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Characterisation and functional test of the full readout chain of a microdosimeter using scintillating plastic optical fibres
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Resumo(s)
Instruments with a high spatial resolution are necessary to measure dosimetric quantities at a
cellular level in order to have a better delineation of treatment plans in radiotherapy. The work
here described is within a project aiming to develop a new detector capable of measuring real time absorbed dose with sub-millimetre resolution. The device is constructed using juxtaposed
scintillating plastic optical fibres (SPOF) readout by a multi-anode photomultiplier (MAPMT,
Hamamatsu H8500D) and a data acquisition (DAQ) system. In this thesis a first validation
of the full readout chain is done, going through the characterisation of the different elements
composing this detector.
Using a dedicated test bench SPOFS (Kuraray SCSF-78) of 1 mm and 0.5 mm were optically
characterised, measuring basic properties, such as light yields and attenuation lengths, before
measuring the crosstalk between juxtaposed optical fibres. Methods of analysis were designed
to compare the signal from an isolated and ribbon SPOF.
Next, the MAPMT’s key characteristics were studied using a UV-LED exciting SPOF, to
guide the light to individual MAPMT cells, and a picoammeter as a readout system. Concerning
the assembly of the MAPMT in a detector assembly, the ideal conditions to achieve a light tight
setup were evaluated.
The full readout chain was completed by including a costumed DAQ board. Pulsed LEDs
were firstly used to evaluate main limitations in signal response of the readout chain. Radioactive
sources were then used to test the sensibility to particles (betas, gammas and alphas).
In terms of results, the crosstalk study needs further revision, specially quantifying its value.
The MAPMT’s performance was characterised and validated, whereas the DAQ board observed
saturation and response to particles needs more understanding. However, the integration of
the three elements of the microdosimeter was achieved and could be implemented into a first
prototype.
Descrição
Tese de Mestrado Integrado, Engenharia Física, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Terapia com protões Microdosimetria Fibras ópticas cintilantes de plástico Fotomultiplicador multi-ânodo Placa de aquisição de dados Teses de mestrado - 2022