Fast timing with BGO (and other scintillators) on digital silicon photomultipliers for Prompt Gamma Imaging

Particle therapy is supposed to be an advanced treatment modality compared to conventional radiotherapy because of the well-defined range of the ions. Prompt gamma rays, produced in nuclear reactions between ion and nuclei, can be utilized for real-time range verification to exploit the full potential of particle therapy. Several devices have been investigated in the field of Prompt Gamma Imaging (PGI), like Slit and Compton Cameras. The latter need very high detection efficiency as well as good time and energy resolution, requiring a versatile scintillation detector. In Positron Emission Tomography (PET), LSO and LYSO are known for their good time resolution, while the lower cost alternative BGO shows worse performance. In PGI however, where gamma rays have energies up to 10 MeV, the light output of a scintillator is up to 20 times larger compared to PET. This reduces the statistical contribution of the time resolution, which is the dominant part in case of BGO. Thus, BGO could be a reasonable alternative to LSO/LYSO for applications in PGI. Hence, experiments at the ELBE accelerator at HZDR (Germany) were performed using digital silicon photomultiplier (dSiPM) from Philips with monolithic BGO and LYSO crystals, and for completeness with GAGG, CeBr
₃
, CsI, CaF
₂
, and GSO. The time resolution of BGO compared to the other scintillators will be presented for a wide range of trigger- and validation levels as well as validation lengths of the dSiPM. Timing resolutions below 220 ps are obtained for BGO, while LYSO and CeBr
₃
achieve about 170 ps.