Hardware development for imaging

Characterization of scintillation detectors and development of front-end
electronics

Scintillators are widely used and well known in the field of gamma detection. There is a large community dealing with their characterization, matching them with optimized photo detectors and discussing possible applications in order to find the best scintillator and photo detector combination for a given task. The development of larger and more effective SiPMs requires an adapted front-end electronics concept for optimized performance. Several concepts for in-vivo range verifications are currently being discussed, each of which has very specific requirements on the detection system:

• Collimated systems as the slit camera focus on counting the prompt gamma rays behind passive collimators; hence, the requirements on a gamma detector are limited to an excellent spatial resolution and good count rate capabilities.
• The Compton camera concept is another promising possibility, although it is rather complex; the detectors have to provide good spatial and time resolution as well as excellent energy resolution for reconstructing the origin of the prompt gamma rays.
• The Prompt Gamma Timing method utilizes the particle transit time in tissue to extract its range. In this case, the timing characteristics of the detection system are most important, while energy resolution as well as spatial resolution is dispensable.
• PT-PET aims at the coincident detection of annihilation gammas, originating from positrons, whose emitters have been produced during particle irradiation. While the gamma energy is fixed to 511 keV, time resolution is an important parameter, as well as the spatial resolution of the system.

For each concept, the detection system must meet special requirements regarding energy, time, and spatial resolution. Nonetheless, the prerequisites remain the same: the gamma energy region (2 to 10 MeV for prompt gamma emissions, 511 keV for PET application), high counting rates and the stability in strong background radiation fields.

The characterization of scintillators is done with commercial electronics at several experimental sides: The ELBE – Center for High-Power Radiation Sources for timing measurements at energies of bremsstrahlung up to 16 MeV, the 3MV Tandetron facility for mono energetic 4.4 MeV photons stemming from an ¹⁵N (p,αγ) ¹²C resonancereaction and the Proton facility at the OncoRay for measurements in a clinical environment.

For optimized spacial resolution, systems using SiPMs are an alternative to PMT based detectors. The customized preamplifier modules were designed with a low noise linear voltage converter for noise suppression and voltage supply. They incorporate two separate amplification paths for energy and timing measurements. The energy signal preamplifier was developed for the use with ADCs and QDCs
without an overshoot or baseline offset.