Performance of a Digital Gamma-Imaging System Based Upon CdTe-CMOS Sensor and $^{75}$ Se Source for Nondestructive Testing

As a continuation of our digital radiographic sensor R&D, we have developed a digital gamma-imaging system based upon the commercially-available CdTe-CMOS sensor (AJAT, SCAN1000) and the ⁷⁵Se gamma source (MDS, Gamma Mat^@ SE) for our ongoing application of nondestructive testing. Here the sensor has a 750-mum-thick CdTe photoconductor as an efficient radiation converter and a CMOS pixel array having 100times100 mum² pixel size and 5.41times51.0 mm² active area, bump-bonded to the photoconductor for signal readout. The source has about 62.8 Ci activity and a physical size of 3.0 mm in diameter. For the first time in this project, we have succeeded in obtaining useful gamma images from the imaging system and evaluated the imaging performance in terms of the resolving power, 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 evaluated the image quality by using a microfocus X-ray source (Hamamatsu, L9121-01) having a focal spot size of about 5 mum.