Development of ultra-pure gadolinium sulfate for the Super-Kamiokande gadolinium project

Journal Article · Mon Dec 12 00:00:00 UTC 2022 · Progress of Theoretical and Experimental Physics

DOI: https://doi.org/10.1093/ptep/ptac170 · OSTI ID:2424433

Hosokawa, K. ^[1]; Ikeda, M. ^[1]; Okada, T. ^[1]; Sekiya, H. ^[2]; Fernández, P. ^[3]; Labarga, L. ^[3]; Bandac, I. ^[4]; Perez, J. ^[4]; Ito, S. ^[5]; Harada, M. ^[6]; Koshio, Y. ^[7]; Thiesse, M. D. ^[8]; Thompson, L. F. ^[8]; Scovell, P. R. ^[9]; Meehan, E. ^[9]; Ichimura, K. ^[10]; Kishimoto, Y. ^[10]; Nakajima, Y. ^[11]; Vagins, M. R. ^[12]; Ito, H. ^[13] ; Takaku, Y. ^[14]; Tanaka, Y. ^[15]; Yamaguchi, Y. ^[15]

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1. University of Tokyo, Gifu (Japan)
2. University of Tokyo, Gifu (Japan); University of Tokyo, Chiba (Japan)
3. University Autonoma Madrid (Spain)
4. Laboratorio Subterraneo de Canfranc, Huesca (Spain)
5. High Energy Accelerator Research Organization (KEK), Ibaraki (Japan)
6. Okayama University (Japan)
7. University of Tokyo, Chiba (Japan); Okayama University (Japan)
8. University of Sheffield (United Kingdom)
9. Boulby Underground Laboratory (United Kingdom)
10. Tohoku University Research Center for Neutrino Science, Miyagi (Japan)
11. University of Tokyo (Japan)
12. University of Tokyo, Chiba (Japan); University of California, Irvine, CA (United States)
13. Tokyo University of Science, Chiba (Japan)
14. University of Tsukuba, Ibaraki (Japan)
15. Nippon Yttrium Co., Ltd., Fukuoka (Japan)

This paper reports the development and detailed properties of about 13 metric tons of gadolinium sulfate octahydrate, Gd₂(SO₄)₃ • 8H₂O⁠, which has been dissolved into Super-Kamiokande (SK) in the summer of 2020. We evaluate the impact of radioactive impurities in Gd₂(SO₄)₃ • 8H₂O 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 Gd₂(SO₄)₃ • 8H₂O⁠. In order to produce ultra-high-purity Gd₂(SO₄)₃ • 8H₂O, 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 Gd₂(SO₄)₃ • 8H₂O 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 Gd₂(SO₄)₃ • 8H₂O 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.

• Research Organization: University of California, Irvine, CA (United States)
• Sponsoring Organization: USDOE
• OSTI ID: 2424433
• Journal Information: Progress of Theoretical and Experimental Physics, Journal Name: Progress of Theoretical and Experimental Physics Journal Issue: 1 Vol. 2023; ISSN 2050-3911
• Publisher: Physical Society of JapanCopyright Statement
• Country of Publication: United States
• Language: English