Characterization of the Multi-Blade 10B-based detector at the CRISP reflectometer at ISIS for neutron reflectometry at ESS

Abstract

The Multi-Blade is a Boron-10-based gaseous thermal neutron detector developed to face the challenge arising in neutron reflectometry at neutron sources. Neutron reflectometers are challenging instruments in terms of instantaneous counting rate and spatial resolution. This detector has been designed according to the requirements given by the reflectometers at the European Spallation Source (ESS) in Sweden. The Multi-Blade has been installed and tested on the CRISP reflectometer at the ISIS neutron and muon source in UK. The results on the detailed detector characterization are discussed in this manuscript.

The Multi-Blade Boron-10-based neutron detector performance using a focusing reflectometer

“…The shadowed wires have been removed, a region of lower intensity is normally observed because of the charge collection at the first wire of each cassette. The decrease in efficiency in this region is never worse than 50% and occurs in one wire, a detailed discussion can be found in [3]. A small intrinsic nonuniformity due to the modular design of the detector can be observed.…”

“…The ToF (T ) of each event is the time of arrival of a neutron to the specific wire (Y on the vertical axis). When (T ) has to be translated to neutron wavelength (λ), the physical depth (Z along the neutron incoming direction) of each wire must be taken into account [3].…”

“…The wavelength resolution is given by the pulse length of the source, because λ is encoded in the Time of Flight (ToF) [17] as described in section 2.2. The angular resolution (σ θ ) is determined by the detector spatial resolution (FWHM ∆Y ≈ 0.5 mm) and the sample-to-detector distance (L≈ 3.4 m), which gives σ θ ≈ 0.004 Note that these are not dead channels, it is instead the shadowing effect inherent to the detector geometry, a detailed description of which can be found in [3]. Physically the last firing wire of one cassette is adjacent to the first wire of the neighbour cassette.…”

“…The PHS recorded for neutron conversion in Boron has a characteristic shape defined by two peaks, which correspond to the energy released by the yields of the interaction, i.e. α or Li particles [3,48], background events, e.g. gamma-rays, result in a sharp peak at low energies.…”

“…A detailed characterization [2] of a Multi-Blade detector has been carried out at the Budapest Neutron Centre [35][36][37] in 2015. In 2017 a reflectometry demonstrator has been installed and tested at the neutron reflectometer CRISP [38] at the ISIS neutron and muon source in the UK [39][40][41] performing a full detector characterization along with specular and offspecular reflectivity measurements on several samples [3,4]. Moreover, background studies, in particular the response of this detector to fast neutrons [42] and gamma-rays [2], have been carried out at the Source Testing Facility (STF [43,44]) at the Lund University in Sweden.…”