Boron-loaded Liquid Scintillator Research Articles

The DarkSide-50 outer detectors

DarkSide-50 is a dark matter detection experiment searching for Weakly Interacting Massive Particles (WIMPs), in Gran Sasso National Laboratory. For experiments like DarkSide-50, neutrons are one of the primary backgrounds that can mimic WIMP signals.The experiment consists of three nested detectors: a liquid argon time projection chamber surrounded by two outer detectors. The outermost detector is a 10 m by 11 m cylindrical water Cherenkov detector with 80 PMTs, designed to provide shielding and muon vetoing.Inside the water Cherenkov detector is the 4 m diameter spherical boron-loaded liquid scintillator veto, with a cocktail of pseudocumene, trimethyl borate, and PPO wavelength shifter, designed to provide shielding, neutron vetoing, and in situ measurements of the TPC backgrounds. We present design and performance details of the DarkSide-50 outer detectors.

The veto system of the DarkSide-50 experiment

Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like WIMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

Detecting fast and thermal neutrons with a boron loaded liquid scintillator, EJ-339A

A commercial boron-loaded liquid scintillator EJ-339 A was studied, using a 252Cf source with/without polyethylene moderator, to examine the possibility of discriminating slow-neutron induced events in 10B from fast-neutron events, resulting from proton recoils, and gamma-ray events. Despite the strong light quenching associated with neutron induced events in 10B, correct classification of these events is shown to be possible with the aid of digital signal processing.

A Novel Boron-Loaded Liquid Scintillator for Neutron Detection

A boron-loaded liquid scintillator (LS) has been optimized for neutron detection application in a high gamma field environment. It is composed of the solvent linear alkylbenzene (LAB), a boroncontaining material, o-carborane (C2B10H12); a fluor, 2,5-diphenyloxazole (PPO); and a wavelength shifter, 1,4-bis[2-methylstyryl] benzene (bis-MSB). Preparation of the liquid scintillator and optimization of its chemical composition are described. The boronloaded LS has been tested with a neutron beam at the National Research Universal (NRU) reactor. A peak at an equivalent energy of 60 keV is observed in the energy spectrum and is attributed to neutrons. The results confirm the possibility of using B-10 loaded scintillator as a sensitive medium for neutron detection in a relatively large background of gamma rays.

A highly efficient neutron veto for dark matter experiments

We present a conceptual design for an active neutron veto, based on boron-loaded liquid scintillator, for use in direct-detection dark matter experiments. The simulated efficiency of a 1m thick veto is greater than 99.5% for background events produced by radiogenic neutrons, while the background due to externally produced cosmogenic neutrons is reduced by more than 95%. The ability of the veto to both significantly suppress, and provide in situ measurements of, these two dominant sources of background would make the next generation of dark matter experiments much more robust, and dramatically improve the credibility of a dark matter detection claim based on the observation of a few recoil events. The veto would also allow direct extrapolation between the background-free operation of a small detector and the physics reach of a larger detector of similar construction.

A feasibility study of boron-loaded liquid scintillator for the detection of electron anti-neutrinos

Boron-loaded liquid scintillator offers some potential advantages as a detector for electron anti-neutrinos. A research program was carried out with the objective of developing such scintillators. The crucial feature is the pulse shape discrimination properties following the neutron capture by 10B. Results of the R&D efforts are presented. The feasibility and the technical difficulties of carrying out a full-scale neutrino experiment based on this approach are discussed.

Energy response of a full-energy-absorption neutron spectrometer using boron-loaded liquid scintillator BC-523

The energy response of a full-energy-absorption neutron spectrometer using boron-loaded liquid scintillator BC-523 was examined for the neutron energy range between 1.2 and 14 MeV. Pulse height spectra measured with monoenergetic neutrons evidenced that they were characterized by either a single peak with a shoulder or by double peaks. A Monte Carlo simulation of the neutron behavior in the detector reproduced the spectra by considering the nonlinear light yield against recoil proton energy. Detection efficiencies ranging from 10% for 1.2 MeV to 0.6% for 14 MeV neutrons were obtained with a 12.7 cm diameter × 7.6 cm long scintillator. A high background rejection with a ratio of 2200 to 1 obtained without using any γ-shielding makes the present neutron spectrometer attractive for the application to low-level environmental neutron measurements.

Effects of elastic scattering on the low energy neutron detection efficiency of a lithium glass and boron-loaded liquid scintillator

The neutron detection efficiencies of a lithium glass and a boron-loaded liquid scintillation detector were calibrated over the energy range from thermal to 8 keV. The calibrations were based on the measurement of a known spectrum from the low power experimental reactor facility MOATA and detailed three-dimensional Monte Carlo calculations. For both detectors good agreement was obtained between their measured and calculated efficiencies. Elastic scattering within the lithium glass produced an enhancement of the detection efficiency in the epithermal region and this enhancement increased with energy. A significant distortion of the measured spectrum arose from the scattering of neutrons into the detectors by the surrounding shielding materials.

Boron-Loaded Neutron Detector with Very Low γ-Ray Sensitivity

A boron-loaded liquid scintillator is described which gives a much greater difference in the pulse shapes for γ rays and for slow neutrons than any of the liquids currently used. A detailed study of the pulse shapes indicates that the γ-ray sensitivity of a neutron detector filled with this liquid can be reduced by a factor of 500 with only a 5% decrease in the neutron sensitivity by application of pulse-shape discrimination. A survey of the pulse-shape characteristics of a number of scintillators currently used, together with the results for the new liquid, is presented, and the performance of the new detector with a simple system of pulse-shape discrimination is described.

Boron-Loaded Liquid Scintillation Neutron Detectors

The general problems involved in constructing boron-loaded liquid scintillation neutron detectors are considered. The characteristics of particular counters which have been successfully used in neutron transmission measurements by the time-of-flight method are then described. The design of these counters was guided by the results of a Monte Carlo study of neutron capture in a boron-poisoned medium. This calculation gives the probability of neutron capture as a function of neutron energy, counter thickness, and time. The calculated results are compared with experimentally determined efficiencies. The advantages and problems encountered in using the boron-loaded liquid scintillator with the Argonne fast neutron chopper are discussed.