Study of Liquid Scintillator Properties at RENO

김수봉 , 김현수 , 박강순 , 박정식 , 신경하 , 이재승 , 최선호 , 황원석 ( 서울대학교 )공대정 , 김동희 , 김우영 , 사무엘 스테파냔 , 서준석 , 아딜 칸 , 안드레이 김 (경북대학교 ) 박인곤 ( 경상대학교 )박명렬 ( 동신대학교 )안정근 , 이효상 ( 부산대학교 )권은향 , 김동현 , 박차원 , 백승록 , 유인태 , 최수용 , 최영일 ( 성균관대학교 ) 강운구 , 김영덕 , 마경주 , 전은주 ( 세종대학교 )김성현 , 김재률 , 주경광 , 임인택 , 장지승 , 정인석 ( 전남대학교 ) 오영도 ( 포항가속기연구소 )N. Danilov, Yu, Krylov, G. Novikova, E. Yanovich (INR/IPCE)

KPS at DCCApr. 17~18, 2008

Reactor Experiment for Neutrino Oscillation

Inverse Beta Decay

E4Lm

sin)2(sincosE4

Lmsin)2(sin1)(P

2212

122

134

2312

132

ee

Su

rviv

al Pro

bab

ility

13 Dominant

12 Dominant

“near” “far”

e

eeE<10 MeV

p

νe

e+

n

Gd

γ

γ γ

γ

~30μs

Delayed signalE ~ 8MeV

γ

γ

prompt signal

enpe

Neutron captured at Gd

Reactor

RENO Detector Buffer region with PMT

Front view

Side view

RENO detector consists of four concentric cylindrical

parts.

Target & Gamma Catcher will filled Liquid Scintillator.

Liquid Scintillator at a Glimpse

Transparency High light yield Long term stability High radiopurity Safety matter Reasonable price Massive quantity

available

Base solvent For mixing FluorWave-length

shifter

PC, PXE MO, Dodecane PPO, BPO bis-MSB, POPOP

Base solvent + primary scintillating fluor + secondary wavelength shifter

Required Properties

General Elements of Liquid ScintillatorEffect of wavelength shifter

Before

After

PMT sensitive region

PC is widely used for base solventfor its excellent transparency and fluor dissolution.

RENO Base Liquid Scintillator

PC(20%) + dodecane(80%) + PPO(3g/L) + bis-MSB(30mg/L)

• Gd-LS R&D with the Russian INR/IPCE group : Gd-LS stability: good for > 6 months• Performance study of various LS recipes : : light yield : transmission & attenuation lengths• Development of purification system : Al2O3 adsorption : Vacuum distillation : Water extraction, etc• Long-term stability test• Reactivity test with acrylic • Study of Linear alkyl benzene(LAB)

Purification with Al2O3

Before

After

Purified ingredients is important!

LAB

CnH2n+1-C6H5 (n=9~14)

PC LAB

Molecular formula C9H12 CnH2n+1-C6H5

Molecular weight(g/mol)

120.19 233~237

Flash point (°C) 48 130

Density(g/ml) 0.89 0.86

Compatibility(acryllic)

Negative, need diluent

Test in progress

Cost Moderate Cheap

Fluor dissolution Very good Moderate

Domestic availability Abroad Available

etc Harmful odor Colorless & odorless

LAB

n Percent(%)

9 0.47

10 9.7

11 33.85

12 34.72

13 20.83

14 0.43

GC-MS result of LAB

Light Yield Measurement

Optimization of PPO, bis-MSB Concentration

Light Yield Measurement

LY saturated when PPO 3g/L and bis-MSB 30mg/L

Gadolonium

Gd has the highest thermal neutron capture cross-section, 49000barn.

Gd Isotop

e

Abundance(%)

Cross-section(barns)

152 0.20 735

154 2.18 85

155 14.80 60900

156 20.47 1.50

157 15.65 254000

158 24.84 2.20

160 21.86 0.77

0.1% loading is enough for RENO

Gd need to transform to Gd-CBX for loading in organic phase

CEDTA * VEDTA = CGd * VGd

Where C = Concentration V = Volume

Needed components• Xylenol-orange : Indicator• Buffer solution• EDTA

Gd concentration check : EDTA Titration

Target region fill with Gd loaded Liquid Scintillator.

Light yield Measurement with Cs source

Cs source emits 0.668 MeV gamma

Monte Carlo Simulation for 20mL LS

NaI Crystal with 3cm*3cm*3cm

20mL LS with LAB + optimized PPO & bis-MSB

Measurement was performed in special dark box with 2 inch PMT.

LS Radiopurity Measurement

• Natural Radioactive material give rise to background.

• Internal background material : 238U, 232Th, 40K

• Dominate from PMT glass : 10Hz

• LS radioimpurity contribute to background : 10-12g/g ~7Hz

• Accurate radioimpurity quantity measurement with ICP-MS.

Sample Th U

ICP-MS 0.011±2.94%

0.008±7.8%

10 times enrichment

0.0011 0.0008

Unit : ppb=ug/L

ICP-MS result of LAB

MC simulation of internal background

Summary

• LAB has comparable properties with PC.

• Optimized PPO and bis-MSB concentration for LAB.

• Gd concentration can be checked with EDTA titration.

• Light Yield was measured in special dark box with compton edge FWHM.

• LS radioimpurity quantity was measured accurately with ICP-MS.

• Long term stability test is on going.