1. Digital signal processing for a thermal neutron detector using ZnS(Ag):6LiF scintillating layers read out with WLS fibers and SiPMs
J.-B. Mosset, A. Stoykov, U. Greuter, M. Hildebrandt, N. Schlumpf
Summary
The poster describes the principle of the signal processing system (SPS) for the new thermal neutron detector currently under development for upgrading the POLDI instrument, a strain scanning diffractometer installed at the Swiss neutron spallation source (SINQ) at PSI. The performance of 3 digital filters are presented.
Principle of the signal processing system (SPS)
Photon counting approach.
Density in time of photons (and SiPM dark counts) is sampled at a period of 400ns.
Once sampled, the signal is digitally filtered.

2. Digital filters under evaluation
Digital filters under evaluation (xi = filter input, zi = filter output)
The evaluation is based on real data consisting of temporal sequencies of the digital pulses produced by the discriminator (SD pulses) during the 80µs following the neutron captures.
a) Moving sum zi = zi + xi – xi-M
b) Moving sum after differentiation yi = xi – xi-M zi = zi + yi – yi-M
c) Discret-time implementation of a CR-RC4 analog filter
Conditions:
Probability of multiple triggers < 10-3
Background rate < 10-3 Hz