Radioassay and Purification for Experiments at Y2L and Yemilab in - PowerPoint PPT Presentation

Radioassay and Purification for Experiments at Y2L and Yemilab in Korea Moo-Hyun Lee Center for underground Physics, Institute for Basic Science (IBS), Korea 2019. 09. 09 TAUP 2019 @ TIIC, Toyama, Japan

Yangyang underground laboratory (Y2L) & CUP Center for Underground Physics (Upper Dam) IBS (Institute for Basic Science) 2.5 hour Y2L YangYang Pumped driving Seoul Storage Power Plant 1000m 3.3 hour driving 700m CUP/IBS Since Daejeon (Power Plant) 2014 A5: Since COSINE, AMoRE (Lower Dam) 2003 HPGe array, Alpha A6: COSINE-100 (WIMP Dark Matter) *DM12 KIMS-CsI & HPGe AMoRE (0 !"" Decay) *Neutrino17 Minimum depth : 700 m / Access to the lab by car (~2km) Radioassay and purification in Korea, Moo-Hyun Lee (IBS)

3 AMoRE Experiment: 0 !"" decay search l Sizable background case: Q ## =3.03 MeV Detection Isotopic Detector Mass Efficiency Abundance 0 !"" 2 !"" Measurement a Mt n 0 = e T (exp) (ln 2 ) N time 1 / 2 A D A b E Energy Resolution Sensitivity Atomic Background rate to half-life mass of 0 νββ AMoRE-II 200kg l “Zero” background case: zero background non-zero When b is ~ O(1), background AMoRE-I a n = e 5kg 0 T (exp) (ln 2 ) N Mt 1 / 2 A A AMoRE is aiming for zero background. Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

AMoRE Parameters 4 ¨ Crystals: 40 Ca 100 MoO 4 (CMO) or XMO (X: Li, Na, or Pb) ¤ 100 Mo enriched: > 95% ¤ 48 Ca depleted: < 0.001% (N.A. of 48 Ca:0.187%) CMO LiMO PbMO ¨ Low temperature detector: 10 – 30 mK ¨ Energy resolution: ~5 keV @ 3MeV ¨ Excellent PSD The AMoRE configuration and plan Pilot Phase I Phase II Mass (Crystal) 1.9 kg CMO 6 kg (CMO + LMO) 200 kg XMO (X: Li, Na, Pb) BKG [keV . kg . year] -1 <10 -2 <10 -3 <10 -4 T 1/2 Sensitivity [years] ~10 24 ~10 25 ~8 × 10 26 <m bb > Sensitivity [meV] 400 - 700 100 - 300 13 - 25 Location Y2L (700 m depth) Yemi Lab (1100m depth) Schedule 2015 - 8 2019 - 2021 2021 - Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Identify critical radioactivity 5 q Go through all known nuclei decaying ! with Q !! > 3.02MeV in NNDC database. q 110m Ag (3.0105 MeV) doesn’t contribute for Mo experiment. q Cosmogenic excitation is negligible after 1 year at underground. q Only Th and U natural radio-activities are critical for Q> 3.02MeV. → Great advantage to run high Q-value nuclei ! Element Decay T 1/2 Q (MeV) Mother Chain Comment 26 Al 7.4x10 5 y EC 4.004 N/A Long lifetime 56 Co EC 0.21y 4.567 N/A Short lifetime 88 Y 88 Zr (0.23 y) EC 0.29y 3.623 Short lifetime 106 Rh 106 Ru(1.02y) B- 30s 4.004 126 Sb 126 Sn(2.3x10 5 y) B- 12.5d 3.670 Long lifetime 146 Eu 146 Gd (0.13 y) EC 4.61d 3.878 Short lifetime 208 Tl 228 Th (1.91 y) 232 Th B- 3.05m 4.999 Main 209 Tl 233 U(159200y) 233 U B- 2.16m 3.970 2.1% branching 210 Tl 226 Ra(1600y) 238 U B- 1.3m 5.482 0.02% branching 214 Bi 226 Ra(1600y) 238 U B- 19.9m 3.269 Main Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

COSINE-100 instrument for WIMP DM search 6 Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

COSINE-100 NaI(Tl) crystal detector 7 q 8 ultra low-background NaI(Tl) crystals with a mass of 106 kg in total q U/Th/K levels are less than DAMA, but total alphas ( 210 Pb) are higher than DAMA. q Higher light yield (15 p.e/keV) than DAMA q Can make the threshold lower easily q Total background level is 2-3 times that of DAMA. Mass Alpha rate 40 K 238 U 232 Th Light yield Crystal Powder (kg) (mBq/kg) (ppb) (ppt) (ppt) (p.e./keV) 8.3 AS-B 3.20 ± 0.08 43.4 ± 13.7 < 0.02 1.31 ± 0.35 14.88 ± 1.49 Crystal 1 2.06 ± 0.06 82.7 ± 12.7 14.61 ± 1.45 9.2 AS-C < 0.12 < 0.63 Crystal 2 9.2 AS-WS � 0.76 ± 0.02 41.1 ± 6.8 < 0.04 0.44 ± 0.19 15.50 ± 1.64 Crystal 3 18.0 AS-WS � 0.74 ± 0.02 39.5 ± 8.3 < 0.3 14.86 ± 1.50 Crystal 4 2.06 ± 0.05 86.8 ± 10.8 2.35 ± 0.31 7.33 ± 0.70 Crystal 5 18.0 AS-C 12.5 AS-WS � 1.52 ± 0.04 12.2 ± 4.5 < 0.018 0.56 ± 0.19 14.56 ± 1.45 Crystal 6 1.54 ± 0.04 18.8 ± 5.3 13.97 ± 1.41 12.5 AS-WS � < 0.6 Crystal 7 18.3 AS-C 2.05 ± 0.05 56.15 ± 8.1 < 1.4 3.50 ± 0.33 Crystal 8 < 0.5 < 20 0.7 - 10 0.5 – 7.5 5.5 – 7.5 DAMA Eur. Phys. J. C. 78 107 (2018) Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

