Development of All Directional Gamma-ray Imager with Fine Bar-type Scintillators

We have been developed a stacked scintillator detector based on Compton scattering gamma camera in order to detect the incident direction of radiations emitted from released radioactive material rapidly. This detector supports workers and evacuating citizens to protect from radiation hazards in the case of severe accident of nuclear power station such as of Fukushima Dai-ichi accident. An important performance required for this purpose is to operate in high dose rate environment. In order to reduce chance coincidence, our detector was composed of fine scintillator bars which ends were connected to photon sensors and each scintillator bar worked individually. The symmetric geometry of this detector provided a rapid detection sensitive in all directions. We stacked 64 fine scintillator bars and the performance was evaluated experimentally. An experimental demonstration was successfully made to find the radioactive sources (
¹³⁷
Cs). It was confirmed that this detector was sensitive for all directions and the angular resolution was 60 degree for 662keV gamma-ray. The upper limit of dose rate was estimated by Monte-Carlo simulations. It was 10 mSv/h to reconstruct corresponding image for a point source of
¹³⁷
Cs. This detector was applicable for the outdoors use in the severe accidents of nuclear power stations.