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* Staudt, Muto, Klapdor-Kleingrothaus Europh. Lett 13 (1990) 31
Why metal loaded liquid scintillator?
• Advantage a) high-Z can be loaded to LS (>50% or more) b) Fast timing response (few ns) c) Low cost of LS, Large volume is possible d) U/Th/K background for LS is low and purification is known
• Disadvantage a) Bigger volume is necessary (C,H in LS, low
density) b) Lower light output (~15% of NaI(Tl))
Passive shielding at Y2L(700m depth)
Pb shield (15cm)
PE shield (5cm)
Mineral Oil shield (30cm)
Double beta decay detector
Dimension
R = 5cm
H = 14.94cm
V = 1.15L
Plastic
Quartz glass
Teflon
TMSN40%
• TMSN : 347ml (456g, 1.314g/ml)
• PC : 753ml (671g, 0.891g/ml)
• TMSN40% = TMSN + PC
• TMSN : 456g/(456g + 671g) = 40%
• Sn = 456g/(456g + 671g) * 119/178 -> 27%
TMSN40% Calibration
keV keV
-> Resolution 8% , 0.9keV/ADC Channel
• Resolution = 1 / sqrt(N)
Resolution 8% -> 156.25 pe
• 54Mn 834keV
156.25pe/834keV = 0.187pe/keV
TMSN40% Energy Spectrum
by 500MHz FADC
pol3 + gaus fitting
keV
Sensitivity
• T1/2 = log 2 e N T / dS
• e : efficiency
• N : Number of double beta nuclei
• T : Data taken time with year
• dS : mean value + 1.64 of Gaussian fitted area
(mean value is Q-value)
• T1/2 = 1.71x1019 year by 90% C.L (Preliminary)
Intrinsic radio-impurities
– coincidence candidates
1. 238U chain
214Bi : 3.27 MeV -decay214Po : 7.834 MeV -decay
– Lifetime of 214Po = 164.3 us– 190 keV Energy threshold
214Po – sidesubtraction
main
side
214Bi - spectrum
214Po – spectrum
214Po - decay
- Quanching factor = 804/7834 = 10.3%
- 4842 개 /75day = 65 개 /day
Q=3.27MeV
Q=7.834MeV
keV
214Po - half-life
s
T 1/2 = 235.9us * log(2) = 163.5 us
T 1/2 = 163.7us
s
2. 232Th chain
212Bi : 2.254 MeV -decay 212Po : 8.784 MeV -decay
– Lifetime of 212Po = 299 ns– 1ch = 2ns
1x
3x
channel
212Bi - spectrum
212Po - spectrum
212Po - decay
- Quanching factor = 940/8784 = 10.7%
- 281 개 /75day = 3.8 개 /day
Q=8.784MeV
Q=2.254MeV
212Po - half-life
T 1/2 = 422.9ns * log(2) = 293.1 ns
T 1/2 = 299ns
ns
Summary
1. TMSN40% by 500MHz FADC (75 days)
T1/2 = 1.71x1019 year by 90% C.L
2. 214Po - decay -> 65 개 /day
3. 212Po - decay -> 3.8 개 /day
4. World limit = 2~5x1017 year by 1952
Plan
• G4 simulation – intrinsic radio-impurities -> 238U, 232Th decay chains • Background reduction• Nd2EH and Zr2 EH study