Loaded Liquid Scintillator Research Articles

Development of a new tellurium loaded liquid scintillator based on linear alkylbenzene

The R&D results of new tellurium loaded liquid scintillators based on linear alkylbenzene are presented in this work. For the first time, diphenyltellurium dicarboxylates (dipivalate, diisovalerate, di-2-ethylhexanoate) are used as tellurium-containing additives. The optical properties (transparency, light yield) of the scintillator have been studied depending on the tellurium concentration, comprehensive studies have been carried out to optimize the composition of the scintillator, the effect of the secondary scintillation solvent on the light yield has been studied, and the long-term stability of Te-LS has been finally established.

The JSNS[formula omitted] detector

The JSNS2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for oscillations involving a sterile neutrino in the eV2 mass-splitting range. The experiment will search for the appearance of electron antineutrinos oscillated from muon antineutrinos. The electron antineutrinos are detected via the inverse beta decay process using a liquid scintillator detector. A 1MW beam of 3GeV protons incident on a spallation neutron target produces an intense and pulsed neutrino source from pion, muon, and kaon decay at rest. The JSNS2 detector is located 24m away from the neutrino source and began operation from June 2020. The detector contains 17 tonnes of gadolinium (Gd) loaded liquid scintillator (LS) in an acrylic vessel, as a neutrino target. It is surrounded by 31 tonnes of unloaded LS in a stainless steel tank. Optical photons produced in LS are viewed by 120 R7081 Hamamatsu 10-inch Photomultiplier Tubes (PMTs). In this paper, we describe the JSNS2 detector design, construction, and operation.

Slow control and monitoring system at the JSNS2

Abstract The Sterile Neutrino Search at the J-PARC Spallation Neutron Source (JSNS$^2$) experiment aims to search for sterile neutrino oscillations using a neutrino beam from muon decays at rest. The JSNS$^2$ detector contains 17 tons of 0.1$\%$ gadolinium (Gd) loaded liquid scintillator (LS) as a neutrino target. Detector construction was completed in the spring of 2020. A slow control and monitoring system (SCMS) was implemented for reliable control and quick monitoring of the detector operational status and environmental conditions. It issues an alarm if any of the monitored parameters exceed a preset acceptable range. The SCMS monitors the high voltage of the photomultiplier tubes, the LS level in the detector, possible LS overflow and leakage, the temperature and air pressure in the detector, the humidity of the experimental hall, and the LS flow rate during filling and extraction. An initial 10 days of data-taking with a neutrino beam was done following a successful commissioning of the detector and SCMS in 2020 June. In this paper, we present a description of the assembly and installation of the SCMS and its performance.

The JSNS2 data acquisition system

The JSNS2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24 m short baseline at J-PARC. The JSNS2 inner detector is filled with 17 tons of gadolinium(Gd)-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate γ-catcher and an optically separated outer veto volumes. A total of 120 10-inch photomultiplier tubes observe the scintillating optical photons and each analog waveform is stored with flash analog-to-digital converters. We present details of the data acquisition, processing, and data quality monitoring system. We also present two different trigger logics which are developed for the beam and self-trigger.

Inner balloon production for KamLAND-Zen 800

KamLAND-Zen searches for neutrinoless double-beta decay with 136Xe loaded liquid scintillator (LS). The LS container, a 25-μm-thick clean nylon inner balloon is a key of the experiment since one of the main backgrounds in the ROI is 214Bi from the inner balloon. In KamLAND-Zen 400 (operated from 2011 to 2015), dust contamination of the inner balloon from the environment limited the sensitivity, although the inner balloon was fabricated at a class-1 super clean room. We improved the production method of the inner balloon for KamLAND-Zen 800 (started DAQ in January, 2019) and successfully reduced the 214Bi background level to one fifteenth as compared to the 2nd phase of KamLAND-Zen 400. The inner balloon film material and requirements, improved fabrication scheme, including establishment of clean environment and dust control, will be described.

