Showing papers by "Ken-Ichi Fushimi published in 2021"
TL;DR: The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter as discussed by the authors, and the optimized methods were combined to reduce various radioactive impurities.
Abstract: The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter. The optimized methods were combined to reduce various radioactive impurities. The $^{40}$K was effectively reduced by the re-crystallization method. The progenies of the decay chains of uranium and thorium were reduced by appropriate resins. The concentration of natural potassium in NaI(Tl) crystal was reduced down to 20 ppb. Concentrations of alpha-ray emitters were successfully reduced by appropriate selection of resin. The present concentration of thorium series and 226Ra were $1.2 \pm1.4$ $\mu$Bq/kg and $13\pm4$ $\mu$Bq/kg, respectively. No significant excess in the concentration of $^{210}$Pb was obtained, and the upper limit was 5.7 $\mu$Bq/kg at 90% C. L. The achieved level of radiopurity of NaI(Tl) crystals makes construction of a dark matter detector possible.
14 citations
TL;DR: The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter as discussed by the authors, and the optimized methods were combined to reduce various radioactive impurities.
Abstract: The highly radiopure NaI(Tl) was developed to search for particle candidates of dark matter. The optimized methods were combined to reduce various radioactive impurities. The $^{40}$K was effectively reduced by the re-crystallization method. The progenies of the decay chains of uranium and thorium were reduced by appropriate resins. The concentration of natural potassium in NaI(Tl) crystal was reduced down to 20 ppb. Concentrations of alpha-ray emitters were successfully reduced by appropriate selection of resin. The present concentration of thorium series and 226Ra were $1.2 \pm1.4$ $\mu$Bq/kg and $13\pm4$ $\mu$Bq/kg, respectively. No significant excess in the concentration of $^{210}$Pb was obtained, and the upper limit was 5.7 $\mu$Bq/kg at 90% C. L. The achieved level of radiopurity of NaI(Tl) crystals makes construction of a dark matter detector possible.
12 citations
TL;DR: In this paper, a CANDLES-III system was developed to study the neutrino-less double beta (0$
u\beta\beta$) decay of $^{48}$Ca.
Abstract: We developed a CANDLES-III system to study the neutrino-less double beta (0$
u\beta\beta$) decay of $^{48}$Ca. The proposed system employs 96 CaF$_{2}$ scintillation crystals (305 kg) with natural Ca ($^{\rm nat.}$Ca) isotope which corresponds 350\,g of $^{48}$Ca. External backgrounds were rejected using a 4$\pi$ active shield of a liquid scintillator surrounding the CaF$_2$ crystals. The internal backgrounds caused by the radioactive impurities within the CaF$_2$ crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4\,days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF$_{2}$ crystals and the rate of high energy $\gamma$-rays caused by the (n, $\gamma$) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10$^{-3}$ events/keV/yr/(kg of $^{\rm nat.}$Ca), in the 0$
u\beta\beta$ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0$
u\beta\beta$ decay in a low background condition using a detector with a Ca isotope, in which the Ca present was not enriched, in a scale of hundreds of kg. The $^{48}$Ca isotope has a high potential for use in 0$
u\beta\beta$ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.
12 citations
11 Jan 2021-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, a novel calibration system based on γ-ray emission by neutron capture on 28Si, 56Fe, and 58Ni nuclei was developed for CANDLES up to 9 MeV.
Abstract: Calcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double-beta decay of 48Ca using a Ca F 2 scintillator array. A high Q-value of 48Ca at 4268 keV enabled us to achieve low background, however, at the same time it causes difficulties in calibrating the detector’s Q-value region because of the absence of a standard high-energy γ -ray source. Therefore, we have developed a novel calibration system based on γ -ray emission by neutron capture on 28Si, 56Fe, and 58Ni nuclei. In this paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV.
8 citations
TL;DR: In this article, the authors performed a search for event bursts in the XMASS-I detector associated with 11 gravitational-wave events detected during LIGO/Virgo's O1 and O2 periods.
4 citations
University of Tokyo1, Osaka University2, University of Tokushima3, Kyoto University4, Lawrence Berkeley National Laboratory5, Massachusetts Institute of Technology6, University of Tennessee7, University of Washington8, University of North Carolina at Chapel Hill9, North Carolina Central University10, Duke University11, University of Amsterdam12, Boston University13, Virginia Tech14
TL;DR: Abe et al. as mentioned in this paper presented the results of a search for MeV-scale electron antineutrino events in KamLAND coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs.
