MODULAR DATA-ACQUISITION SYSTEM BASED ON TRANSPUTER TECHNOLOGY FOR BI-DIMENSIONAL TIME COINCIDENCE COUNTING

We describe the rationale and the test of a modular Data AcQuisition s ystem (DAQ) for bi-dimensional (X-Y) digital imaging, based on a 16 ch annel Time-to-Digital Converter (TDC) NIM module connected to a specia lly designed TRAnsputer Module (TRAM). TDC time resolution is 12.5 ns (LSB) with a 40 MHz clock, time range is 3.3 s (28 bits), for a maximu m rate of 500 kHz/channel guaranteed. The TDC + TRAM pair is the basic unit that can be scaled in modules of 8X + 8Y channels to meet the us er's requirement for a larger number of X-Y channels to be considered simultaneously. TDC directly accesses the large RAM memory (32 Mbytes) of the INMOS T805 (20 MHz) transputer on the TRAM board. Each transpu ter in the modular system is a node of a ring network, whose root tran sputer node is hosted in a i386-based personal computer. After real-ti me data acquisition, a parallel reconstruction algorithm resolves time coincidences. Laboratory tests give a reconstruction time of 6.2 s fo r 1.28 10(5) events on 16 X + 16 Y channels (2 TDC + 2 TRAM), obtained in 1 s with a fluence of 5 X 10(4) events/mm2 (typically used in radi ological imaging) on an area of 1.6 X 1.6 MM2.