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암흑물질 탐색을 위한 CsI 섬광검출기의 특성시험 - CsI 결정제작과정의 Cs 화합물의 방사능 측정 -

암흑물질 탐색을 위한 CsI 섬광검출기의 특성시험 - CsI 결정제작과정의 Cs 화합물의 방사능 측정 -. KIMS (Korean Invisible Mass Search) Collaboration 김태연 , 양명수 , 최진명 , 이현수 , 양혜영 , 원효식 , 박현서 , 원은일 , 박일흥 , 김선기 ( 서울대 ), 강운구 , 김영덕 ( 세종대 ), 권영준 , 김홍주 , 김상열 , 황명진 , 이종호 ( 연세대 ), 한인식 , 김지훈 ( 이화여대 ),

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암흑물질 탐색을 위한 CsI 섬광검출기의 특성시험 - CsI 결정제작과정의 Cs 화합물의 방사능 측정 -

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  1. 암흑물질 탐색을 위한 CsI 섬광검출기의 특성시험 - CsI 결정제작과정의 Cs 화합물의 방사능 측정 - KIMS (Korean Invisible Mass Search) Collaboration 김태연, 양명수, 최진명, 이현수, 양혜영, 원효식, 박현서, 원은일, 박일흥, 김선기(서울대), 강운구, 김영덕(세종대), 권영준, 김홍주, 김상열, 황명진, 이종호(연세대), 한인식, 김지훈(이화여대), 유인태, 조일성, 노승훈, 최동혁(성균관대), 최성렬(전북대), 고병원(과기대), 서은숙, 이무현(Univ. of Maryland) J.Li(Institute of High Energy Physics, Beijing), H.Wong(Acanemia Cinica, Taipei), M.Z.Wang(National Taiwan University, Taipei)

  2. 암흑물질탐색 실험 암흑물질에 대한 관측증거 1) 나선형 은하의 회전속도 2) Clusters of galaxies - Virial mass - Giant arcs

  3. 직접 검출 원리 되튄 원자핵의 (이온화) 에너지 손실을 검출 Elastic Scattering of WIMP off a nucleus in the crystal WIMP - Supersymetry particle - Lightest stable particle - Neutral particle - Mass : 10 -1000 GeV - Density : 0.3 GeV/cm3 - Speed : 230 km/s WIMP Cs I Recoiled nucleus Energy loss by ionization and lattice vibration

  4. 검출기 요구조건 WIMP Mass (the Lightest Supersymmetry Particle) ~ 10 - 1000 GeV Speed ~ 270 km/s Density ~ 0.3 GeV/cm3 Cross section isvery small: less than 10-41 cm2 Recoil energy of nucleus is alsovery small: less than100 keV Background(gamma-rays, neutrons, X-rays, cosmic rays) isvery large • Detector has large target mass and long-term stability • Detector can measure tiny energy ~ few keV • Detector have to be made of pure material • Detector have to be located underground

  5. KIMS’s detector KIMS’s expected limit curve ( 1 year run ) Total 134Cs 137Cs 87Rb = 1 ppb 134Cs = 30 pCi 137Cs = 0.3 pCi 87Rb

  6. Homyung Mt.(虎鳴山) Reservoir Access tunnel(1.4km) 350m Pukhan River(北漢江) Laboratory Power plant KIMS 지하 실험실

  7. Muon flux PSD 진행중인 테스트 MC PMT test Neutron beam test Crystal

  8. Background energy spectrum of CsI(Tl) crystal : Budker Institute of Nuclear Physics (Ukraine) : Shanghai Institute of Ceramics (China) : Crismatec (France)

  9. Production of CsI powder Pollucite Ore Digestion Quartz Purification of Cesium salt solution Waste 1 Waste 2 Conversion to CsOH solution Evaporation CsOH solution(50%) Carbonization Filtration Cs2CO3 Solution CsOH solution + HX CsHCO3 +HX Pure technical Cs Salts High Purity Cs Salts Cs Metal

