Geert Meesen

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.

Different replication characteristics of historical pseudorabies virus strains in porcine respiratory nasal mucosa explants

Different alphaherpesviruses, including pseudorabies virus (PRV), are able to cross the basement membrane barrier in nasal respiratory epithelium. As a first step in investigating this invasion process, a detailed quantitative analysis system was set up to determine the kinetics of horizontal and vertical virus spread in nasal explants, using the virulent PRV strain 89V87. Plaque latitudes, total depths, depths measured from the basement membrane and volumes were determined at 0, 12, 24 and 36h post inoculation (pi). PRV 89V87 was found to spread in a plaquewise manner and to cross the basement membrane between 12 and 24hpi. During the 1960s-1970s, an increase in PRV virulence has been reported. To analyse potential differences in efficiency of infection and spread for different historical PRV strains, single infected cells and plaques of infected cells were quantified at 12 and 36hpi in nasal mucosa explants for seven European PRV strains, isolated in the 1960s (Becker, NIA1), the 1970s (NS374, NIA3, 75V19) and later (89V87, 00V72). All viruses were used at second passage in cell culture, except for the Becker strain, which had an unknown passage history. Older strains, Becker, NIA1 and/or NS374, showed lower numbers of primary infectious centers, lower capacity to form plaques and/or lower capacity to cross the basement membrane. The observed differences in virus-mucosa interactions may aid in understanding the virulence increase of PRV. The quantitative assay established here will be of use in unravelling the mechanism of alphaherpesvirus-mediated invasion through the basement membrane.

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.

High content analysis of human fibroblast cell cultures after exposure to space radiation

Abstract Space travel imposes risks to human health, in large part by the increased radiation levels compared to those on Earth. To understand the effects of space radiation on humans, it is important to determine the underlying cellular mechanisms. While general dosimetry describes average radiation levels accurately, it says little about the actual physiological impact and does not provide biological information about individual cellular events. In addition, there is no information about the nature and magnitude of a systemic response through extra- and intercellular communication. To assess the stress response in human fibroblasts that were sent into space with the Foton-M3 mission, we have developed a pluralistic setup to measure DNA damage and inflammation response by combining global and local dosimetry, image cytometry and multiplex array technology, thereby maximizing the scientific output. We were able to demonstrate a significant increase in DNA double-strand breaks, determined by a twofold increase of the γ-H2AX signal at the level of the single cell and a threefold up-regulation of the soluble signal proteins CCL5, IL-6, IL-8, β-2 microglobulin and EN-RAGE, which are key players in the process of inflammation, in the growth medium.

Digital titration: Automated image acquisition and analysis of load and growth of Chlamydophila psittaci

Traditionally, the amount of infective chlamydiae in a given sample is determined by inoculating dilution series into cell cultures and physically counting chlamydial inclusions. This approach is time consuming, tedious, and error prone, mainly when dealing with high titers. Therefore, this paper describes a largely automated technique that was developed to standardize the determination of chlamydial load in vitro. Cells are fixed at 36 h post‐inoculation and bacteria visualized using standard immunological detection methods. Consequently, for 81 microscopic fields, an image is recorded at the interpolated focal plane. These images are then automatically processed using an ImageJ plugin and the obtained results are imported into Excel to determine the number of inclusion forming units per mL in the sample. The main advantage of this technique is that no or minimal sample dilution is required, thus minimizing dilution errors. In addition, this technique was employed during the early, middle and late growth stages of the chlamydial developmental cycle and results correlated well (P < 0.01) with 16S rRNA values from previous experiments, thereby proving its suitability to follow chlamydial growth in vitro. The method described is highly suitable for high throughput titration of cell culture inoculated samples and assessment of possible antichlamydial effects of novel compounds throughout the chlamydial growth cycle. Microsc. Res. Tech., 2009.

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.

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.