Diagnostic radiology typically uses x-ray beams between 25 and 150 kVp. Plastic scintillation detectors (PSDs) are potentially successful candidates as field dosimeters but careful selection of the scintillator is crucial. It has been demonstrated that they can suffer from energy dependence in the low-energy region, an undesirable dosimeter characteristic. This dependence is partially due to the nonlinear light yield of the scintillator to the low-energy electrons set in motion by the photon beam. In this work, PSDs made of PMMA, PVT or polystyrene were studied for the x-ray beam range 25 to 100 kVp. For each kVp data has been acquired for additional aluminium filtrations of 0.5, 1.0, 2.0 and 4.0 mm. Absolute dose in the point of measurement was obtained with an ionization chamber calibrated to dose in water. From the collected data, detector sensitivities were obtained as function of the beam kVp and additional filtration. Using Monte Carlo simulations relative scintillator sensitivities were computed. For some of the scintillators these sensitivities show strong energy-dependence for beam average energy below 35 keV for each additional filtration but fair constancy above. One of the scintillators (BC-404) has smaller energy-dependence at low photon average energy and could be considered a candidate for applications (like mammography) where beam energy has small span.

Radiation is an important aspect of daily life. We interact with radiation from several sources, both natural and manmade, and in fact life on Earth depends on it. Although the general population, and students in particular, can recognize its importance, it is not clear whether they understand its meaning. Bearing these considerations in mind, a study of Portuguese students' knowledge of radiation physics was made and 1246 students from different school levels answered a questionnaire on the subject. In this work we report some of the results obtained.

X-ray fluorescence is a non-destructive technique that allows elemental composition analysis. In this paper we describe a prescription to obtain the elemental composition of homogeneous coins, like 50 cent Euro coins, and how to get the quantitative proportions of each element with the help of Monte Carlo simulation. Undergraduate students can carry out both the laboratory work and the simulation, thus exploiting an analysis technique widely employed in contemporary physics.

High-intensity X-ray beams are usually characterized by their kVp (kilovoltage peak) value and half-value layer (HVL). While the first parameter is reasonably well known (apart from accelerating potential fluctuations), on the second, there is a greater deal of uncertainty. The HVL depends on the used filtration, the effective kVp value and on some of the X-ray tube mechanical features, such as the anode angle. This last parameter is not always provided by the tube manufacturer, so we may question if the HVL dependence on the anode angle can be used to extract information on this angle. We tried to give an answer to this question using two different numerical models and a full Monte Carlo (MC) program to simulate the photon field produced by the X-ray tube for several anode angles. One of the numerical models was developed by the Institute of Physics and Engineering in Medicine and gives X-ray spectra and HVL values for a wide range of kVp values and anode angles. The other model, named SpekCalc, is based on a theoretical work developed by Gavin Poludniowski and Phil Evans. The MC simulation was done using the PENELOPE code for coupled electron-photon transport. Using the computed photon spectra, HVLs were obtained and compared with experimental HVL values obtained with a Philips PW 2184/00 X-ray tube with a 26 • tungsten anode and accelerating potentials in the range of 40-90 kVp. We are now able to show the PENELOPE simulation can deliver the correct anode angle value.

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