Characterization of a terbium activated gadolinium oxysulfide plastic optical fibre sensor in photons and protons

A characterization study was carried out to determine if a novel, millimeter sized Terbium-activated Gadolinium Oxysulfide optical fibre detector has potential for future use in proton dosimetry. Preliminary studies employed a Theratronics Theratron 780C Cobalt-60 unit and were used to determine nominal dose response, field size response and Čerenkov contributions in 1.25-MeV gamma radiation. More extensive testing was done using 74 MeV-protons produced in the TRIUMF 500-MeV cyclotron facility examining raw Bragg peak, spread out Bragg peak, dose response, and Čerenkov signal. The detector was low-cost and easily assembled; it showed excellent sensitivity, signal to noise ratio, and reproducibility. Quenching at high linear energy transfer was severe. Additional investigations are needed to further explore Čerenkov-only depth-dose curves, signal detection at the extreme distal end of the Bragg peak, and possible sensitivity to neutrons.