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Jungwon Precision Ind. Co., Ltd. has recently developed precise carbon-interspaced antiscatter grids by adopting the sawing process in order to employ them to digital radiographic (DR) systems. Twelve grid samples of strip densities ranging from 40 to 85 lines/cm at a fixed grid ratio of 5:1 and of grid ratios from 5:1 to 10:1 at a fixed strip density of 80 lines/cm were prepared and their physical characteristics were examined under a well-controlled test condition with the IEC standard fixture, in terms of the transmission of primary radiation, the transmission of scattered radiation, the transmission of total radiation, the contrast improvement factor, and the Bucky factor. We expect that these experimental results will be useful for the selection of antiscatter grids in the applications of DR imaging as well as for the improvement of grid design.

As a continuation of our digital radiographic sensor R&D, we have developed a digital gamma imaging system based upon the cadmium-telluride (CdTe) photoconductor for the applications of industrial gamma-imaging. The imaging system consists of a commercially-available CMOS pixel array of a 100 x 100 m 2 pixel size and a 5.4 x 151.0 mm 2 active area, coupled with a 750-m-thick CdTe photoconductor, and a collimated selenium ( 75 Se) radioisotope of an about 2.3 x 10 12 Bq activity and a physical size of 3.0 mm in diameter. In this study, we, for the first time, succeeded in obtaining useful gamma images of several test phantoms with the 75 Se radioisotope from the imaging system and evaluated its imaging performance in terms of the line spread function (LSF), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). For comparison, we also tested its X-ray imaging performance with a microfocus X-ray tube of an about 5 m focal spot size at an operation condition of 90 kV p and 100 A. According to our test results, the designed imaging system seems to be promising for our ongoing application of nondestructive testings, provided that the effective source size of the 75 Se radioisotope can be further limited.