Resolving pile up with a real-time processor for delay line detectors

We report on the upgrade of a position-sensitive neutron detector for the D17 neutron reflectometer at the ILL Grenoble. The maximum count rate of this instrument has been increased to 420 kHz without sacrifice of spatial resolution. Using a multi-hit Time-to-Digital Converter and a RISC VME processor, we have implemented a real-time position reconstruction algorithm which improves the detector efficiency by recovering piled-up neutrons. The analysis relies on software cathode time checksums, thus avoiding position-dependent inefficiencies and reconstruction errors.