  10. Cs 화합물의 방사능 측정 시료 : CsI powder(A,B,C,D) 검출기 : HPGe (GMX, 23 %) CsOH CsNO3 Process water(A) 18 Mohm water 원광(pollucite)

  11. 테프론 삽입 Spectrum 분석 I - Background spectrum

  12. 133Ba 30.6(X-ray) 30.9(X-ray) 53.1(X-rsy) 79.6 80.9 276.4 302.8 356.0 383.8 137Cs and 60Co 31.8(X-ray) 32.2(X-ray) 36.5(X-ray) 661.6 1173.2 1332.5 Spectrum 분석 II - Background 원천 Ratio of the peak area w/ teflon to w/o teflon (calibration sources) Ratio of the peak area w/ teflon to w/o teflon (background)

  13. Spectrum 분석 III L.A.Currie, Anal. Chem. 40, 586(1968) Lower Limit of Detection LLD = 1.9 x 10-4 /s ( T = 350,000 s )

  14. Spectrum 분석 IV - Spectrum of pollucite LLD = 2.8 x 10-4 /s ( T = 930,000 s)

  15. Absolute detection efficiency - MC simulation I ----------------------------------------------------------------- EGS4 GEANT3 GEANT4 ----------------------------------------------------------------- Coding Mortran( F77) Fortran C++ EM energy range Low to high High( low) Low, High Interaction EM only EM, HAD EM,HAD, n, decay Test Long term Long term Ongoing Geometry setup Terrible Easy Easy Interaction update Diffcult Difficult Easy Visualization 3D 2D 3D • Random event generation at Marinelli beaker where CsI powder is filled. • 661keV gamma( 667 keV), 1MeV electron with 1M , 100M events. • Check energy deposition in CsI or Ge. • G3 by Y.D.Kim, G4 by H.J.Kim and EGS4 by T.Y.Kim and J.H.Kim

  16. Deposited energy in Ge detector (gamma-ray of 662 keV) Deposited energy in CsI powder (gamma-ray of 662 keV) Deposited energy in Ge detector (beta-ray of 1 MeV) Absolute detection efficiency - MC simulation II

  17. Absolute detection efficiency - MC simulation III (662keV gamma) 1M evt 100M (X-G4l)/G4l -------------------------------------------------------------------------------- G4-low : Ege>0.0 : 6.69 % 6.688 % 0.0 % Ge full peak : 1.62 % 1.617 % 0.0 % G4-high : Ege>0.0 : 6.71 % 6.691 % 0.0 % Ge full peak : 1.59 % 1.596 % -1.3 % G3 : Ege>0.0 : 6.63 % x -0.9 % Ge full peak : 1.58 % x -2.2 % EGS4 : Ege>0.0 : x 6.581 % -1.6 % Ge full peak : x 1.644 % 1.7 % EGS4 : Ege>0.0 : 6.69 % x 0.0 % Ge full peak : 1.64 % x 1.4 % -------------------------------------------------------------------------------- Systematic error caused by different model +- 2%

  18. Absolute detection efficiency - MC simulation IV Calculated detection efficiency curve

  19. Radioactivity of the samples

  20. 결 론 - 현재 상용화 되어 있는 CsI 결정으로는 기존실험들의 검출기 sensitivity와 견줄 수 없슴 . - 적극적으로 CsI 결정 제작과정에 관여해야 할 것임. - 현재 상용화 되는 CsI 결정의 137Cs 내부 방사능은 0.025 - 0.1 Bq/kg 보다 큼 (결정생성 전단계의 CsI powder 측정결과). - 원광(pollucite ore)에서의 137Cs 내부 방사능 오염양은 현재의 측정장치로는 효과적으로 측정하기 힘듬. - 137Cs 내부 방사능을 0.001 Bq/kg(0.027 pCi/kg) 이하로 줄이기 위해서 노력하고 있슴.

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