Gamma ray detecting device using dislocation-free crystal

This patent describes a γ-ray detector. It comprises: a dislocation-free single crystal having an input surface and a transmission surface at opposite ends thereof; an active shield surrounding the crystal and functioning as an anticoincidence counter; and γ-ray detector means disposed adjacent the transmission surface of the crystal for receiving and detecting γ-rays of a predetermined wavelength incident on the input surface of the crystal at a specific Bragg angle and transmitted through the crystal