a straightforward homemade visual basic program alternately reads GPS position and gamma dose rate into the PPC, creating a data log. This allows a single operator on foot to map between 50 and 200 ha of environmental radiation per day in very rugged areas, depending on the accessibility of the terrain and the detail required. On a test field with known contamination, a spatial precision of about 5-10 m was obtainable. The device was also used to reveal complex contamination patterns in the flooding zones of a radioactively contaminated small river.

Radiological health risk evaluation of radium contaminated land: a real life implementation.

A plot of land, currently used for dairy farming, has been contaminated over the years with radium due to the operation of one of the world's largest radium production plants. Within the framework of a global remediation approach for the plant surroundings, the land owner needed advice for a future destination of the land. Therefore, the radium contamination was accurately mapped, and on the basis of its severity a practically feasible subdivision of the land into four plots was proposed. For all four plots, the radiological risk was evaluated for the current type of land use and for possible alternative types. Hence a clear and useable advice could be formulated to the authorities reconciling public health, economic and practical issues.

Field experience with volume traps for assessing retrospective radon exposures.

Approximately 200 volume traps were retrieved from dwellings in various radon prone areas in Europe. They were analysed for the purpose of retrospective radon assessment. Emphasis is put on specific problems encountered when using field samples as opposed to laboratory exposed samples. It was seen that in very dusty circumstances, direct penetration of radon decay products from the outside to the centre of the volume traps calls for extra caution. Rinsing the samples is proposed as a solution and was tested in field and laboratory conditions, showing good results. An attempt was made to give an assessment of the achievable accuracy of the method. Where possible, the volume trap retrospective results were compared with contemporary measurements or to retrospective results from surface traps. The overall impression is that although volume traps are sometimes hard to find in the field, the high reliability of the results makes it well worth the effort.

Retrospective assessment of historic radon concentrations in Norwegian dwellings by measuring glass implanted Po-210--an international field intercomparison.

The first Norwegian study of historic radon concentrations in 17 dwellings in the high radon areas in Norway has been conducted as part of an international field intercomparison during 1998. The retrospective radon concentration is estimated via measurements of Po-210, the long-lived decay product of Rn-222 implanted in glass surfaces of objects like pictures, mirrors, cabinet-glass, etc. the method called 'surface trap'. Three different surface trap techniques to assess the implanted Po-210 activity and two different procedures to estimate retro radon from Po-210 data were used. The Po-210 and the retrospectively estimated radon results agree reasonably well over a wide range of concentrations. Historic radon concentrations were also estimated from analysis of a smaller number of 'volume trap' samples (pieces of spongy materials), and the results compared to those from 'surface traps'. The retro radon results correlate with contemporary radon results with a correlation coefficient of 0.877. To evaluate uncertainty in Po-210 measurements due to varying position on the glass a study of spatial homogeneity of three sample glasses was conducted and variations between 12% and 18% were found.

Integrated natural radiation exposure studies in stable Yugoslav rural communities.

The results of field investigations of natural radiation exposures of the general population in two stable rural communities in Yugoslavia are presented. The principal emphasis was on exposures to contemporary indoor radon, but measurements of external penetrating radiation absorbed dose rates in air were carried out in the majority of cases. In addition, in a limited number of dwellings, measurements of thoron gas concentrations were made. By means of making a series of sequential 3-month radon measurements, both seasonal variations and annual average radon levels in the dwellings were determined. Using passive alpha track detectors, individual radon and thoron indoor concentrations as high as 9591 Bq m(-3) and 709 Bq m(-3), respectively, were detected while absorbed dose rates in air in the dwellings as high as 430 nGy h(-1) were recorded. On the basis of these different types of measurements, assessments could be made of the integrated natural radiation exposures being received by the populations. In addition to contemporary radon measurements, retrospective radon exposure assessments in most of the dwellings were made on the basis of measurements of 210Po concentrations in both surface (glass) traps and in volume (porous materials) traps. A description is given of the sampling strategies and protocols used in this field work. It is shown that at least one stable rural community receiving high natural radiation exposures, has been clearly identified and plans for future health investigations of the population there are outlined.

The usability of wood as a volume trap for the purpose of retrospective radon exposure assessment.

The possibility of using wood samples as a retrospective radon monitor was investigated. Retrospective radon monitors are based on the analysis of the enhanced 210Po content of the bulk of the sample as a result of radon exposure. Several wood samples in different sizes and shapes were tested for their radon penetrability and the speed at which radon can diffuse throughout the material. Also, the volume ratio of air to solid material and the natural occurring 210Po background were determined. It was seen that only in fairly exceptional cases wood can be used as an acceptable volume trap. This is mostly due to the high and variably occurring natural 210Po background in wood samples with respect to the expected increase in radon-related 210Po due to common radon concentrations in dwellings.

