[en] Positron Emission Tomography (PET) is a medical nuclear imaging technique in which the patient is injected with an organic compound, biochemically active, labelled with a positron emitting isotope. Upon emission, the positron travels a few millimetres before it annihilates with a nearby electron emitting two 511 keV photons back-to-back. From the point of view of instrumentation, PET requires the detection of those annihilation photons in coincidence, with high efficiency (around 80%), position resolution of the order of a few millimetres, good time resolution (better than 5 ns) and high count rate capability (100,000 to 1,000,000 cps/s/cm² on the detection area). In the present work, the proposal of a liquid xenon detector for PET is presented and discussed. On the basis of experimental results obtained with a prototype chamber, together with computations, one expects an azimuthal space resolution of about 1 mm, time resolution of about 1.5 ns and detection efficiency of 75%. Conversely to what happens with the present tomographs, based on used scintillating crystals, such as NaI(Tl) and BGO, the availability of position resolution along the radial direction will allow for the correction of the parallax errors, improving the position accuracy for peripheral points of the field-of-view of the tomograph

[en] The process of food preservation by ionising radiation is an alternative, or a complement, to the traditional methods of heating, refrigerating, freezing or using chemical additives. The study and development of this technique has started on the beginning of the fifties but it is based on the radiation killing effect on micro-organisms discovered by the end of last century. Foodstuffs are treated in appropriate plants: isotopic facilities (gamma radiation) and accelerated electron beams produced by machines called accelerators. The FAO and WHO in close cooperation with the IAEA have played an important role on the development of the process and on the increment of the industrial application of food irradiation. Over the world there are about 37 countries trading foods treated by ionising radiation. However, governments have been slow to clear the utilization of this process. The main reason of this attitude is in general due to the fact that the advantages of the technique are not clearly understood. Therefore, the dissemination of the information could on one hand clarify who has to take decisions and on the other hand support the choice of those foods by the consumers. This is the unique way to dynamize the application of this process

[en] The basic aspects of radiation protection in nuclear magnetic resonance are briefly reviewed, from the physics parameters to the biological effects. Counter-indications for this technique are discussed

[en] This study was carried out to evaluate the feasibility of using commercial PIN diodes BPW-34, SFH-205, SFH-206 and XRA-5 for x-ray spectrometry. The main characteristics are: active area between 0.073 and 0.25 cm², thickness of the entrance window of 57mg/cm², and junction capacitance of 72 pF at 30 V. The photodiodes were reverse biased and connected to a charge sensitive pre-amplifier, followed by a pulse shaping amplifier and multichannel pulse analyser. Standard radiation sources used in these experiments were Am-241, Cd-109, Co-57 and Ba-133. The K x-ray fluorescence peaks of lead and silver were also measured. The results showed that the responses of the photodiodes vary linearly with the radiation energy and that the energy resolution (FWHM) varied between 1.9 keV and 4.1 keV, for peaks ranging from 11.9 keV to 59 keV, respectively. The photopeak efficiency, on the other hand, ranged from 0.003 to 0.53%. The BPW-34 showed the best energy resolution among the photodiodes tested in this work. (author)

[en] This work aims at the study of the thermal stability if GR-200 compared to the classical TLD-100, taken as a reference. The thermal stability was studied by storing samples of both materials, both irradiated and unirradiated, in laboratory controlled conditions at 40 and 70 degrees Celsius for storage periods that varied from 6 hours to 24 days. These two temperatures were considered as representative of the temperature endured in environmental exposures. All curves were analysed using simplified and computerised methods. Computerised methods perform the deconvolution of the glow curve on its individual peaks, so that the evolution of each peak could be followed. In this way the temperature induced effects on filled and empty traps (irradiated and unirradiated detectors) could be followed. The results show that GR-200 is far more stable than TLD-100 for the two temperatures studied. They also show that the migration and aggregation of the impurities based defects that alter the structure of the trap system are the main cause of the observed sensitivity changes. Thermal fading, understood as the the spontaneous release of the trapped charges, does not influence the behavior of the main peaks in both materials (author)

[en] Dose measurements for the narrow photon beams used in radiosurgery are complicated by the lack of electron equilibrium which is a requirement namely for ionometric methods. To overcome this difficulty the use of different dosimetric supports is strongly recommended in order to appreciate the influence of each type of detector. Monte Carlo simulation is another kind of tool to assess the details of the energy deposition phenomena in such narrow photon beams. In this study output factors and depth dose calculated by the Monte Carlo MCNP-4C code are presented and compared with experimental data measured with a diode, a Markus chamber, a 0.125 cc thimble chamber and a Pinpoint chamber. Simulated energy spectra for narrow beams are also presented in order to compare them with the reference 10 cm x 10 cm beam field size and thus discuss the different contributions of the absorbed energy in water, in each case. A detailed analysis on the photon energy spectra showed a slight decrease on the photon mean energy that can be explained by the increased scattering inside the additional collimators. Calculated and measured depth doses curves are in good agreement for most of the collimators. For the two smallest collimators some differences have been pointed and explained according to the characteristics of the detectors (author)

[en] On a previous work it was observed an increased frequency of chromosomal damage on peripheral blood lymphocytes of miners comparatively with non-miners controls. On this study, that complements previous work, we present a detailed analysis of chromosomal aberrations of one thousand of metaphases, on cases that the miners' lymphocytes exhibit dicentric chromosomal aberration. We saw an over dispersion of damage on cells, and a linear relationship between the total chromosomal damage and working years on mines

[en] The Tagus river receives in its Spanish part discharges from three nuclear power plants (NPP). The closest to the Portuguese border is the Almaraz NPP. The objective of this study is to evaluate the radioactivity levels in the Tagus and Zezere rivers. The main conclusion is that the normal operation of the Almaraz NPP influences the radioactive levels in the Tagus river, mainly in the tritium activity in the water. (author)

[en] The RESTORE Environmental Decision Support System (restoration of radioactive contaminated ecosystems) was developed within the 4th framework programme of the European Commission containing a Geographical Information System combined with radioecological data and models. In order to explore its full potential, different applications of such support system are possible: i) the identification of radioecological sensitive areas, ii) its application to other than radioactive pollution by using the necessary transfer models and parameters e.g. for heavy metals, both for the derivation of remediation strategies, and iii) the combination of information on pollution with epidemiological data on recorded health effects. For this purpose a data base containing spatial and temporal information on radioactive and conventional pollution can be combined with ethnic composition, living habits, education, income, age/sex structure, general sanitary situation, production, import and export overlaid with health data e.g. including congenital malformations, cancer, mental retardation, immunological situation, birth certificates and death certificates. Since a spatial but also temporal resolution of data can be achieved, time trends and spatial trends of a potential impact to human health can be demonstrated. (author)

[en] In order to put into practice the principle of optimization of the radiation protection for the patient in radiodiagnostics, it would be interesting to have an indicator of risk which is better adapted than the effective dose. This last was defined in the publication 60 of the ICRP to reflect the whole body radiological risk for a general reference population, which gathers people of the two sexes and all ages. However, the exposure of the patient in radiodiagnostic is characterized by a partial exposure of the body. Moreover, the frequency of the examinations in radiodiagnostic depends on sex (mammography) and age (examination of scoliosis versus interventional radiology) of the exposed individuals. The objective of this work is to propose sex and age specific risk coefficients of exposure-induced fatal cancer. (author)