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Radiocesium contamination of air, rain, grass, milk and humans in Belgium from the late 1950s to present was measured. The main sources of fallout were atmospheric nuclear weapons tests and the Chernobyl accident; in Belgium the average impact of the first on the human body burden was more than six times higher. The geographical distribution of radiocesium fallout in Belgium was surveyed by means of in-situ gammaspectrometry with HPGe detectors.

This paper reports on a new utility for development of computational phantoms for Monte Carlo calculations and data analysis for in vivo measurements of radionuclides deposited in tissues. The individual parameters of each worker can be acquired for an exact geometric representation of his or her anatomy, which is particularly important for low-energy gamma ray emitting sources such as thorium, uranium, plutonium and other actinides. The software discussed here enables automatic creation of an MCNP input data file based on computed tomography (CT) scanning data. The utility was first tested for low- and medium-energy actinide emitters on Livermore phantoms, the mannequins generally used for lung counting, in order to compare the results of simulation and measurement. From these results, the utility's ability to study uncertainties in in vivo calibration were investigated. Calculations and comparison with the experimental data are presented and discussed in this paper.

The use of a Monte Carlo code for the analysis and interpretation of whole body counting measurements is described. The sources of error are analysed and commented to show how a counting geometry can be improved by improving accuracy and precision in a measurement. The effects of body size, contamination distribution and counting geometry are also parameters which can be easily used to improve the quality of a body burden assessment. The optimisation of the detector (position, shielding, shape and size) is also commented on the basis of calculations in the photon energy range usually encountered in routine measurements. The results obtained from these simulations are confirmed by experimental results.

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In vivo monitoring of low-energy X-and -tray emitters has always been a difficult task, primarily because of lack of accuracy and the high detection limits of classical techniques. Various types of PIN diodes (diodes with a large intrinsic zone) were tested in the Radiation Protection Department of the Studie Centrum voor Kernenergie, Centre d'6tude de l'Energie Nucleaire (Mol, Belgium) in the measurement of radioactive body burden by direct methods. Current research is oriented toward the use of room-temperature diodes for the detection of low-energy photons escaping the body. In this paper, a new counting technique that involves a portable jacket containing the diodes is described. The system uses silicon diodes and is used out of a shielding room in order to be near the contamination. With this method rapid analysis and long counting times are possible, stress is reduced, and medical treatment can be optimized. CdZnTe detectors were also evaluated for this measurement Figure 1. Although manipulation of this device is difficult, especially when radioactive charges must be changed, its advantages are imp6rtant: It has a true (corrected) skeleton; the cartilage is represented (with leather); it contains 40K homogeneously distributed; and it is possible to simulate all types of radioactive charge distribution. The absorption parameters of this phantom were controlled by loading it with different charges of 241Am homogeneously distributed and by measuring the phantom Comparison of the various curves corresponding to different energy zones indicates the importance of diffusion of the photons in tissues of the body. This is why it is necessary to consider a broad range of energy and why the resolution of the diode is of secondary importance. The bias voltages were chosen to reach full depletion of the junctions (125 and 10OV, respectively, for silicon and CZT instead of the recommended 100 and 60V). This technique allows a higher efficiency and a stable response and does not affect the resolution or the lifetime of the semiconductor even if an increase of the leakage current intensity is observed.