Scintillation balloon for liquid scintillator base Neutrinoless double beta decay search experiments

A liquid scintillator base experiment KamLAND-Zen has set a lower limit on neutrinoless double beta decay half-life, and upgrade project KamLAND-Zen 800 has started in 2019. Unfortunately this project expects some backgrounds, and one of the main backgrounds is β/γ-ray from 214Bi in container of xenon loaded liquid scintillator (mini-balloon). In order to reject the background, we suggest using scintillation film for the future mini-balloon. If we can tag α-ray from 214Po by scintillation detection, we can eliminate 214Bi events by delayed coincidence analysis.Recently, it was reported that polyethylene naphthalate (PEN) can be used as a scintillator with blue photon emission. PEN has chemical compatibility for strong solvent, thus it has a possibility to use in liquid scintillator. In this presentation, we will mention the results for feasibility studies about transparency and emission spectra, light yield, radioactivity, strength of film etc.. We also show the test-sized scintillation balloon with an 800-mm diameter and discussions about how to use the scintillation balloon in KamLAND.

First results of KamLAND-Zen 800

KamLAND-Zen is a neutrinoless double beta decay (0vββ) search experiment using xenon 136 and ultra-low background environment of KamLAND (Kamioka Liquid scintillator Anti-Neutrino Detector). KamLAND-Zen collaboration has prepared the KamLAND-Zen 800 project with almost 750 kg of xenon and cleaner container for xenon loaded liquid scintillator. The container production was started in May 2017 and KamLAND-Zen 800 data acquisition was started in January 2019. In this paper, we will describe the KamLAND-Zen 800 project and report on the detector condition, data quality, the first analysis results, and the prospects.

Liquid scintillator for search of double beta decay with Tin

Sn-124 is one of the double beta decay isotopes where no measurement of the 2νββ decay rate has been performed. The abundance of the isotope is 5.79%, fairly low, however it can be compensated for by the high loading potential of the natural isotope up to 10% into liquid scintillator without significant light quenching. This work presents results of the LAB based tin loaded liquid scintillator: stability, light yield and possible purification techniques.

Improved STEREO simulation with a new gamma ray spectrum of excited gadolinium isotopes using FIFRELIN

.The STEREO experiment measures the electron antineutrino spectrum emitted in a research reactor using the inverse beta decay reaction on H nuclei in a gadolinium loaded liquid scintillator. The detection is based on a signal coincidence of a prompt positron and a delayed neutron capture event. The simulated response of the neutron capture on gadolinium is crucial for the comparison with data, in particular in the case of the detection efficiency. Among all stable isotopes, 155Gd and 157Gd have the highest cross sections for thermal neutron capture. The excited nuclei after the neutron capture emit gamma rays with a total energy of about 8MeV. The complex level schemes of 156Gd and 158Gd are a challenge for the modeling and prediction of the deexcitation spectrum, especially for compact detectors where gamma rays can escape the active volume. With a new description of the Gd (n, gamma) cascades obtained using the FIFRELIN code, the agreement between simulation and measurements with a neutron calibration source was significantly improved in the STEREO experiment. A database of ten millions of deexcitation cascades for each isotope has been generated and is now available for the user.

Aging study of Gd concentration in LAB-based Gd loaded liquid scintillator exposed to passivated stainless steel

Stainless steel is a candidate of the inner surface of the storage container for LAB-based Gadolinium loaded liquid scintillator (Gd-LS) to be used in the JSNS2 neutrino detector. Aging effect on Gd concentration of Gd-LS was investigated with the Gd-LS sample stored in the passivated stainless steel bottle by two independent methods. The direct comparison of the neutron capture time measurement showed that there is no significant degradation of the capture time after 617 days aging. Titration was performed to measure Gd concentration, and the result after 466 days aging is consistent with the result before aging within the uncertainty of the measurement. Both results lead to a conclusion that stainless steel is usable for Gd-LS storage for JSNS2 experiment.

