Proton beam monitoring through water scintillation in radiobiology experiments

Non-invasive methods based on the detection of secondary particles generated in the irradiated medium are being investigated to monitor ion beams without disturbing the beam. This study investigates the use of water scintillation as a beam monitoring tool, taking into account the challenges posed by the radiobiology experiment constraints. An experimental setup has been designed to measure the depth deposited energy profile produced by protons of (67.5 ± 0.4) MeV entering a water tank, through the water scintillation detected with a photomultiplier. The beam current during the experiment was around 100 pA, and beam intensity fluctuations were monitored using a parallel plate ionization chamber and a Faraday cup. The experiment was repeated with a second ionization chamber as a reference detector placed inside the water tank, and simulated with the GATE Monte Carlo code. The position of the Bragg peak, measured with the water scintillation, shows significant agreement (deviation of 0.5 mm) with the positions obtained from the ionization chamber and the Monte Carlo simulation within a submillimeter uncertainty. The ionization quenching effect was also observed and corrected using the Birks and Chou models. A new value of the key parameter for these models (k $·$ B = (8.0 ± 4.0) × 10⁻³ g/MeV.cm²) has been determined for water, which is in good agreement with the data available in the literature for organic scintillators. This study demonstrated the feasibility of using water scintillation measured with a collimated photomultiplier as a tool for monitoring the depth deposited energy profile in water.