Study of the photon rejection of the ALPIDE pixel detector for medical applications

The ALPIDE silicon pixel detector, designed for the upgrade of the ALICE Inner Tracking System at the CERN LHC, is potentially well suited also for usage in other fields, as for medical applications. In particular, it could provide excellent capabilities as detecting probe for radioguided surgery in oncology, in association to positron-emitting radiotracers. In this respect, to quantify the expected performance it is crucial to measure the sensitivity to low-energy photons, which constitute the main background for revealing the positron radiation. Due to its thin epitaxial sensitive layer, the ALPIDE is expected to be almost insensitive to photons. A measurement of the ALPIDE efficiency for the detection of 662 keV photons, emitted by a Cs-137 radioactive source, is reported in this paper. A value of 0.089%, with a relative uncertainty of 20%, was obtained, granting an excellent rejection of low-energy photons compared to other proposed devices.