In this study, a radiation detector based on a silicon
photomultiplier (SiPM) and large Ce-doped Gd-Al-Ga-grant (Ce:GAGG)
scintillator was developed for the gamma spectroscopy observations
of radioactivation from linear accelerators (LINACs). The
calibration of the detector demonstrated a high energy resolution of
15.89% at 122 keV (gamma-ray emission energy of Co-57), 7.04% at
356 keV (gamma-ray emission energy of 133Ba), 6.17% at
511 keV (gamma-ray emission energy of Na-22), and 5.39% at
662 keV (gamma-ray emission energy of Cs-137). These results
indicate that the detector employing a larger Ce:GAGG scintillator
provides a higher detection efficiency while maintaining superior
energy resolution compared to conventional radiation detectors that
use smaller Ce:GAGG scintillators. Furthermore, the energy spectrum
measurement of the LINAC revealed detection of neutron and gamma
peaks of W-187 and Mn-56, as well as annihilation peaks. Although
the energy resolution of the detector was inferior compared to an
HPGe detector, it was able to measure similar energy
peaks. Therefore, the radiation detector developed in this study,
which is characterized by its low cost, decent energy resolution,
and high detection efficiency, may be useful for obtaining radiation
measurements during the disposal of LINACs.