Development of a novel radiation monitoring system using a variable lofthole collimator

This study aims to develop a variable lofthole (VL) collimator-based gamma camera with a zoom function for detecting radioactive materials in radiation disaster situations. The VL collimator comprises seven layers, each forming a square hole with four tungsten (W) plates. Each layer of a W plate was controlled using four spur gears: external, internal, and rack gears. The VL collimator had a symmetrical structure. The detector was composed of a combination of a gadolinium aluminum gallium garnet scintillator doped with cerium (Ce:GAGG) and a silicon photomultiplier in the form of a two-dimensional array. In addition, a linear actuator was designed to enable precise forward and backward driving of the detector along with driving of the collimator to realize a magnification suitable for this purpose. The experimental results demonstrated that the full width at half maximum (FWHM) for the square hole size of 10 × 10 mm² to 2 × 2 mm² of the VL collimator at an acceptance angle of 45 ° decreased from 58.5 to 17.5 %, respectively. When the reception angle was reduced from 45 ° to 16 ° in a VL collimator with a square hole size of 3 × 3 mm², the magnification increased by a factor of approximately 2.6. As the magnification increased, the spatial resolution improved, and it was confirmed that the two sources were well-distinguished. The results showed that the VL collimator-based gamma camera system designed in this study can be used to image radioactive materials with high sensitivity and resolution in radiation-related disaster situations.