Design of a Linear Detector Array Unit for High Energy X-ray Helical Computed Tomography and Linear Scanner

Abstract

A linear detector array unit (LDAU) was proposed and designed for the high energy X-ray 2-D and 3-D imaging systems for industrial non-destructive test. Specially for 3-D imaging, a helical CT with a 15 MeV linear accelerator and a curved detector is proposed. The arc-shape detector can be formed by many LDAUs all of which are arranged to face the focal spot when the source-to-detector distance is fixed depending on the application. An LDAU is composed of 10 modules and each module has 48 channels of CdWO4 (CWO) blocks and Si PIN photodiodes with 0.4 mm pitch. This modular design was made for easy manufacturing and maintenance. Through the Monte Carlo simulation, the CWO detector thickness of 17 mm was optimally determined. The silicon PIN photodiodes were designed as 48 channel arrays and fabricated with NTD (neutron transmutation doping) wafers of high resistivity and showed excellent leakage current properties below 1 nA at 10 V reverse bias. To minimize the low-voltage breakdown, the edges of the active layer and the guard ring were designed as a curved shape. The data acquisition system was also designed and fabricated as three independent functional boards; a sensor board, a capture board and a communication board to a PC. This paper describes the design of the detectors (CWO blocks and Si PIN photodiodes) and the 3-board data acquisition system with their simulation results.