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 system (DAQ) for bi-dimensional (X-Y) digital imaging, based on a 16 channel Time-to-Digital Converter (TDC) NIM module connected to a specially 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 maximum 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 user'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 transputer in the modular system is a node of a ring network, whose root transputer node is hosted in a i386-based personal computer. After real-time data acquisition, a parallel reconstruction algorithm resolves time coincidences. Laboratory tests give a reconstruction time of 6.2 s for 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 radiological imaging) on an area of 1.6 X 1.6 MM2.