1 / 26

A CsI(Tl) Dark Matter Search Experiment - KIMS -

A CsI(Tl) Dark Matter Search Experiment - KIMS -. Korean Invisible Mass Search. Yeongduk Kim Sejong University, Seoul, Korea IDM 2002 meeting, 2002. Sep 5. Collaborators. Seoul National Univ. : J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*, T.Y.Kim ,

nellie
Download Presentation

A CsI(Tl) Dark Matter Search Experiment - KIMS -

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A CsI(Tl) Dark Matter Search Experiment- KIMS - Korean Invisible Mass Search Yeongduk Kim Sejong University, Seoul, Korea IDM 2002 meeting, 2002. Sep5

  2. Collaborators Seoul National Univ.: J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*,T.Y.Kim, H.S. Lee, S.E. Lee, H..Park, H.Y.Yang, M.S.Yang Sejong Univ. : W.K.Kang, J.I. Lee, D.S.Lim, Y.D.Kim, Yonsei Univ. : J.Hwang, H.J.Kim, Y.J.Kwon Iwha Womans Univ. : I.S.Han, E.K.Lee, I.H. Park SeongKyunKwan Univ. : I.Yu Chonbuk National Univ. : S.Y.Choi KAIST : P.Ko Univ. of Maryland :M.H.Lee, E.S.Seo National Taiwan Univ., : H.B.Li, C.H.Tang, M.Z.Wang Academia Cinica : W.P.Lai, H.T. Wong Inst. Of High Energy Physics : J.Li, Y.Liu, Q.Yue Inst. Of Atomic Energy : B.Xin, Z.Y.Zhou Tsinghua University : J. Zhu * PI

  3. Outline • CsI(Tl) crystals • Underground site • Studies on background reduction • Perspectives • Summary

  4. Why CsI(Tl) Crystal ? Advantage High light yield ~50,000/MeV Pulse shape discrimination Easy fabrication and handling High mass number(both Cs and I) SI + SD CsI(Tl) NaI(Tl) Density(g/cm3) 4.53 3.67 Decay Time(ns) ~1000 ~230 Peak emission(nm) 550 415 Hygroscopicity slight strong Disadvantages Emission spectra does not match with normal bi-alkali PMT 137Cs(t1/2 ~30y) ,134Cs(t1/2 ~2y) may be problematic

  5. Low energy signal with CsI(Tl) 3” Green Extended RbCs PMT (Electron Tubes) Digital Oscilloscope with 10ns bin Large crystal (7x7x30cm) : ~ 4.5 p.e./keV Small crystal(3x3x3cm) : ~ 6 p.e./keV

  6. Response of CsI(Tl) with elastically scattered neutron • CsI(Na) has spurious events due to surface effect • 2 keV threshold  ~ 10 keV recoil energy

  7. Pulse shape discrimination at ~ keV energy • Nuclear recoil vs gamma events • Mean time for each events for each photoelectrons in an event 4<E<10 keV

  8. cut B S NaI(Tl) S B CsI(Tl) Comparison of PSD power Ideal detector  ~ 1,  ~ 0 K << 1

  9. Underground Site • Location : minimum 350 m underground Access tunnel(1.4km) 350m Laboratory Power plant

  10. Background of CsI(Tl) • 137Cs (artificial) • 134Cs (artificial+133Cs(n,gamma)) • 87Rb (natural) Single Crystal (~10 kg) background @ ~10keV 87Rb0.63 cpd/1ppb HR ICP-MASS 137Cs0.35 cpd/1mBq/kg HPGe 134Cs 0.07 cpd/1mBq/kg “ Pollucite(raw material for Cs) contains < 8 mBq/kg of 137Cs

  11. Crystals w/o selection of CsI powder (1) 137Cs Dominating crystal 8.9 kg day data Geant 4 Simulation 137Cs 155mBq/kg 134Cs ~35mBq/kg 87Rb 3.9 ppb (ICP-MASS)

  12. Crystals w/o selection of CsI powder (2) 87Rb Dominating crystal CsI(Tl) from IHEP(China) 137Cs 13.3mBq/kg 134Cs 54.2 mBq/kg 87Rb 203 ppb (ICP-MASS)

  13. Selection of CsI powder from various vendors Crystals CsOH CsNO3 CsMnO4 ~ 3mBq/kg CsI Powders Small samples 137Cs ~14mBq/kg Rb ~ 21 ppb Chemetall Selected 137Cs 87Rb

  14. Crystals with selection of CsI powder 1st Demonstration of Reducing Bacground of CsI(Tl) by selecting powder. Should reduce further. Powder  Crystal 137Cs 15.5 ± 2.619.8 ±2.5 mBq/kg 134Cs 27.4 ± 4.634.0 ± 4.4 87Rb 20.0 ppb 23.2 (?) BG(~10 keV) 20.0 cpd 21 cpd

  15. Water Samples A large amount of water used for extraction Of Cs (Chemetall) Water samples with HPGe –Precipitation with AMP (Ammonium Molybdophosphate) 137Cs(“Normal water”) >> 137Cs(“Purified”) ~ 20 times “Purified” “Normal” Water is main source ! “Ultra-pure”

  16. CsI powder with “Purified” water • CsI powder with only “purified” water in a production scale. CsI powder Crystal “Normal” water  15.5 ±2.6  7cpd (5.4 cpd expected) “Purified” water  5.3 ± 1.0  2.4 cpd(Expected) • Factor 3 reduction of 137Cs with “Purified” water

  17. Rb reduction by Recrystallization • CsI solubility in water is very high. • Recrystallization is done at slightly lower temperature from saturation point. • 20 ppb powder  ~ 1 ppb (< 1cpd) Crystal growing by Bridgmann reduced Rb by about 25%

  18. P P C C Summary of Internal Background Reduction W Crystals W/O Selection Purified Water Normal Water

  19. External background • Cosmic rays : ~ 10-4 relative to the sea level • The rock composition (ICP-MASS) • 238U ~ 4.8 ppm, 232Th ~ 6 ppm, 40K ~ 4 ppm • With a shielding of 15cm Pb(Boliden) + 10cm Cu(OFHC) •  Can be controlled < 0.005 cpd • based a MC simulation study (GEANT4)

  20. Neutron Background at underground BC501A liquid scintillator Neutron Flux ~ 4x10-5 /cm2/sec Mainly from (alpha,n) reaction GEANT4 simulation  Can be controlled <0.001 cpd 30cm LSC (Outside Shielding) + 20cm LSC(Inside Shielding)

  21. Shielding Structure Cosmic Muon Veto

  22. Neutron detector inside Copper shielding Po-Be neutron source 20cm BC501A  Neutron tagging efficiency > 75%

  23. Sensitivity (Spin-Independent) After 1 year data taking with 100 kg CsI(Tl) 2 keV threshold 3 count/(kev kg day) CDMS Limit DAMA

  24. Summary • Extensive R&D on CsI(Tl) crystal has been carried out • Pulse shape discrimination from -rays • Main source of 137Cs contamination due to impure water. • Rb reduction down to ~1ppb achieved. •  < 5cpd from internal background. • Shielding capable of 250 kg of CsI(Tl) under construction. • Environmental background : small enough • Large (n,gamma) separable LSC inside shielding is tested. • Perspectives • ~100 kg CsI(Tl) crystal within 1 year • 1 year data taking will cover DAMA region

More Related