Gamma-ray transmission evaluation using imaging plate designed for X-ray radiography

A commercial imaging plate (IP) designed for X-rays and a cesium-137 radiation exposure device were employed to evaluate gamma-ray transmission over the wide surface area of a specimen. A thin copper sheet was used as an intensifying material to enhance the sensitivity of the IP to gamma rays. The response of the copper-covered IP to the transmitted gamma ray was expressed as a two-dimensional gray-tone digital image. The relationship was experimentally determined between the transmission of copper plates with different thickness and corresponding gray values on the digital image. The gray value of the specimen was compared with the one of the copper plate exposed simultaneously on the same image to evaluate gamma-ray transmission. A two-dimensional array of stainless steel balls was fabricated as an example specimen with non-uniform thickness and many voids and its transmission was evaluated as a test. The transmission evaluated from the image agreed well with the one calculated using PHITS and the one measured with an ion chamber. The image of a thick concrete brick showed that a difference in gray values appeared between the center and edge parts. Spread of Compton scattering gamma rays was found to affect the image of a thick specimen.