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. Elastic Scattering of WIMP off a nucleus in the crystal
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 : 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) ~ GeV
Speed ~ 270 km/s
Density ~ 0.3 GeV/cm3
Cross section is very small : less than cm2
Recoil energy of nucleus is also very small :
less than100 keV
Background(gamma-rays, neutrons, X-rays,
cosmic rays) is very 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 expected limit curve
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. KIMS 지하 실험실 Homyung Mt.(虎鳴山) Reservoir Access tunnel(1.4km) 350m
Power plant
Homyung Mt.(虎鳴山)
Reservoir
Laboratory
Access tunnel(1.4km)
350m
Pukhan River(北漢江)

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
Conversion to CsOH solution
Waste 2
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. Spectrum 분석 I
- Background spectrum
테프론 삽입

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

13. Spectrum 분석 III LLD = 1.9 x 10-4 /s ( T = 350,000 s )
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 of pollucite
Spectrum 분석 IV
- Spectrum of pollucite
LLD = 2.8 x 10-4 /s
( T = 930,000 s)

15. Absolute detection efficiency - MC simulation I
EGS GEANT 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 D D D
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. Absolute detection efficiency - MC simulation II
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)

17. Absolute detection efficiency - MC simulation III
(662keV gamma) M evt M (X-G4l)/G4l
G4-low : Ege> : % % %
Ge full peak : % % %
G4-high : Ege> : % % %
Ge full peak : % % %
G : Ege> : % x %
Ge full peak : % x %
EGS4 : Ege> : x % %
Ge full peak : x % %
EGS4 : Ege> : % x %
Ge full peak : % x %
Systematic error caused by different model %

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
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 Bq/kg(0.027 pCi/kg) 이하로
줄이기 위해서 노력하고 있슴.