Abstract: Author(s): Abe, S; Asami, S; Gando, A; Gando, Y; Gima, T; Goto, A; Hachiya, T; Hata, K; Hayashida, S; Hosokawa, K; Ichimura, K; Ieki, S; Ikeda, H; Inoue, K; Ishidoshiro, K; Kamei, Y; Kawada, N; Kishimoto, Y; Kinoshita, T; Koga, M; Maemura, N; Mitsui, T; Miyake, H; Nakamura, K; Nakamura, K; Nakamura, R; Ozaki, H; Sakai, T; Sambonsugi, H; Shimizu, I; Shirai, J; Shiraishi, K; Suzuki, A; Suzuki, Y; Takeuchi, A; Tamae, K; Ueshima, K; Wada, Y; Watanabe, H; Yoshida, Y; Obara, S; Kozlov, A; Chernyak, D; Takemoto, Y; Yoshida, S; Umehara, S; Fushimi, K; Ichikawa, AK; Nakamura, KZ; Yoshida, M; Berger, BE; Fujikawa, BK; Learned, JG; Maricic, J; Axani, SN; Winslow, LA; Fu, Z; Ouellet, J; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; Li, A; Detwiler, JA; Enomoto, S; Decowski, MP; Grant, C; O'Donnell, T; Dell'Oro, S | Abstract: We present the results of a search for MeV-scale electron antineutrino events in KamLAND coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs. We find no significant coincident signals within a 500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between 108 and 1013 cm-2 for neutrino energies in the energy range of 1.8-111 MeV.
3 citations
TL;DR: In this article, the authors used photon counting to obtain the number of photo-electrons in each PMT to avoid photoelectron signal overlapping probability, which severely degrades the resolution.
Abstract: In a neutrinoless double-beta decay ( $0
u \beta \beta $ ) experiment, energy resolution is important to distinguish between $0
u \beta \beta $ and background events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the $0
u \beta \beta $ of 48Ca using a CaF2 scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. At the $Q$ value of 48Ca, the current energy resolution (2.6%) exceeds the ideal statistical fluctuation of the number of photoelectrons (1.6%). Because of CaF2’s long decay constant of 1000 ns, a signal integration within 4000 ns is used to calculate the energy. The baseline fluctuation ( $\sigma _{\mathrm{ baseline}}$ ) is accumulated in the signal integration, thus degrading the energy resolution. This article studies $\sigma _{\mathrm{ baseline}}$ in the CANDLES detector, which severely degrades the resolution by 1% at the $Q$ value of 48Ca. To avoid $\sigma _{\mathrm{ baseline}}$ , photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. “Partial photon counting” reduces $\sigma _{\mathrm{ baseline}}$ and minimizes photoelectron loss. We obtain improved energy resolutions of 4.5%–4.0% at 1460.8 keV ( $\gamma $ -ray of 40K) and 3.3%–2.9% at 2614.5 keV ( $\gamma $ -ray of 208Tl). The energy resolution at the $Q$ value is estimated to be improved from 2.6% to 2.2%, and the detector sensitivity for the $0
u \beta \beta $ half-life of 48Ca can be improved by 1.09 times.
1 citations
Posted Content•
TL;DR: In this paper, a search for neutrinos in coincidence with solar flares from the GOES database was performed on a 10.8kton-year exposure of KamLAND collected from 2002 to 2019.
Abstract: We report the result of a search for neutrinos in coincidence with solar
flares from the GOES flare database. The search was performed on a 10.8
kton-year exposure of KamLAND collected from 2002 to 2019. We found no
statistical excess of neutrinos and established 90\% confidence level upper
limits of $8.4 \times 10^7$\,cm$^{-2}$ ($3.0 \times 10^{9}$\,cm$^{-2}$) on
electron anti-neutrino (electron neutrino) fluence at 20\,MeV normalized to the
X12 flare, assuming that the neutrino fluence is proportional to the X-ray
intensity. The 90\% C.L. upper limits from this work exclude the entire region
of parameter space associated with the Homestake event excess for the large
solar flare in 1991.
TL;DR: The inner balloon (IB) as mentioned in this paper is a balloon made of thin, transparent, low-radioactivity film that is used in the KamLAND-Zen 800 experiment to minimize the background from cosmogenic muon-spallation products.
Abstract: The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta decay of $^{136}$Xe by using $^{136}$Xe-loaded liquid scintillator. The liquid scintillator is enclosed inside a balloon made of thin, transparent, low-radioactivity film that we call Inner Balloon (IB). The IB, apart from guaranteeing the liquid containment, also allows to minimize the background from cosmogenic muon-spallation products and $^{8}$B solar neutrinos. Indeed these events could contribute to the total counts in the region of interest around the Q-value of the double-beta decay of $^{136}$Xe. In this paper, we present an overview of the IB and describe the various steps of its commissioning minimizing the radioactive contaminations, from the material selection, to the fabrication of the balloon and its installation inside the KamLAND detector. Finally, we show the impact of the IB on the KamLAND background as measured by the KamLAND detector itself.
Posted Content•
TL;DR: In this article, the authors developed a highly radiopure NaI(Tl) crystal to search for dark matter, and the best combination of the purification methods was developed, resulting $^{\mathrm{nat}}$K and $^{210}$Pb were less than 20 ppb and 5.7 pb, respectively.
Abstract: A dark matter search project needs and extremely low background radiation detector since the expected event rate of dark matter is less than a few events in one year in one tonne of the detector mass. The authors developed a highly radiopure NaI(Tl) crystal to search for dark matter. The best combination of the purification methods was developed, resulting $^{\mathrm{nat}}$K and $^{210}$Pb were less than 20 ppb and 5.7 $\mu$Bq/kg, respectively.
The authors will construct a large volume detector system with high-purity NaI(Tl) crystals. The design and the performance of the prototype detector module will be reported in this article.