Double Beta Decay Experiments With Loaded Liquid Scintillator

Liquid scintillator detectors have many properties which are highly advantageous for neutrino research at the MeV energy scale. There are various choices of additives to an organic liquid scintillator which typically function as the nuclear targets in a neutrino interaction. More recently, new techniques for loading a large amount of nuclei into liquid scintillator enable sensitive searches for double beta decay with various nuclei. KamLAND was an existing detector constructed for neutrino physics at the MeV scale, later upgraded to a sensitive detector for double beta decay (KamLAND-Zen). In this experiment, isotopically enriched xenon gas was loaded into the highly radiopure liquid scintillator. As xenon is a stable noble gas, the scintillation performance changes little, and it is safe for long-term use. To mitigate backgrounds, xenon was loaded only into the liquid scintillator in the central part of the detector, contained in a small nylon balloon. Owing to the large amount of xenon and low background level, the KamLAND-Zen experiment achieved the most sensitive search to date for neutrinoless double beta decay. The next phase of the experiment plans to increase the amount of xenon by almost double. In the future, sensitivity can be further enhanced by detector upgrades. SNO+ (successor to the Sudbury Neutrino Observatory) is a liquid scintillator detector that is currently being commissioned and will soon be taking data. Originally, SNO+ developed a technique to load neodymium into the liquid scintillator in order to conduct a double beta decay search with the isotope $^{150}$Nd. Later, SNO+ developed two new techniques that enable loading tellurium into liquid scintillator. The large natural abundance of $^{130}$Te and the ability to load tellurium at a significant concentration in the SNO+ liquid scintillator, while maintaining excellent scintillation optical properties, offer the prospect of a very sensitive search for neutrinoless double beta decay. This article will discuss both experiments, KamLAND-Zen and SNO+, highlighting the results achieved, the techniques involved in loading the liquid scintillator, and describing the purification of components of the loaded liquid scintillator to very low background levels.

Status of balloon production for KamLAND-Zen 800 kg phase

KamLAND-Zen is an experiment for neutrinoless double beta decay (0ν2β) search with 136Xe, based on the large liquid scintillator detector KamLAND. KamLAND-Zen includes 16.5m3 xenon loaded liquid scintillator in a 3.16m diameter nylon balloon (inner-balloon) with 25μm wall thickness.KamLAND-Zen 400 (383kg 136Xe used) released a lower limit on the 0ν2β half-life of 136Xe. However, the sensitivity is limited by the contamination of radioactive backgrounds from the inner-balloon. Then, we planned KamLAND-Zen 800, upgrading the detector with a new inner-balloon of 3.84m diameter with 800kg 136Xe and 31.4m3 liquid scintillator.We present the current status of KamLAND-Zen, the new mini-balloon construction and methods to avoid background contaminations. In addition, the development of a scintillating balloon for future upgrades in order to remove the radioactive decay chain daughter nuclei bismuth is also introduced.

Relative light yield of liquid scintillator and gadolinium-loaded liquid scintillator

Relative light yield of linear alkyl benzene (LAB)-based gadolinium-loaded liquid scintillator (GdLS) and LAB-based non-gadolinium loaded liquid scintillator (LS) is an important parameter of the GdLS antineutrino detector, which was developed and applied to precisely measure the neutrino oscillation parameter in the current reactor neutrino experiments. We introduce a method which can precisely measure the relative light yield of liquid scintillators. By comparing the peak value of the energy spectrum of recoiled electrons, the light yield of the LS is measured to be 3.6 ± 2.0 %higher than the 0.1 %-by-weight GdLS.

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.

Development of a gadolinium-loaded liquid scintillator for the Hanaro short baseline prototype detector

We propose a new experiment on the site of the Korea Atomic Energy Research Institute (KAERI) located at Daejeon, Korea. The Hanaro short baseline (SBL) nuclear reactor with a thermal power output 30 MW is used to investigate a reactor neutrino anomaly. A Hanaro SBL prototype detector having a 60-l volume has been constructed ∼6 m away from the reactor core. A gadolinium (Gd)-loaded liquid scintillator (LS) is used as an active material to trigger events. The selection of the LS is guided by physical and technical requirements, as well as safety considerations. A linear alkyl benzene (LAB) is used as a base solvent of the Hanaro SBL prototype detector. Three g/l of PPO and 30 mg/l of bis-MSB are dissolved to formulate the LAB-based LS. Then, a 0.5% gadolinium (Gd) complex with carboxylic acid is loaded into the LAB-based LS by using the liquidliquid extraction method. In this paper, we will summarize all the characteristics of the Gd-loaded LAB-based LS for the Hanaro prototype detector.

