Abstract
The next generation of very-short-baseline reactor experiments will require compact detectors operating at surface level and close to a nuclear reactor. This paper presents a new detector concept based on a composite solid scintillator technology. The detector target uses cubes of polyvinyltoluene interleaved with 6LiF:ZnS(Ag) phosphor screens to detect the products of the inverse beta decay reaction. A multi-tonne detector system built from these individual cells can provide precise localisation of scintillation signals, making efficient use of the detector volume. Monte Carlo simulations indicate that a neutron capture efficiency of over 70 % is achievable with a sufficient number of 6LiF:ZnS(Ag) screens per cube and that an appropriate segmentation enables a measurement of the positron energy which is not limited by γ-ray leakage. First measurements of a single cell indicate that a very good neutron-gamma discrimination and high neutron detection efficiency can be obtained with adequate triggering techniques. The light yield from positron signals has been measured, showing that an energy resolution of 14%/√E(MeV) is achievable with high uniformity. A preliminary neutrino signal analysis has been developed, using selection criteria for pulse shape, energy, time structure and energy spatial distribution and showing that an antineutrino efficiency of 40% can be achieved. It also shows that the fine segmentation of the detector can be used to significantly decrease both correlated and accidental backgrounds.
Highlights
Short-distance νe detectionThe re-evaluation of reactor νe flux calculations that led to the so-called reactor anomaly [15,16,17] and the recent evidence for a deviation in the νe energy spectrum shape, observed by three short baseline experiments (∼ 1-2 km) [18,19,20], has put our understanding of the reactor flux model into question
: The generation of very-short-baseline reactor experiments will require compact detectors operating at surface level and close to a nuclear reactor
Monte Carlo simulations indicate that a neutron capture efficiency of over 70 % is achievable with a sufficient number of 6LiF:ZnS(Ag) screens per cube and that an appropriate segmentation enables a measurement of the positron energy which is not limited by γ-ray leakage
Summary
The re-evaluation of reactor νe flux calculations that led to the so-called reactor anomaly [15,16,17] and the recent evidence for a deviation in the νe energy spectrum shape, observed by three short baseline experiments (∼ 1-2 km) [18,19,20], has put our understanding of the reactor flux model into question. The detector technology is based on a combination of plastic and inorganic scintillators with a segmentation and geometry that provides a high neutron detection efficiency, an accurate energy measurement and maximises the signal-to-noise ratio for IBD events This detector technology will be used in a generation very short baseline experiment called SoLid (Search for Oscillations with a 6Li detector). The components described above allow for a relatively inexpensive and modular tonne-scale detector system that provides adequate containment of the neutron capture scintillation signal — around a hundred times better than a LS + Gd detector, in terms of the volume needed to contain the scintillation signal — and a robust and precise three-dimensional positioning of both positrons and neutrons To illustrate these capabilities a large sample of IBD interactions was simulated in a 1 m3 SoLid detector, comprising 20 detection planes with a surface of 1 m2 each. Simulation results show that the addition of a 5 cm polyethylene neutron reflector, surrounding the whole detector volume, improves the overall neutron capture efficiency by 7% and by 30% in the layers closest to the edge of the detector
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