Evaluation of a method for time-of-flight, wavelength and neutron flight path calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors

Abstract Accurate conversion of neutron time-of-flight (TOF) to wavelength is fundamental importance scattering measurements in order ensure the accuracy instruments and experimental results. Equally important these determination uncertainties, with appropriate precision. Especially cases where are highly configurable, absolute after any change must always be performed (e.g. detector position). Inspired by manner which spectrometers determine wavelength, we evaluate for first time, author's knowledge, a commonly used method converting TOF measuring flight path length from source neutrons monitor proceed analytically calculate uncertainty contributions that limit precision conversion. The was evaluated at V20 test beamline Helmholtz Zentrum Berlin (HZB), emulating ESS long pulse 2.86 ms 14 Hz repetition rate, using mini-chopper operated 140 two portable beam monitors (BMs), as well accompanied data acquisition infrastructure. created well-defined pulses BM placed positions, enabling average each determined. setup resulted positions δλ mean / λ ∼1.8% > 4 Å. With use thinner monitor, ∼1% can reached modest increase distance between reference below 0.5% achieved. Further improvements possible smaller chopper disc openings higher rotational speed chopper. requires only doesn't necessitate crystals or complex fitting sigmoid functions multiple free variables, could constitute suitable addition imaging, diffraction, reflectometers small angle instruments, spallation sources, do not normally utilise fast choppers.