Optimization of the backing material of a low frequency PVDF detector for ion beam monitoring during small animal proton irradiation

This study investigates the use of PVDF sensors for the detection of low pressure kHz thermoacoustic signals, emanating from pulsed proton beams during small animal irradiation. In particular, the impact of the backing material and detector geometry on the measured signal amplitude and accuracy of time-of-flight estimations is assessed. A simulation model, including FLUKA Monte Carlo simulations of the proton dose, pressure propagation using k-Wave, modeling the backing geometry and a Mason model of the PVDF electroacoustic response is proposed. Thereafter, suitable backing materials are investigated by varying the backing density, the speed of sound and the detector geometry. Tungsten is found to be a good candidate to improve the sensor sensitivity, while maintaining accurate localization of the maximum of the proton dose, i.e., Bragg peak localized with an error lower than 5 % for the considered scenarios. Tungsten backing as thin as 2.5 mm allows to improve the sensitivity of the detector by a factor 4 compared to 10 mm epoxy backing.