A γ-ray scanner includes a Solid-State Single-Photon Detector (“SSSPD”) and a γ-ray source, which may be a radioisotope such as Americium oxide (Am-241) that may not require certification since it has a low intensity that is safe even over extended periods of exposure to a human body. The γ-ray scanner may be used for monitoring a fixed object such as a pipe and includes an imaging assembly having a stationary annular gantry surrounding the pipe and an armature that fixedly supports the γ-source and the detector in mutual opposed alignment, so that they are constrained to move together. The armature rides around an inside periphery of the gantry, while the armature or the gantry moves laterally in a direction parallel to a rotation axis of the armature so as to move the γ-ray beam around and along the pipe.