A PCI DAQ board for MWPC detectors with high-rate 2D delay line position readout

For high rate thermal neutron (and e.g. also synchrotron radiation) detection a PCI data acquisition (DAQ) board for readout of two-dimensional position-sensitive multi-wire proportional chamber (MWPC) detectors with delay line position encoding was developed, and a first series of boards was produced and tested. The MWPC board comprises a deadtime-less 8-channel multihit TDC chip of the F1 type with ∼120 ps LSB, a 40 MHz flash ADC, a FPGA, a FIFO, a 0.9 GFLOP DSP chip TMS320C6711 and a 256 MB histogram memory. For position encoding a position-independent start and four position-dependent stop signals are recorded from the MWPC anode and from either end of X and Y delay lines connected to the MWPC cathodes, respectively. Time-of-flight (TOF) can be measured with reference to a pulsed beam or chopper signal either with ⩾25 ns bin size for TOF ranges of up to ∼420 ms or alternatively with ∼120 ps LSB for ranges ⩽16 ms. The pulse height of the MWPC anode signal is digitized in the flash ADC for neutron-gamma and background discrimination. Hardware event filtering in the FPGA allows event rates up to 1 Mevents/s by disentangling of two events occurring within the delay line time length of e.g. 250 ns. Whilst list mode data are recorded with full rate and full resolution on the host PC disk, 1D–3D histograms can be accumulated online in the on-board HM for a fraction of the data and with reduced resolution.