Study on gamma-ray imaging with an image-intensifer and a cooled CCD camera

摘要

The purpose of this study is visualization of concealed light elements materials in metallic environments using a cooled CCD camera with an image intensifier. In this study, gamma-rays were used for visualization. As a gamma-ray source, radio-isotopes such as ~57Co, ~137Cs were used. Gamma-rays penetrate through sample materials and are firstly enhanced by an image intensifier and then detected by a cooled CCD camera. Materials such as explosives or organic matters were observed through various metal plates. The thickness of metal plates is 8mm. Images taken by a cooled CCD camera were accumulated for up to 20miniutes depending on the penetration intensity of gamma rays and gamma-ray energy, and then digitized with 16bit quantization. By this system, enlarged images of small parts of a sample can be observed. By using ~57Co and ~133Ba as a gamma-ray source, images of light elements materials were observed rather clearly but image contrast becomes low when using ~137Cs. This is due to the reduction of gamma-ray absorption coefficient and the reduction of efficiency of the image intensifier for ~137Cs. Using these gamma-ray images, principal component analysis (PCA) was applied. By PCA, the part which includes materials and the part which does not include materials in the sample is clearly separated. In addition, the distortion correction method was also discussed since images obtained by the system have geometrical distortion.