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PICOLON dark matter search ~ Development of highly radiopure NaI(Tl) scintillator

This project aims to develop a highly radiopure NaI(Tl) scintillator for the PICOLON Collaboration in order to achieve a background level of ~1/day/keV/kg at 1 keVee. The purification of NaI(Tl) powder, selection of cation exchange resin, and optimization of purification conditions are among the key focus areas.

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PICOLON dark matter search ~ Development of highly radiopure NaI(Tl) scintillator

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  1. PICOLON dark matter search~ Development of highly radiopure NaI(Tl) scintillator K.FUshimi for PICOLON collaboration TAUP2019 TOYAMA 2019/Sep/11

  2. 1. Why NaI(Tl) ? • Only NaI(Tl) scintillator shows an appreciable signal. R.Bernabei, CSLNGS, March 26, 2018 250 kg NaI(Tl) BG = 1 dru at 2 keVee TAUP2019 TOYAMA 2019/Sep/11

  3. 1. Recently.... COSINE-100 (106 kg) arXiv:1903.10098v1 [astro-ph.IM] • BG = 2.7 /day/keV/kg @ 2-6 keVee • Amplitude = 0.0092±0.0067 /day/keV/kg • Less statistic accuracy. TAUP2019 TOYAMA 2019/Sep/11

  4. Need verification by NaI(Tl) scintillator TAUP2019 TOYAMA 2019/Sep/11

  5. PICOLON Project Goal of BG level ~ 1 /day/keV/kg at 1 keVee Total mass 56 kg  250 kg  1 ton • Pure Inorganic Crystal Observatory for LOw-energy Neutr(al)ino Funded! KamLAND-PICO 1000 kg NaI(Tl) ~2030 SCALE UP 250 kg NaI(Tl) ~2025 54 kg NaI(Tl) ~2020 Funded! 35 MJPY TAUP2019 TOYAMA 2019/Sep/11

  6. Status of NaI(Tl) purification(~April 2019) TAUP2019 TOYAMA 2019/Sep/11

  7. Development of high purity NaI(Tl) : PICO-LON • Pure Inorganic Crystal Observatory for LOw-background Neutralino • Purification of NaI powder • Selection of cation exchange resin. • Pb reduction by resin. • Optimization of purification condition. • Low BG measurement • Selection of surrounding materials. • Measurement in Kamioka Underground Laboratory. TAUP2019 TOYAMA 2019/Sep/11

  8. Normal NaI(Tl) : A few mBq of U,Th TAUP2019 TOYAMA 2019/Sep/11

  9. Further purification of crucible TAUP2019 TOYAMA 2019/Sep/11

  10. K.Fushimi et al., arXiv:1407.3542, Proceedings of the 26th Workshop on Radiation Detectors and Their Uses, KEK-Proc1225008, (2012) p122 Ingot26 • Successful reduction of 210Pb by resin. • Problem of reproducibility TAUP2019 TOYAMA 2019/Sep/11

  11. β ray from 40K  Contamination in NaI(Tl) crystal. New Measurement (↑81keV， 356keV↑) 133Baγ 40Kγ (1460keV) TAUP2019 TOYAMA 2019/Sep/11

  12. 40K removal by re-crystalization Purified NaI powder 40K is in water. TAUP2019 TOYAMA 2019/Sep/11

  13. Reduction of 40K was established! Ingot 68: 120 ppb natK Ingot 73: <20 ppb natK TAUP2019 TOYAMA 2019/Sep/11

  14. BG status of Ingot #76(Detail by a poster by Kanemitsu #371) 125I 126I EVENTS/keV/day/kg 210Pb Still high BG of alpha rays. ~1000 μBq/kg (46.5 keV gamma from 210Pb.) ~560 μBq/kg (Alpha ray from 210Po.) TAUP2019 TOYAMA 2019/Sep/11

  15. Alpha ray trend Fit with 210Po half-life:: Final activity = 560 μBq/kg TAUP2019 TOYAMA 2019/Sep/11

  16. Status of NaI(Tl) purification(~April 2019) Factory moved. TAUP2019 TOYAMA 2019/Sep/11

  17. Possible origins of 210Pb in NaI(Tl) TAUP2019 TOYAMA 2019/Sep/11

  18. Prospects TAUP2019 TOYAMA 2019/Sep/11

  19. For the significant verification. TAUP2019 TOYAMA 2019/Sep/11

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