The neutrino is one of the elementary particles. In the field of particle physics, the question of whether neutrinos have mass has existed for many years. In 1998, the Super-Kamiokande experiment ...made the first discovery of the neutrino oscillation using the atmospheric neutrino anomaly. It was direct evidence of neutrino mass. Recently, more precise measurements of neutrino oscillation parameters have been performed using not only atmospheric neutrinos but also neutrinos from the Sun, accelerators and reactors. The detection of the next supernova neutrino is awaited and is expected to improve our understanding of the death of the massive stars. The history and the current status of neutrino physics, especially with respect to the Super-Kamiokande experiment and the potential of the Hyper-Kamiokande experiment were presented in the lecture.
Abstract
This paper reports the development and detailed properties of about 13 metric tons of gadolinium sulfate octahydrate, $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, which has been dissolved into ...Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ on diffuse supernova neutrino background searches and solar neutrino observation and confirm the need to reduce radioactive and fluorescent impurities by about three orders of magnitude from commercially available high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$. In order to produce ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$, we have developed a method to remove impurities from gadolinium oxide, Gd2O3, consisting of acid dissolution, solvent extraction, and pH control processes, followed by a high-purity sulfation process. All of the produced ultra-high-purity $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ is assayed by inductively coupled plasma mass spectrometry and high-purity germanium detectors to evaluate its quality. Because of the long measurement time of high-purity germanium detectors, we have employed several underground laboratories for making parallel measurements including the Laboratorio Subterráneo de Canfranc in Spain, Boulby in the UK, and Kamioka in Japan. In the first half of production, the measured batch purities were found to be consistent with the specifications. However, in the latter half, the $\rm Gd_2(\rm SO_4)_3\cdot \rm 8H_2O$ contained one order of magnitude more 228Ra than the budgeted mean contamination. This was correlated with the corresponding characteristics of the raw material Gd2O3, in which an intrinsically large contamination was present. Based on their modest impact on SK physics, they were nevertheless introduced into the detector. To reduce 228Ra for the next stage of gadolinium loading to SK, a new process has been successfully established.
A Beam Induced Fluorescence (BIF) monitor is being developed as an essential part of the monitor update toward MW beam power operation at the J-PARC neutrino beam line, where a 30 GeV proton beam is ...extracted, bent and struck onto a 90-cm-long graphite target to produce an intense and nearly pure muon (anti-)neutrino beam for the Tokai-to-Kamioka(T2K) experiment. A BIF monitor can measure the proton beam profile non-destructively and continuously spill-by-spill with fluorescence light produced by proton-N2 interactions. In order to generate enough light to measure the profile precisely, it is necessary to temporarily increase the vacuum pressure near the BIF interaction point up to ~ 10−2 Pa during each beam spill while keeping the average pressure low (10−4 to 10−6 Pa) at other locations to protect vacuum equipment. Therefore, R&D of a pulsed gas injection system satisfying these requirements is in progress. We will report the recent R&D status of the gas injection system and prospects toward operation of a prototype monitor which we plan to install this fall 2019.
A high performance distillation system to remove krypton from xenon was constructed, and a purity level of Kr/Xe
=
∼3
×
10
−12 was achieved. This development is crucial in facilitating ...high-sensitivity low-background experiments such as the search for dark matter in the universe.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches in the absence of an externally applied electric field. ...PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background by a factor of 7.7±1.1(stat)±0.61.2(sys)×10−2 at energies between 4.8 and 7.2keVee and 7.7±2.8(stat)±2.82.5(sys)×10−3 at energies between 9.6 and 12keVee for a scintillation light yield of 20.9photoelectrons/keVee. Further study was done by masking some of that light to reduce this yield to 4.6photoelectrons/keVee. Under these conditions the same method results in an electron event reduction by a factor of 2.4±0.2(stat)±0.20.3(sys)×10−1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Fast neutrons are a large background to measurements of gamma-rays emitted from excited nuclei, such that detectors that can efficiently distinguish between the two are essential. In this ...paper we describe the separation of gamma-rays from neutrons with the pulse shape information of the CsI(Tl) scintillator, using a fast neutron beam and several gamma-ray sources. We find that a figure of merit optimized for this separation takes on large and stable values (nearly 4) between 5 and 10 MeV of electron equivalent deposited energy, the region of most interest to the study of nuclear de-excitation gamma-rays. Accordingly, this work demonstrates the ability of CsI(Tl) scintillators to reject neutron backgrounds to gamma-ray measurements at these energies.
Radon removal from gaseous xenon with activated charcoal Abe, K.; Hieda, K.; Hiraide, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
2012, 2012-01-00, 20120101, Volume:
661, Issue:
1
Journal Article
Peer reviewed
Many low background experiments using xenon need to remove radioactive radon to improve their sensitivities. However, no method of continually removing radon from xenon has been described in the ...literature. We studied a method to remove radon from xenon gas through an activated charcoal trap. From our measurements we infer a linear relationship between the mean propagation velocity
v
Rn
of radon and
v
Xe
of xenon in the trap with
v
Rn
/
v
Xe
=
(
0.96
±
0.10
)
×
10
−
3
at −85
°C. As the mechanism for radon removal in this charcoal trap is its decay, knowledge of this parameter allows us to design an efficient radon removal system for the XMASS experiment. The verification of this system found that it reduces radon by a factor of 0.07, which is in line with its expected average retention time of 14.8 days for radon.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
Demand to use gadolinium (Gd) in detectors is increasing in the field of elementary particle physics, especially in neutrino measurements and dark matter searches. Large amounts of Gd are ...used in these experiments. To assess the impact of Gd on the environment it is becoming important to measure the baseline concentrations of Gd. Such measurement, however, is not easy due to interference by other elements. In this paper a method for measuring the concentrations of rare earth elements, including Gd, is proposed. In the method, inductively coupled plasma-mass spectrometry is utilized after collecting the dissolved elements in chelating resin. Results of the ability to detect anomalous concentrations of rare earth elements in river water samples in the Kamioka and Toyama areas are also reported.
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