XMASS-I is a single-phase liquid xenon detector whose purpose is direct detection of dark matter. To achieve the low background requirements necessary in the detector, a new model of photomultiplier ...tubes (PMTs), R10789, with a hexagonal window was developed based on the R8778 PMT used in the XMASS prototype detector. We screened the numerous component materials for their radioactivity. During development, the largest contributions to the reduction of radioactivity came from the stem and the dynode support. The glass stem was exchanged to the Kovar alloy one and the ceramic support were changed to the quartz one. R10789 is the first model of Hamamatsu Photonics K. K. that adopted these materials for low background purposes and provided a groundbreaking step for further reductions of radioactivity in PMTs. Measurements with germanium detectors showed 1.2 ± 0.3 mBq/PMT of 226Ra, less than 0.78 mBq/PMT of 228Ra, 9.1 ± 2.2 mBq/PMT of 40K, and 2.8 ± 0.2 mBq/PMT of 60Co. In this paper, the radioactive details of the developed R10789 are described together with our screening methods and the components of the PMT.
This paper describes the recent results of divertor simulation research toward the realization of the detached plasma using the end-mirror of a large tandem mirror device. The additional ion ...cyclotron range of frequency heating in the anchor-cells for higher particle flux generation significantly increases the density, which attained the highest particle flux up to 1.76 × 10
23
particles/·m
2
at the end-mirror exit. Massive gas injection (H
2
and noble gases) into the divertor simulation experimental module (D-module) was performed, and a remarkable reduction of the electron temperature on the target plate was successfully achieved associated with the strong reduction of particle and heat fluxes in D-module. Two-dimensional images of Hα emission in D-module observed with a high-speed camera showed strong emission in the upstream region and significant reduction near the target plate. These results clarified the effect of radiation cooling and formation of detached plasma due to gas injection. It is also found that Xe gas is much more effective in achieving detached plasma than Ar gas. Numerical simulation studies also have been performed toward the understanding of the cooling mechanism of divertor plasma. The above results will contribute to establishment of detached plasma control and clarification of the radiation cooling mechanism toward the development of future divertor systems.
Abstract We have established a method to measure picograms-per-gram (pg g−1) levels of 238U and 232Th in scintillation films by combining the dry ashing method and inductively coupled plasma mass ...spectrometry. Trace amounts of 238U and 232Th were measured in up to 2 g of scintillation film with almost 100% collection efficiency. This paper details the experimental procedure, including the pretreatment of the samples and labware, detection limit of the method, collection efficiencies of 238U and 232Th, and measurement of 238U and 232Th in a polyethylene naphthalate film. This method is also applicable to 238U and 232Th measurements in other low-background organic materials for rare-event search experiments.
The rough lemon pathotype of Alternaria alternata produces host-selective ACR-toxin and causes Alternaria leaf spot disease of rough lemon (Citrus jambhiri). The structure of ACR-toxin I (MW = 496) ...consists of a polyketide with an α-dihydropyrone ring in a 19-carbon polyalcohol. Genes responsible for toxin production were localized to a 1.5-Mb chromosome in the genome of the rough lemon pathotype. Sequence analysis of this chromosome revealed an 8,338-bp open reading frame, ACRTS2, that was present only in the genomes of ACR-toxin-producing isolates. ACRTS2 is predicted to encode a putative polyketide synthase of 2,513 amino acids and belongs to the fungal reducing type I polyketide synthases. Typical polyketide functional domains were identified in the predicted amino acid sequence, including β-ketoacyl synthase, acyl transferase, methyl transferase, dehydratase, β-ketoreductase, and phosphopantetheine attachment site domains. Combined use of homologous recombination-mediated gene disruption and RNA silencing allowed examination of the functional role of multiple paralogs in ACR-toxin production. ACRTS2 was found to be essential for ACR-toxin production and pathogenicity of the rough lemon pathotype of A. alternata.
