Optimisation of the scintillation light collection and uniformity for the SoLid experiment

Abstract

A : This paper presents a comprehensive optimisation study to maximise the light collection efficiency of scintillating cube elements used in the SoLid detector. Very short baseline reactor experiments, like SoLid, look for active to sterile neutrino oscillation signatures in the anti-neutrino energy spectrum as a function of the distance to the core and energy. Performing a precise search requires high light yield of the scintillating elements and uniformity of the response in the detector volume. The SoLid experiment uses an innovative hybrid technology with two different scintillators: polyvinyltoluene scintillator cubes and 6 LiF:ZnS(Ag) screens. A precision test bench based on a 207 Bi calibration source has been developed to study improvements on the energy resolution and uniformity of the prompt scintillation signal of antineutrino interactions. A trigger system selecting the 1 MeV conversion electrons provides a Gaussian energy peak and allows for precise comparisons of the different detector configurations that were considered to improve the SoLid detector light collection. The light collection efficiency is influenced by the choice of wrapping material, the position of the 6 LiF:ZnS(Ag) screen, the type of fibre, the number of optical fibres and the type of mirror at the end of the fibre. This study shows that large gains in light collection efficiency are possible compared to the SoLid SM1 prototype. The light yield for the SoLid detector is expected to be at least 52±2 photo-avalanches per MeV per cube, with a relative non-uniformity of 6 %, demonstrating that the required energy resolution of at least 14 % at 1 MeV can be achieved.

eV-Scale Sterile Neutrinos

“…SoLid (86,117) is an experiment in preparation using 12800 cells made of cubes of polyvinyltoluene (PVT) of (5×5×5) cm 3 in dimension, partially coated with thin sheets of 6 LiF:ZnS(Ag) to capture and detect neutrons. The detector is installed at the surface level, about 6 m away from the 60 MW SCK·CEN BR2 research reactor in Belgium.…”

Development of a quality assurance process for the SoLid experiment

“…Each voxel comprises a PVT cube of 5×5×5 cm 3 in conjunction with two layers of ∼ 250 µm thick 6 LiF:ZnS(Ag), as illustrated in figure 1. This voxel configuration was defined after a dedicated study to improve the light collection of the planar sub-assemblies [22]. During construction of the voxel units, each PVT cube is cleaned, measured and weighted.…”

“…22 Na decays via β + (90.3%) and via electronic capture (9.64%) into 22 Ne as illustrated in figure 7. In almost all cases, 22 Na decays into the first excited state of 22 Ne, which in turn decays to its ground state via the emission of a 1.27 MeV gamma. Hence, in 90% of the 22 Na decays the emission of a positron in conjunction with a 1.27 MeV gamma occurs; however, the e + annihilates inside the source capsule, emitting two back-to-back 511 keV gammas.…”

“…In these runs the gain of each MPPC was measured, which increased linearly with the OV. The 22 Na source. In about 90% of cases it decays via β+ emission to the first excited state of 22 Ne, which in turn goes into its ground state through the emission of a 1.27 MeV gamma.…”

Short-baseline neutrino oscillations with 3 + 1 non-unitary mixing

“…The positive indication (32) in favor of the existence of new physics given by the combined analysis of the NEOS and DANSS data is under investigation in the ongoing STEREO [30], PROSPECT [31], SoLid [32], and Neutrino-4 [20] in the 3+1 non-unitary mixing (NUM) and 3+1 standard unitary mixing (STD) scenarios. (b) Exclusion curves of the CDHSW [37], CCFR [38], SciBooNE-MiniBooNE [39,40], and MINOS&MINOS+ in both the 3+1 non-unitary and standard unitary mixing scenarios and the total combined exclusion curve.…”