Development of gamma-ray detector sensitive to source directions using GAGG(Ce) scintillators and MPPCs

We have developed a simpler, smaller, and thus less expensive gamma-ray detector that can roughly determine the incident direction of a radiation source with moderate angular resolution, aiming for personal use beyond that afforded by conventional survey meters. The detector consists of six GAGG(Ce) scintillators with dimensions of 20 × 20 × 6 mm
³
on each face of a 3-cm cubic lead block. Signals from each scintillator are read by a 3 × 3 mm
²
Hamamatsu MPPC. We then applied χ
²
fit to the observed count number set in order to determine the incident direction and set our angular accuracy goal of 22.5°. Through simulation, we injected 662 keV gamma rays uniformly from in front of the detector. We found that the R
₉₀
is distributed from 6.0° to 18.3° in all 980 directions for one-minute exposure to a
¹³⁷
Cs source that gives 0.15 μSv/h. Furthermore, our detector achieved the targeted value under BG intensity of 0.25 μSv/h in the experiment.