A fast neutron time-of-flight and scattering angle measuring system with online flight time correction

The paper describes a microprocessor controlled VMEbus system for neutron scattering experiments at the new Berlin Experimental Reactor BER II. The system measures the distribution of neutron time-of-flights by spatially distributed detectors (400 single detectors or a multi-detector array with 4096 elements) and generates a two-dimensional histogram with 4 K time channels and 4 K detector position channels in a 32 MB memory. Several outstanding features are described in detail: 1) Online time-of-flight correction compensates different lengths of neutron flight paths, in order to obtain undistorted spectra if, e.g., a planar detector array is used. 2) The system is designed for very fast processing of the events detected, to allow high neutron counting rates of up to 500,000 neutrons/s on average and up to 2×10⁶ neutrons/s as a peak rate. 3) To provide a maximum of flexibility for the user, the operation of the system is based on pre-calculated tables and parameters which allow a wide variety of system configurations to satisfy very different requirements of the experiments