Radium contamination of the banks of the river Laak as a consequence of the phosphate industry in Belgium.

For over half a century, phosphate ores of marine origin, containing 226Ra, have been processed in Belgium to produce calcium phosphate for use in cattle food. As a result, the waste water containing 226Ra were discharged into two little rivers, one of which is the Laak. The purpose of this study was to chart the radium contamination of the river banks and some areas that are regularly flooded by the river. It was seen that enhanced concentrations of 226Ra do occur along the river banks, but that the contaminated area is mostly confined to a 10 m strip on both sides of the river, even in the flooding zones. At present, no dwellings are present on top of the contamination and no crops for direct human consumption are grown there, so there is no immediate threat to the population.

Retrospective radon assessment by means of 210Po activity measurements.

A method for retrospectively assessing the average radon concentration in a dwelling, for a period as long as 40 years or more, is described. It is based on the free penetration of radon gas into bulky spongy materials called volume traps, and subsequent trapping of radon decay products inside them. This leads to a build-up of 210Pb, a radon decay product with a half life of 22.3 years, which reaches an equilibrium with the alpha emitter 210Po, indicative of the average radon concentration over the exposure period. The stuffing of mattresses, chairs, cushions, etc. can be considered a good volume trap. A chemical separation procedure is described, transforming the volume trap into a 210Po alpha source, whose activity is determined through alpha spectroscopy. The technique has been applied in over 300 samples, retrieved from dwellings in Serbia, Germany, Norway and Sweden. The technique has proven to be very robust and reproducible. In cases where radon data were available during the exposure period of the volume trap, a remarkable agreement was found. The best volume traps appeared to be polyester sponges found in many stuffings. The major drawback is the destructive nature of the method, its major advantage is the direct relationship between the radon gas and the 210Po signal. The technique can be useful in epidemiological studies of the lung cancer risk from indoor radon, for assessing the long term radon exposure.

Anomalous results with the widely used NRPB/SSI-type passive radon dosemeter.

In an industrial hall, with large variations of radon concentration within minutes, simultaneous measurements were done with two types of passive radon detectors and an active radon measuring device. The widely used passive radon detector of the National Radiological Protection Board (NRPB) [Health Protection Agency (former NRPB) (HPA)]/Statens strålskyddsinstitut (Swedish Radiation Protection Institute) (SSI) type produced anomalous results, seemingly uncorrelated to the radon concentration which was in the order of hundreds of becquerels per metre, usually underestimating but occasionally overestimating. We tried to reproduce similar exposure characteristics in our laboratory, but failed to reproduce the anomalous readings. We suspected, but could not prove, that the anomalous results were due to the combination of high radon concentration gradients, with pressure-driven air exchange between the inside of the detector holder and the outside atmosphere. Moreover, this theory was at least partly contradicted when we drilled holes in the detector holder. Although of interest, this effect is not likely to have substantially influenced any radon surveys, given the unusual nature of the exposure that caused the effect.

Radiological impact of almost a century of phosphate industry in Flanders, Belgium.

In Belgium, since about 1920, the phosphate industry has been an important industrial activity. It is principally situated in Flanders, the northern part of Belgium, and produces mainly phosphoric acid, fertilizers, and cattle food. At its height, between 1980 and 1990, it processed between 1.5 and 2.0 Mt of phosphate ore of varying origin per year. In total, more than 60 Mt of ore were handled, containing about 72 TBq of 226Ra and 3.5 TBq of 232Th. Three different processing techniques in six large production sites gave rise to 50 Mt of phosphogypsum and 2.7 Mt of calcium fluoride sludge, all mainly stored on large deposits. In addition, limited recycling of phosphogypsum as building material has occurred in the past. Also, 10 Mt of phosphogypsum was discharged into a large tidal river. One plant still produces 0.25 Mt of gypsum per year. Liquid effluents, containing 13 TBq of radium chloride, were discharged into two small rivers, thus contaminating over 200 ha of land. Approximately 8 TBq of 226Ra and 0.6 TBq thorium ended up in finished products such as fertilizers. Despite these large production figures, so far the radiological impact for the Flemish population has been limited, but this might worsen in the future. The major risk consists in establishing residential areas on land that is contaminated with 226Ra because of liquid effluents or on forgotten gypsum deposits. Doing so might lead to enhanced indoor radon concentrations. In three isolated cases, we found houses built on gypsum deposits where the increased indoor radon levels raised the annual radiation dose to the inhabitants by about 4 mSv.