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 , 임대성

경북대 : 김홍주

이화여대 : 박일흥 , 이은경 , 한인식

칭화대 :J.J.Zhu

Double beta decay process

(A,Z) -> (A,Z+2) + 22

(A,Z)

(A,Z+1)

(A,Z+2)

Why decay is important?

0-DBD Present best experimental limits

1.8

<m>* (eV)

6.0> 1.8 102248CaOgawa I. et al., submitted 2002

Belli et al. submitted PLB

Experiment

< 1.4 4.1> 7 1023136Xe

Range <m>T1/20(y)Isotope

1.01.94.8

0.380.35

Bernatowicz et al. 1993

Zdenko et al. 2002

Ejiri et al. 2001

Aalseth et al 2002

Klapdor-Kleingrothaus et al. 2001

1.5Mi DBD 2002 < 0.9 2.1> 2.1 1023130Te< 1.0 4.4> 7.7 1024128Te< 1.8 6.2> 1.3 1023116Cd< 1.4 - 256> 5.5 1022100Mo< 0.3 - 2.5> 1.57 1025

< 0.3 - 2.5> 1.9 102576Ge

* 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 ; Nd2-ethylhexanoate, Zr2-ethylhexanoate.

LSC test sample HV + LSC

Setup VME

Zr2EH + LSC (50% ->Zr 3%) Nd2EH + LSC (50%->Nd 6.25%)

TetraButhyl Tin + LSC (50%->Sn 20%) TetraMethyl Tin + LSC (50%->Sn 40%)

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-

Source Detector(calorimetric technique)

+ high energy resolution- no event topology

Simulated spectra of 2 decay

experiment with 100Mo (Q=3034keV)

Modern Physics,Volume74, 2002

Calibration by Fermi-Dirac distribution

TBSN20% with Co60 source

Compton edge 1.12MeV

ADC

3.46keV/ADC channel

3″ PMT LED Test

ADC

S.P.E (100 times home-made preamp)

4.87 ADC channel/p e∙

→ 1.61p e/keV∙

TBSN 20% Energy spectrum

0 DB(Sn-124 Q=2287KeV)

keVkeV

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 = 1.2x1018 year by 90% C.L (Preliminary)

Summary

1. 1 day -> 1 year data taking

; 102 times increasing

2. TBSN 20% -> 50% loading

; 3 times increasing

3. World limit = 2~5x1017 year by 1952

Plan

• TBSN 50% and TMSN 50% study • Nd2EH and Zr2EH study• Background reduction• 2 DB study• Background understanding• More exact Calibration• electronics 500MHz FADC to identify and reject U238, Th 232 decay chains