by Dr Daniel Saunders
(Imperial College London)

The disappearance of reactor antineutrinos into a new neutral state (called the sterile neutrino) has been proposed as a possible explanation for the recent reactor and Gallium anomalies arising from the re-analysis of reactor flux and calibration data of previous neutrino experiments. One way to test this hypothesis is to look for distortions of the anti-neutrino energy caused by oscillation from active to sterile neutrino at close stand-off (~ 6-8m) of a compact reactor core. Due to the small anti-neutrino cross-section, the main challenge in achieving a precise measurement is to control the high level of gamma rays and neutron background that are present at close stand off and to the surface.

The SoLid experiment is searching for active-to-sterile anti-neutrino oscillations at a very short baseline of the SCK CEN BR2 research reactor. A novel approach to measuring reactor anti-neutrinos has been developed based on an innovative sandwich of composite Polyvynil-Toluene and 6LiF:ZnS scintillators. The system is highly segmented and read out by a two-dimensional network of wavelength shifting fibers and MPPCs. High experimental sensitivity can be achieved with the combination of high granularity, high neutron-gamma discrimination using 6LiF:ZnS(Ag) scintillator and precise localisation of the inverse beta decay products. We will describe the principle of detection, the research and development to arrive at the final detector design, and focus on the recent deployment of the detector at the BR2 reactor.