Bosonic superweakly interacting massive particles (super-WIMPs) are a candidate for warm dark matter. With the absorption of such a boson by a xenon atom, these dark matter candidates would deposit ...an energy equivalent to their rest mass in the detector. This is the first direct detection experiment exploring the vector super-WIMPs in the mass range between 40 and 120 keV. With the use of 165.9 day of data, no significant excess above background was observed in the fiducial mass of 41 kg. The present limit for the vector super-WIMPs excludes the possibility that such particles constitute all of dark matter. The absence of a signal also provides the most stringent direct constraint on the coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented sensitivity was achieved exploiting the low background at a level 10(-4) kg-1 keVee-1 day-1 in the detector.
The coherent elastic neutrino-nucleus scattering (CEvNS) plays a crucial role at the final evolution of stars. The detection of it would be of importance in astroparticle physics. Among all available ...neutrino sources, galactic supernovae give the highest neutrino flux in the MeV range. Among all liquid xenon dark matter experiments, XMASS has the largest sensitive volume and light yield. The possibility to detect galactic supernova via the CEvNS-process on xenon nuclei in the current XMASS detector was investigated. The total number of events integrated in about 18 s after the explosion of a supernova 10 kpc away from the Earth was expected to be from 3.5 to 21.1, depending on the supernova model used to predict the neutrino flux, while the number of background events in the same time window was measured to be negligible. All lead to very high possibility to detect CEvNS experimentally for the first time utilizing the combination of galactic supernovae and the XMASS detector. In case of a supernova explosion as close as Betelgeuse, the total observable events can be more than ∼ 104, making it possible to distinguish different supernova models by examining the evolution of neutrino event rate in XMASS.
• Molecular activated recombination (MAR) leading to plasma detachment has been observed by additional hydrogen gas injection to the divertor simulation plasma.• Dependence of balmer line emissions ...(Hα and Hβ) on the neutral pressure indicates that the dissociative attachment process in MAR is more dominant than the ion conversion process.• The triatomic molecules would play an important role in MAR for the plasma detachment.
In the tandem mirror GAMMA 10/PDX, molecular activated recombination (MAR) leading to plasma detachment has been observed by additional hydrogen gas injection to the divertor simulation plasma (i.e. end loss plasma) which is exposed to the V-shaped target in the divertor simulation experimental module (D-module). The temperature near the corner of the V-shaped target decreased from ∼23eV to ∼2eV as the neutral pressure in the D-module increased. A clear density rollover was observed at ∼2Pa. A position of the density maximum moves to upstream of the plasma with increase in the neutral pressure and the density near the corner of the target decreases to detach the plasma from the target. After the occurrence of the density rollover, the Balmer β intensity decreases as with the density but the Balmer α intensity continues to increase, indicating the dissociative attachment process in MAR is more dominant than the ion conversion process although the rate coefficient of the former process is lower than that of the latter one, which is calculated by using a collisional radiative model. This would be caused by the MAR process related to triatomic hydrogen molecules which significantly contributed to the detachment process.
This paper describes the results of characterization of high heat and particle fluxes produced at the end-cell of the large tandem mirror GAMMA 10 and of the initial plasma-irradiation experiments. ...In the case of ICRF plasmas, the heat flux of 0.8MW/m2 and the particle flux of 4×1022/m2s were achieved at the end-mirror exit. The heat flux increases with the ICRF power and has a linear relationship with the stored energy. Direct ion energy analysis clarified that the parallel ion temperature can be controlled from 100eV to 400eV by changing the ICRF power. Additional plasma heating using another ICRF system in the anchor-cell significantly increases the particle flux, which gives a clear prospect of generating the higher particle flux by applying additional ICRF heating in the neighboring cells. The initial results of the plasma–gas–material interactions on a new V-shaped tungsten target were also reported.
The working principles of the photoalignment induced by photochromic molecules depend crucially on the liquid crystals (LC) systems employed. A comprehensive examination of the photoalignment of LC ...systems is presented.
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