Digital coincidence counting – initial results

Digital coincidence counting for radionuclide standardization

“…The NPL and the ANSTO developed a dedicated PC-based DCC data capture hardware system [8,9] which incorporates two independent 12-bit flash ADCs utilizing a common 20 MHz CMOS sampling clock. A real-time data compression filter (figure 3) operates independently on each of the input data streams and retains only sampled voltages above the defined threshold levels (thus storing the pulse shapes) along with a 40-bit time-stamp (50 ns resolution) representing the number ), which handles the processing, data conversion and provides a PCI V2.1 compliant 32-bit, 33 MHz digital interface with the host PC capable of a maximum of 132 Mbytes s −1 data transfer.…”

“…The output data are streamed to disk in real time after concatenation to a file header (containing information such as the start time and date of the measurement, the ADC clock frequency and the threshold levels for each channel). The exact data format for a given pulse record [10] and further details on the data collection hardware may be found elsewhere [8,9,11].…”

“…All of these digital systems are limited in the count rates that can actually be digitized (typically relating to a source activity of about 30 kBq), due to the high data throughput rates and nuances of the data collection hardware. In order to test fully the behaviour of each suite of analysis software, a data simulation model has been developed [8], which mimics the operation of the NPL/ANSTO DCC data collection hardware system at higher count rates than are presently achievable. The data sets generated by the other digital systems are mimicked within the data conversion routines, and are used for subsequent analysis by the other participating NMIs for a direct comparison of the calculated activity of the radionuclides under study.…”