Volume 132, Number 2, October 2020
|Number of page(s)||6|
|Published online||22 December 2020|
Parasitic neutron beam monitoring: Proof of concept on gamma monitoring of neutron chopper phases
1 European Spallation Source ESS ERIC- P.O Box 176, SE-221 00 Lund, Sweden
2 Dipartimento di Fisica “G. Occhialini”, Università degli Studi di Milano- Bicocca - Piazza della Scienza 3, 20126 Milano, Italy
Received: 17 April 2020
Accepted: 14 September 2020
Neutron beam monitors are an essential diagnostic component of neutron scattering facilities. They are used to measure neutron flux, calibrating experiments performed on the instruments, allowing measurement of facility performance, understanding of the effect on the neutrons of beam-line components (such as choppers), calibration of detectors and tracking of beam stability. Ideally beam monitors should not perturb the beam. Previous work shows commercial beam monitors attenuate the beam by a few percent in the worst case due to the 1–2 mm thick aluminium entrance and exit windows and the material inside. Parasitic methods of neutron beam diagnostics, where there is no beam monitor directly in the beam, would be preferable. This paper presents the concept of a parasitic method of monitoring the beam which can be used for neutron chopper phasing. This is achieved by placing a gamma detector close to a rotating chopper and measuring a signal proportional to the flux absorbed by the chopper. Neutrons interact with the boron absorber on the chopper disc leading to gamma emission at 480 keV. Detection of these gamma rays is used to determine the chopper phasing and timing. Potentially information on the flux of the beamline can be extracted. Results from a proof of concept implementation show that diagnosis of neutron chopper phases is feasible.
PACS: 28.20.Cz – Neutron scattering / 96.60.tk – X-ray and gamma-ray emission / 29.27.Fh – Beam characteristics
© 2020 The author(s)
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