Development of a Compton camera for online range monitoring of laser-accelerated proton beams via prompt-gamma detection

Presently large efforts are conducted in Munich towards the development of proton beams for bio-medical applications, generated via the technique of particle acceleration from high-power, short-pulse lasers. we aim at developing a reliable and accurate online range monitoring technique, based on the position-sensitive detection of prompt rays emitted from nuclear reactions between the proton beam and the biological sample. For this purpose, we develop a Compton camera, designed to be able to track not only the Compton scattering of the primary photon, but also to detect the secondary Compton electron, thus reducing the Compton cone to an arc segment and by this increasing the source reconstruction efficiency. The design specifications of the Garching Compton camera have been determined in extensive simulations using the MEGAlib simulation/reconstruction software package. The design of our Compton camera system is based on a LaBr₃(Ce) scintillation crystal acting as absorber (50*50*30 mm³), preceded by a stack of 6 double-sided silicon strip detectors (DSSSDs) as scatterers. The scintillation material LaBr₃ is favourable in view of its unprecedented fast timing properties, while simultaneously exhibiting very good energy resolution. In order to achieve optimum position resolution for the absorbed photon, the scintillation crystal is read out by a segmented multi-anode photomultiplier (PMT, Hamamatsu H9500C) with 16*16 pixels of 3*3 mm²