Florbela Rego

Response of plastic scintillators to low-energy photons

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.

What are the 50 cent Euro coins made of

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.

Scintillating optical fiber dosimetry with photodiode readout

Plastics are a great material to be used as a dosimeter. Their radio-properties are similar to water, so correction factors to convert the measured dose into dose in water are small. Traditionally the light from plastic dosimeters has been measured using PMT’s. An effective alternative is provided by photodiodes, which have broader wavelength sensitivity, allowing for the use of lower wavelength photons.

Deteção da radiação térmica emitida por um filamento de tungstênio aquecido

A demonstracao da lei de Stefan-Boltzmann recorrendo a uma lâmpada de incandescencia como corpo negro ja se tornou uma experiencia classica. Neste artigo exploramos a utilizacao de fotodiodos de baixo custo como fotodetetores neste tipo de experiencia e apresentamos uma discussao dos resultados obtidos com base na distribuicao espetral de Planck.

Plastic scintillator dosimetry in radiology applications

Plastics have attractive characteristics that can be exploit in dosimetry. Nevertheless their application with low-energy photon beam is still limited. We aim to a better understanding of their capabilities at the radiology regime. A study of the characteristics of a polystyrene scintillator dosimeter, coupled to a WLS fiber is made in this work. The energy dependence for this detector is extracted for photon beams between 20 and 100 kVp and additional filtrations of 0.5, 1 and 4 mm of Al.

Small dimension plastic dosimeter in high dose rate brachytherapy with 192 Ir source

Dosimeters made of scintillating optical fibers have interesting properties and due to its small dimensions can found a field of application in brachytherapy. In this work we exploit the properties of such a dosimeter when irradiated with a clinical 192Ir radioactive source. Furthermore, we compare its response to the responses of an ionization chamber and a MOSFET dosimeter irradiated under the same conditions.