Development of a quality assurance process for the SoLid experiment

The SoLid experiment has been designed to search for an oscillation pattern induced bya light sterile neutrino state, utilising the BR2 reactor of SCK•CEN, in Belgium.The detector leverages a new hybrid technology, utilising two distinct scintillators in a cubicarray, creating a highly segmented detector volume. A combination of 5 cm cubic polyvinyltoluenecells, with6LiF:ZnS(Ag) sheets on two faces of each cube, facilitate reconstruction of the neutrinosignals. Whilst the high granularity provides a powerful toolset to discriminate backgrounds; byitself the segmentation also represents a challenge in terms of homogeneity and calibration, fora consistent detector response. The search for this light sterile neutrino implies a sensitivity todistortions of aroundO(10)% in the energy spectrum of reactorνe. Hence, a very good neutrondetection efficiency, light yield and homogeneous detector response are critical for data validation.The minimal requirements for the SoLid physics program are a light yield and a neutron detectionefficiency larger than 40 PA/MeV/cube and 50% respectively. In order to guarantee these minimalrequirements, the collaboration developed a rigorous quality assurance process for all 12800 cubiccells of the detector. To carry out the quality assurance process, an automated calibration systemcalled CALIPSO was designed and constructed. CALIPSO provides precise, automatic placementof radioactive sources in front of each cube of a given detector plane (16×16 cubes). A combinationof22Na,252Cf and AmBe gamma and neutron sources were used by CALIPSO during the qualityassurance process. Initially, the scanning identified defective components allowing for repair duringinitial construction of the SoLid detector. Secondly, a full analysis of the calibration data revealedinitial estimations for the light yield of over 60 PA/MeV and neutron reconstruction efficiency of68%, validating the SoLid physics requirements.