COSINE-100 Background Modeling 8 q Detector simulation based on GEANT4 well reproduces measured background spectra (4 channels for each crystal, single: 6 - 2000 keV, multiple: 2 - 2000 keV). q Main background in low energy region − Contamination of crystals from 40 K/U/Th multiple hit − Cosmogenic activation (mostly 3 H) − 210 Pb on crystal surface Eur. Phys. J. C. 78 490 (2018) single hit single hit Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Low Background Measurements at Y2L 9 HPGe Array Alpha counter ¨ 2 HPGe detectors (2 Coax) A5 ¨ 1 Array with 14 HPGe detectors ¨ Alpha ionization counter ~700 m deep A5 A6 HPGe (CC2) HPGe (CC1) Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Two single HPGe detectors: Screening of raw materials 10 CC1: 100% HPGe CANBERRA Dedicated shielding: ‒ Top & bottom 10 cm Pb + 10 cm Cu (inner) ‒ Side 15 cm Pb + 10 cm Cu (inner) ‒ 5 cm thick ancient Pb closer to the detector Count rates of background (50 − 4000 keV) 8.1 mHz (2015), 7.9 mHz (2018), 7.8 mHz (2019) CC2: 100% HPGe CANBERRA Dedicated shielding: ‒ General Pb (10 cm) + Goslar Pb (10 cm) + Cu (10 cm) Count rates of background (50 − 3500 keV) 9.5 mHz (2017), 7.9 mHz (2018), 6.8 mHz (2019) Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

HPGe measurement example (Iridium crucible) 11 CMD246 IRIDIUM CRUCIBLE 190305 Mass: 1.627 kg, Meas.day: 21 day @CC2 q Iridium Crucible for Mo based crystal growing q Mass : 1627.4 g q Geometry: 100 (IR) x 100 (H) x 2(T) mm q BKG : CC1 large volume (14 days) 226 Ra( 238 U) 40 K 228 Ac 228 Th 17.44 ± 1.54 mBq/kg < 7.01 mBq/kg < 4.31 mBq/kg 5.04 ± 1.26 mBq/kg 192 Ir 5.24 +/- 0.26 Bq/kg Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

CC1 & CC2 measurements records 12 CC1 Year Total AMoRE COSINE HPGe LZ Y2L Yemi R&D 2017 15 9 2 3 1 2018 17 10 5 1 1 2019 6 4 1 1 CC2 Year Total AMoRE COSINE HPGe LZ Y2L Yemi R&D 2017 21 7 11 3 2018 23 15 5 2 1 2019 11 7 1 2 1 § Test duration of each sample is for 1-3 weeks depending on its purity. § HPGe had array materials, Ta and ThO 2 samples measured § LZ for 8 inch PMTs § Y2L and Yemilab for rocks and shotcrete materials Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Array of 14 HPGe detectors 13 § Developed in collaboration with CANBERRA. Operation from March 2017. § 2 ARRAYS placed one above the other with 7 HPGe (70% relative efficiency) each, total 980% with 14 HPGe detectors § Low background copper for endcap & holder. § O-rings were screened from more than 20 samples. § The sensitivity can be improved thanks to coincidence measurements. § Raw materials screening such as Mo-100 powder (AMoRE) or copper. Rare decay search like 180m Ta rare beta decay § Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Mo-100 powder (ECP) for AMoRE-II 14 Lot# Delivery@Y2L #1(3172) 3/9/16 Top Array #2(3328) 3434 12/28/16 3497 10/12/17 3535 100 kg delivered 3589 2/7/18 out of 110 kg Mo-100 powder bags 3649 5/29/18 9771 g 2 nd shipment 3675 8/14/18 3741 2/13/19 3803 5/31/19 3824 8/20/19 Bottom Array HPGe Array meas. (9/13 – 11/28/2017) § 226 Ra chain ( 238 U) < 1.4 mBq/kg § 228 Th chain ( 232 Th) = 0.55 ± 0.15 mBq/kg 88 Y (cosmogenic) = 84 ± 18 ! Bq/kg § 1919 h data (1578 h BKG) with a total of 9618 g sample. Last delivery ~Sep. 2019 Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Alpha Counter 15 l An extremely sensitive alpha counter (argon gas chamber) is purchased from XIA and installed at Y2L in summer 2015. l Background rate : ~ 0.0001 alphas/cm 2 /hour. l Essential to study Pb-210 surface contamination for DM experiment. Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

How deep can Pb-210 penetrate in the NaI(Tl)? 16 CUP Preliminary CUP Preliminary q Po-210 depth is estimated at around 1.2+/-1.0 µ m (stat. only) in the NaI(Tl) crystal. More accurate estimation requires to understand how particle diffusion happens in the surface. Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09

Ultra-sensitive Radon detector 17 § Hamamatsu silicon PIN § Hamamatsu charge photodiode (S3204-9) 18 sensitive amplifier Í 18 mm 2 (H4083) § HV divider circuit § Volume = 70 L § High Voltage = - 1,000 V § Bias = 30 V § Stainless steel with electro-polished inside surfaces § Shaping amplifier with Í 12 gain § 12 bit 25 MS/s FADC Radioassay and purification in Korea, Moo-Hyun Lee (IBS) TAUP2019@Toyama, 2019-09-09