Gamma- and Fast Neutron- Sensitivity of 10B-based Neutron Detectors at ESS

  • Francesco Messi (Speaker)

Activity: Talk or presentationPresentation

Description

The European Spallation Source (ESS), presently under construction in Lund, Sweden, is designed to be the world’s brightest neutron source. When it will be in operation, ESS will deliver an instantaneous neutron flux on detectors that will be without precedent. A down side of the high brightness will be the increase of background, especially from gamma-rays and fast-neutrons.
Considering that scattering cross-sections of many samples tend to be relatively low and that the gamma- and fast- neutron- backgrounds tend to be considerable high at spallation facilities [Che+14], the signal-to-noise ratio of a measurement needs to be maximised. The sensitivity of a thermal-neutron detector to gamma-rays and to fast- neutrons is a very important characteristic, as it defines the best achievable signal-to-noise ratio for the measurement. It is therefore crucial to measure the gamma- and fast-neutron- sensitivities of all detectors that will be installed on the instruments at ESS.
New detector technologies have been implemented to face the challenges arising with the new frontiers of ESS; in particular, gas detectors with solid thin-film neutron converters readout by a gas proportional counter method have been proposed as an appropriate choice for many of the ESS instruments. The gamma-sensitivity of the MultiGrid [Kha+12] detector has been measured in 2013 and shows that an equal gamma-ray rejection to that of 3He tubes is achieved with the new technology [Kha+13].
An extension of these measurements has been performed on the MultiBlade [Pis+14] detector beginning of this year [Pis+17]. The MultiBlade is a 10B-based detector developed for Reflectometry applications. It consists of a stack of Multi Wire Proportional Chambers (MWPC) operated at atmospheric pressure with continuous gas flow (Ar/CO2, 80/20 mixture). The expected instantaneous local flux at the detector is between 105 and 5 × 105/s/mm2.
With the results from the test performed at the Source Testing Facility (SRF) of Lund University, Sweden, at the end of last year, we have shown that the gamma-sensitivity for this kind of detector is below 10−7 (for 100 keV threshold). The methodology of the tests together with a discussion on the results will be presented in this talk.
At present we are measuring the fast-neutron-sensitivity of the MultiBlade detector. We are using the neutron sources available at the STF and we are applying different techniques, including tagged and non tagged fast neutron. [Sch+16b; Sch+15; Sch+16a; Sch+16c]
All these tests will be presented in the talk and the results discussed in details.
These measurements are crucial to validate the detector technology to be installed at ESS as well as at any other instruments at Neutron Scattering Science Facilities and are of general interest for all kinds of 10B-based neutron detectors.
Period2017 Oct 212017 Oct 28
Event title2017 IEEE Nuclear Science Symposium & Medical Imaging Conference
Event typeConference
LocationAtlanta, GeorgiaShow on map
Degree of RecognitionInternational