Development of metal-loaded liquid scintillators for the double beta decay experiment 연세대 : 황명진, 권영준 서울대 : 곽정원, 김상열, 김선기, 김승천, 김태연, 명성숙, 방형찬, 이명재, 이직, 이현수 세종대 : 김영덕, 이정일 경북대 : 김홍주 이화여대 : 박일흥, 한인식 IHEP:J.Li 칭화대 :J.J.Zhu,D.He

Double beta decay process (A,Z) -> (A,Z+2) + 2  2 (A,Z) (A,Z+1) (A,Z+2)

Why  decay is important?

0 -DBD Present best experimental limits 1.8 * (eV) 6.0 > 1.8  Ca Ogawa I. et al., submitted 2002 Belli et al. submitted PLB Experiment < > 7  Xe Range T 1/2 0  (y)Isotope Bernatowicz et al Zdenko et al Ejiri et al Aalseth et al 2002 Klapdor-Kleingrothaus et al Mi DBD 2002 < > 2.1  Te < > 7.7  Te < > 1.3  Cd < > 5.5  Mo < > 1.57  < > 1.9  Ge * 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))

Tin loading study Tin compound 1) Tetramethyl-tin (40%w50%) : flammable,expensive 2) Tetrabutyl-tin (19%w50%) LS : Solvent+Solute * Solvent ; PC 1L * Solute ; POP 4g * Second-solute ; POPOP 15mg * Others ; Nd 2 -ethylhexanoate, Zr 2 -ethylhexanoate.

LSC test sample HV + LSC SetupVME

Passive shielding at Y2L(700m depth) Pb shield (15cm) PE shield (5cm) Mineral Oil shield (30cm)

Double beta decay detector Dimension R = 5cm H = 15.2cm V = 1.18L Plastic Quartz glass Teflon

e-e- e-e- Source  Detector (calorimetric technique) h + high energy resolution - no event topology Simulated spectra of 2  decay experiment with 100 Mo (Q=3034keV) Modern Physics,Volume74, 2002

 –  coincidence candidates 238 U chain 214 Bi : 3.27 MeV  -decay  214 Po : MeV  -decay – Lifetime of 214 Po = ms – 100 keV Energy threshold

214 Bi  -decay  214 Po - decay s -> T 1/2 = 0.166ms

214 Bi  -spectrum 214 Po  -  spectrum Q=7.833MeV 214 Po -  decay - Quanching factor = 9.1% - 67 개 /day Ee(keV) Q=3.27MeV Ee(keV)

TMSN50% Energy Spectrum by CAMAC pol3 + gaus fitting Ee(keV)

TMSN50% Energy Spectrum by 500MHz FADC pol3 + gaus fitting Ee(keV)

Sensitivity T 1/2 = log 2  e  N  T / dS e : efficiency N : Number of double beta nuclei T : Data taken time with year dS : mean value  of Gaussian fitted area (mean value is Q-value)

Summary 1. TMSN50% by CAMAC -> 123 days T 1/2 = 5.56x10 19 year by 90% C.L 2. TMSN50% by 500MHz FADC -> 33 days T 1/2 = 3.41x10 19 year by 90% C.L 3. World limit = 2~5x10 17 year by 1952

Plan Nd 2 EH and Zr 2 EH study Background reduction 2 DB study Background understanding More exact Calibration U238, Th 232 decay chains study