A. Poffijn

The compact disk as radon detector--a laboratory study of the method.

Abstract— The radon absorption ability and the track etch properties of the polycarbonate material of commercial compact disks make them very useful as sensitive retrospective 222Rn detectors. The basic idea is to remove, after exposure, a surface layer that is thicker than the range of the alpha particles of the 222Rn and 220Rn progenies and to count the electrochemically etched tracks at the corresponding depths (>80 &mgr;m). The effects on the response due to differences in pressure, temperature, and humidity have been studied experimentally. The effect of the growing of 210Po after long-term exposures was also estimated. The effect of all listed factors except the temperature is either absent or restricted to maximum—about 10% for the very extreme cases. The variation of the response at 83 &mgr;m depth over the temperature interval 15–25°C is ±12% around the 20°C value. The dependence of the calibration factor on the etched depth beneath the surface was studied at 4 different temperatures within the range expected indoors. The results show that the depth dependence is exponential with the parameters of the exponent also being dependent on the temperature. In practice, using the track density obtained in two or more depths beneath the compact disk’s front surface, an a posteriori temperature correction could be made. By this correction it is possible to substantially reduce the bias in the results due to the unknown temperature during exposure. The results imply that by using home stored compact disks long-term retrospective 222Rn measurements could be made with an uncertainty that could be potentially better than 10%. The useful range of the method starts at about 3 Bq m−3 (for 10 y exposure time) and appears to cover practically the whole range of indoors 222Rn concentrations.

Indoor radon detected by compact discs

An approach for a precise retrospective assessment of the indoor radon exposure using commercial compact discs (CDs) is proposed. It is based on the remarkable radon absorption and α track-etch properties of polycarbonate — the basic material of the CDs. The experimental results indicate that the useful range of this approach is able to cover practically the entire range of indoor 222Rn concentrations.

3-D Confocal microscopy track analysis: a promising tool for determining CR-39 response function

Abstract A new method based on the use of the confocal microscope is described in order to evaluate the CR-39 response function for Li-7 ions with an incident energy of 10.77 MeV . This method uses the formulations developed by Fromm et al. and considers two etching velocities: V B represents the bulk etch rate and remains constant, and V T the track etch rate, which varies along the particles path. The confocal microscope seems to bring big improvements for track analysis. The first results of V T versus the particle range are presented and compared with the curves obtained by the sequential etching method. The obtained V T are plotted and compared to LET, REL 350 and the cumulative radial dose.

Watching at the correlation between the specific track-etch rate and the primary physical parameters of the swift ion interaction with the CR-39

Abstract Analysis of etched nuclear tracks in CR-39 solid state nuclear track detectors has recently been made possible by the confocal microscope. This recent innovation has opened up some particularly interesting perspectives. The main originality of this microscopy technique is that it makes it possible to work on numerical, three-dimensional images of chemically etched nuclear tracks in the CR-39. We have studied the performances of this new approach for light ions (H, He, Li and C) with kinetic energies typically of the order of the MeV per nucleus. First, we determined the response functions of the CR-39 for these ions. We were then able to show that aside from decreasing the analysis time of traditional methods, the confocal microscope greatly increases the sensibility of the detection. The aim of this study was to find a correlation between the response functions and the primary physical parameters of the interaction between the ion and the material, such as the linear energy transfer (LET), the restricted energy transfer (RELω0), the integrated radial dose or the rate of ionization. Although these parameters presented a strong resemblance to the experimental response functions (they are all “Bragg” curves), none of them were correlated to the response function in an unambiguous way.

A passive radon dosimeter based on the combination of a track etch detector and activated charcoal

Abstract The aim of this work is to test a combination of a Makrofol track detector with a new type of charcoal (Carboxen-564) to design a personal radon dosimeter. The intention is to use this dosimeter as a personal radon dosimeter to measure the monthly radon exposure in workplaces, especially when the occupancy is not ecactly known. The proposed combination was exposed to low and high concentrations of radon in a large range of relative humidity (RH). For the optimal layer thickness, a charcoal bed of 2.2 mm, a specific track density of 5.1 tracks cm −2 /kBq h m −3 was obtained. For a monthly working exposure (170 h) at an average radon concentration of 100 Bq/m 3 , this means 87 tracks/cm 2 or 10 times the background of the Makrofol detector, with a statistical uncertainty of 15%.

Study of a passive detector for retrospective radon measurements

Abstract It is well known fact that radon is the most important factor in the natural radiation background. For complete risk estimation we need information about the past radon exposure. As suggested by C. Samuelsson et al . in 1988, the activity of the implanted radon daughter 210 Po can be used to reconstruct the radon activity over the past decades. For large scale surveys in dwellings a passive polycarbonate detector has been investigated. A technique of heating these detectors to temperatures up to 110°C has been tested to reduce the number of background tracks, present in the detector after long time storage.

Study of the atmospheric 85Kr concentration growth in Gent between 1979 and 1999

Abstract Since 1979, the atmospheric 85 Kr concentration has been monitored at our laboratory. The extensive data set, obtained in this way, has been statistically analysed to examine the degree of atmospheric 85 Kr concentration growth over the past decades. The results were compared with those values found in the literature and with calculations of the 85 Kr emission from the reprocessing plant of Cap La Hague.

Semi-automated analysis of three-dimensional track images

In the past, three-dimensional (3-d) track images in solid state detectors were difficult to obtain. With the introduction of the confocal scanning laser microscope it is now possible to record 3-d track images in a non-destructive way. These 3-d track images can latter be used to measure typical track parameters. Preparing the detectors and recording the 3-d images however is only the first step. The second step in this process is enhancing the image quality by means of deconvolution techniques to obtain the maximum possible resolution. The third step is extracting the typical track parameters. This can be done on-screen by an experienced operator. For large sets of data however, this manual technique is not desirable. This paper will present some techniques to analyse 3-d track data in an automated way by means of image analysis routines. Advanced thresholding techniques guarantee stable results in different recording situations. By using pre-knowledge about the track shape, reliable object identification is obtained. In case of ambiguity, manual intervention is possible.

Theoretical study of the relation between radon and its long-lived progeny in a room.

We present a theoretical study of the complex relation between radon and its long-lived progeny implanted in glass surfaces. The well known (extended) Jacobi room model, which is normally used to describe radon and its progeny in a room, was transformed into a two-parameter model revealing a linear correlation between long term radon exposure and surface activity due to implanted radon decay products. Furthermore, this new approach made integration into a Monte Carlo simulation possible so that the large variation of different room model parameters could be taken into account. This allowed the calculation of a probability distribution for radon exposure from the measurement of the implanted 210Po activity. The availability of a 95% confidence interval for the radon exposure is valuable in the application of retrospective radon assessment in epidemiological studies.

Studies on radon adsorption characteristics of different charcoals used as amplifiers for the track detectors.

Abstract Ten sorts of charcoals were studied regarding their use as amplifier in the design of a personal dosimeter. It consists of a combination of a Makrofol detector and activated charcoal. The calibration factor for the Makrofol using the charcoals as an amplifier is about ten times higher comparing with an exposure without charcoal. The best results were obtained with Carboxen 563. The background radioactivity of charcoals must also be considered in the dosimeters design.