Production and optical properties of Gd-loaded liquid scintillator for the RENO neutrino detector

Reactor experiment for neutrino oscillation (RENO) began data-taking from August 2011. It successfully observed reactor antineutrino disappearance in April 2012 to measure the smallest mixing angle of θ13. Two identical detectors, one at near location and the other at far location, are constructed at the Yonggwang nuclear power plant in South Korea, to compare the observed reactor neutrino fluxes. Each RENO detector is filled with 16 mass tons of Gadolinium loaded liquid scintillator (GdLS) in the neutrino target region, and with 28 mass tons of unloaded liquid scintillator (LS) in the γ-catcher region surrounding the target. LS was developed to satisfy chemical, physical, optical properties, and safety requirements. Linear alkyl benzene (LAB) was chosen as a solvent because of its high flash-point, sufficient light yield, and being environmentally friendly. GdLS is carefully developed to keep a long attenuation length and high light yield for a long time period. In this paper, we report the characteristics and mass production of the RENO LS and GdLS.

Liquid Scintillator based experiments in Neutrinoless Double Beta Decay

Recent experiments have confirmed neutrino oscillations. The mass structure of neutrinos is one of the next interesting subjects in neutrino physics. Neutrinoless double beta decay has the potential to investigate the mass structure of neutrinos. Many neutrinoless double beta decay experiments are being proposed and some were introduced at this conference. Here we present neutrinoless double beta decay experiments based on liquid scintillator techniques. SNO+ plans to use 150Nd as the neutrinoless double beta decay isotope dissolved in liquid scintillator, similarly KamLAND-Zen will use 136Xe loaded liquid scintillator. The physics goals, schedule and current status of both experiments were discussed.

A study of reactor neutrino monitoring at the experimental fast reactor JOYO

We carried out a study of neutrino detection at the experimental fast reactor JOYO using a 0.76 tons gadolinium loaded liquid scintillator detector. The detector was set up on the ground level at 24.3 m from the JOYO reactor core of 140 MW thermal power. The measured neutrino event rate from reactor on–off comparison was 1.11±1.24(stat.)±0.46(syst.) events/day. Although the statistical significance of the measurement was not enough, backgrounds in such a compact detector at the ground level were studied in detail and MC simulations were found to describe the data well. A study for improvement of the detector for future such experiments is also shown.

Status of RENO Experiment

An experiment, RENO (Reactor Experiment for Neutrino Oscillation), is under construction to measure the smallest and unknown neutrino mixing angle ( θ 13 ) using anti-neutrinos emitted from the Yonggwang nuclear power plant in Korea. The experimental setup consists of two identical 16-ton Gadolinium loaded liquid scintillator detectors located near and far from the reactor array to measure the deviations from the inverse square distance law. The experiment is planned to start data-taking in early 2011. An estimated systematic uncertainty associated with the measurement is less than 0.6%. Based on three years of data, it would be sensitive to measure the neutrino mixing angle in the range of s i n 2 ( 2 θ 13 ) > 0.02 . In this talk, the status of RENO experiment is described.

Comparison of Neutron Detection Efficiency of a He-3 Counter and a Boron-10 Loaded Liquid Scintillator

Performance of a He-3 counter and a B-10 loaded liquid scintillator EJ309B5 has been studied in terms of neutron detection efficiency. The measurements were carried out in a mixed field of neutron and gamma radiation from an intense ( ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> neutrons/s/4π) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">252</sup> Cf source. The response of both detectors to background and high intensity gamma radiation ( ~ 100 μSv/h at a detector) from a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sup> Co source has been measured to establish background count rate and gamma rays cut-off point, respectively. The analysis showed that the properties of a He-3 counter are significantly better than that of EJ309B5. However, it has been pointed out how to improve the performance of a liquid scintillator in order to reduce gamma radiation sensitivity.