A novel segmented-scintillator antineutrino detector

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 6 LiF: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 6 LiF: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 1 on leave from CEADEN, Havana, Cuba 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.Keywords: antineutrino, sterile neutrino, 6 LiF:ZnSThe re-evaluation of reactorν e flux calculations that led to the so-called reactor anomaly [15,16,17] and the recent evidence for a deviation in theν e 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. New measurements at reactors, at closer distances than ever before, are needed to test possible explanations. The use of a highly segmented detector target to probe small

Prospects for improved understanding of isotopic reactor antineutrino fluxes

“…A number of HEU-based experiments have thus far not demonstrated the level of background rejection necessary to achieve the 1∶1 signal-to-background ratio (S:B) assumed in this study [46,55,57]. On the other hand, other short-baseline efforts have either already achieved a S:B ratio far surpassing 1∶1 at LEU reactors [56] or have presented prototype-and Monte Carlo-based evidence to support their achievement of a S:B of 1∶1 or higher at HEU reactors [35,37]. To examine the impact of the S:B on IBD yield precision, we adjust the assumed S:B of all short-baseline measurements in data sets 2-5, while continuing to neglect background contributions for the Daya Bay-like measurements of data sets 1-3.…”

“…A variety of new ton-scale compact reactor antineutrino experiments have either recently been deployed [55][56][57] or will be deployed in the near future [35][36][37] at short baselines from operating LEU [55,56] or HEU [35][36][37] reactors. These experiments' detectors incorporate a wide variety of detection technologies and background rejection techniques to detect an IBD signal despite sizable cosmogenic and ambient backgrounds in their near-surface, nearreactor environments.…”

“…We begin by considering a detector with 2 × 10 29 fiducial target protons and 44% IBD detection efficiency; these values roughly correspond to the size of the PROSPECT detector [35] and the IBD detection efficiency of the PROSPECT and Soliδ detectors [35,37]. We then consider deployment of this detector at an HEU and LEU reactor site.…”

“…In the coming years, a new generation of short-baseline experiments based at highly enriched uranium reactors will obtain new data sets to directly probe sterile neutrino oscillations and measureν e production by 235 U [35][36][37]. A number of recent analyses have attempted to exploit differences in reactor fuel content between data sets; by comparing measurements of differing mixtures of Puν e fluxes at low-enriched (LEU) reactors or these to measurements of pure 235 U-produced fluxes at highly enriched (HEU) reactors, these analyses have probedν e production rates by individual fission isotopes.…”

The SoLid short baseline neutrino detector

“…At this temperature, we expect to reduce dark-count rate by a factor of 10, decreasing the sustainable lower limit in term of number of peak over threshold. With this trigger system, operated in a cooled environement, SoLid neutron reconstruction efficiency goal is 70 %, corresponding to our 30 % IBD efficiency target [5]. All the last improvement discussed here are designed for this purpose [4].…”