1 / 25

CsI crystal for WIMP Search

CsI crystal for WIMP Search. For the KIMS Collaboration. Korea Invisible Mass Search. Seoul National Univ. : J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*, T.Y.Kim, H.S.Lee, H.Park I.H.Park, E.Won, H.S.Won, H.Y.Yang, M.S.Yang

brock
Download Presentation

CsI crystal for WIMP Search

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. CsI crystal for WIMP Search For the KIMS Collaboration Korea Invisible Mass Search Seoul National Univ.: J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*, T.Y.Kim, H.S.Lee, H.Park I.H.Park, E.Won, H.S.Won, 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, J.H.Lee, Y.J.Kwon, Iwha Womans Univ. : I.S.Hahn, E.K.Lee SeongKyunKwan Univ. : I.S.Cho, D.H.Choi, S.H.Noh, I.Yu Chonbuk National Univ. : S.Y.ChoiKAIST : 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, Tsing Hua University : J.J.Zhu Sun Kee Kim Seoul National University

  2. Brief History of KIMS • 1997 Summer : First discussion on WIMP search in Korea • 1997 Fall : Started R&D on CsI(Tl) for WIMP search • 1998 Summer : Demonstrated that CsI(Tl) can be used • as a WIMP detector - presented at ICHEP98 • 1999 Spring : Started background measurement at Cheongphyung • 2000 Summer : Project funded, KIMS collaboration formed • 2001 August : TDR, Project Review Committee

  3. CsI(Tl) Crystal Advantages High light yield ~50,000/MeV Pulse shape discrimination Easy fabrication and handling High mass number(both Cs and I) CsI(Tl) NaI(Tl) Density(g/cm3) 4.53 3.67 Decay Time(ns) ~1050 ~230 Peak emission(nm) 550 415 Hygroscopicity slight strong Disadvantages Emission spectra does not match with normal bialkali PMT => effectively reduce light yield 137Cs(t1/2 ~30y) ,134Cs(t1/2 ~2y) may be problematic

  4. Photoelectron yield RbCs(green extended) PMT(D726UK) 70% larger p.e. than the normal bialkali PMT Full size crystal (7x7x30) : ~ 4 p.e./keV Small crystal(3x3x3) : 5~7 p.e./keV

  5. Neutron Beam Test KIGAM(Korea Institute of Geology and Material) 3.2 MeV p : 3H(p,n)3He  2.62 MeV n

  6. Quenching factor n n QF = Emeasured / Erecoil

  7. Pulse Shape

  8. Mean Time

  9. Quality factor cut B S S B Ideal detector  ~ 1,  ~ 0 K << 1

  10. CsI(Na) 1st measurement of CsI(Na)

  11. Underground Lab. at Cheongpyung Storage Water Power Plant ~1000 mwe ~ 2 hours from SNU Homyung Mt.(虎鳴山) Reservoir Access tunnel(1.4km) 350m Pukhan River(北漢江) Laboratory Power plant

  12. External background • Cosmic rays : ~ 10-4 relative to the sea level • Expected at ~400 m underground • The rock composition : 238U ~ 4.8 ppm, 232Th ~ 6 ppm • 40K ~ 4 ppm (ICP-Mass) • Gamma background • With a shielding of 15cm Pb + 10cm Cu(OFHC) •  Can be controlled < 0.005 cpd (counts/keV/kg/day) • Neutron background • Photonuclear interaction of cosmic ray muon • Fission of 238U, (alpha,n) reaction • With 30cm polyethylene + 20 cm Liquid scintillator •  Can be controlled <0.001 cpd

  13. Gamma Background 100% HPGe installed in CPL W/o shielding 10cm Pb + 10 cm Cu (16 days data taking) 222Rn_up(226Ra)/222Rn_down(214PB,214Bi)=0.22+-0.06

  14. Neutron Background Measured with 0.5 liter BC501A liquid scintillator ~ 4x10-5 /cm2/sec Input to the GEANT4 simulation

  15. Internal background Radioisotopes in the crystal - most important background after the proper shielding 137Cs : t1/2= 30.07 year b decay to 137Ba* (Q = 1175.6 keV)  2 min life time, emitting 661.6 keV gamma Hard to reject => serious background at low energy 134Cs : t1/2 = 2.065 year b decsy to 134Ba* (Q=2058.7 keV)  immediate gamma emission Can be rejected easily => not a serious problem 87Rb : t1/2 half life = 4.75 x 1010 year (27.8% natural abundance) b Beta deacy to 87Sr (Q=282.3 keV)  no gamma emission Hard to reject => potentially a serious problem => reduction technique in material is known

  16. In acrystal currently available 60 cpd g-rays and b-rays of 87Rb, 134Cs, and 137Cs + GEANT Another crystal 137Cs : 13.3mBq/kg, 134Cs : 54.2mBq/kg,87Rb :~203ppb Internal background 0.63 cpd/1ppb 87Rb 0.3 cpd/1mBq 137Cs 0.005 cpd/1mBq 134Cs 137Cs : ~155mBq/kg, 134Cs : ~35mBq/kg, 87Rb : 3.9 ppb

  17. 238U, 232Th in the crystal 10~20 alphas/kg/day  ~3 ppt (U+Th)

  18. 134Cs(mBq/kg) 137Cs(mBq/kg) Measurement of Internal Background Crystal 137Cs, 134Cs : direct measurement (fit to the MC prediction) Rb : direct measurement + chemical analysis U, Th : direct measurement of alphas ~ 15 ppt Powder 137Cs, 134Cs : 100% HPGe detector Rb : chemical analysis (ICP Mass) CsOH, CsNO3, Pollucite, Water 137Cs, 134Cs : 100% HPGe detector

  19. Background measurement of powders Crystals CsOH CsNO3 CsMnO4 ~ 3mBq/kg CsI Powders 137Cs ~14mBq/kg Rb ~ 21 ppb

  20. 137Cs in Pollucite ? < 5.8 mBq/kg In CsI powder : 10~100 mBq/kg  In Pollucite : < 5.8 mBq/kg Processing water : 10.1  4.8 mBq/liter Extraction of CsMnO4 from Pollucite with pure water 2.05  3.16 mBq/kg

  21. 62 kg days exposure Surface effect ? CsI (30-50 keV) : 14.3 kg days NaI(Tl) (35-40 keV) : 330 kg days V.A. Kudryavtsev et al., hep-ex/0109013

  22. Shielding Design

  23. Detector Design CsI(Tl) 9cm x 9cm x 30cm ~ 11 kg Quartz PMT (3 inch RbCs) 5x5 = 25 crystals ~ 275 kg 20cm BC501A  tagging efficiency > 75%

  24. Sensitivity After 1 year data taking with 100 kg CsI(Tl) 2 keV threshold

  25. Summary & Prospect • Underground Lab. at CheongPyung is established • Environmental background : low enough • Comfortable place for long term experiment • Extensive R&D on CsI(Tl) crystal has been carried out • Low energy threshold ~ 2keV • Pulse shape discrimination of -rays : promising • Intrinsic background : almost understood • Shielding design/Simulation/Electronics/DAQ • Design almost at final stage • Prospect • ~100 kg CsI(Tl) crystal within this year • 1 year data taking will cover DAMA region

More Related