Development of InP solid state detector and liquid scintillator
containing indium complexes for a measurement of pp/7Be solar neutrinos
Y.Fukudaa T.Benia T.Izawad K.Kasaia S.Moriyamab T.Nambac A.Obataa H.Sekiyab K.Watanabeaa Miyagi University of Educationb ICRR, University of Tokyo

c ICEPP, University of Tokyo d Solid state division, Hamamatsu Photonics K.K.

1. Introduction◆ Purpose : Measurement of precise mixing angle θ12・ 96%C.L. allowed region obtained by global fit
LMA solution (blue) : Cl + Ga + SK (D/N spectrum)
KamLAND (green) → confirm ∆m12227°< θ 12<37°・ mixing angle θ12 is not fixed compared with θ23 (obtained by Atm. ν)・ survival probability would increase at 5MeV or less in case of LMAsolution, and the shape depends on the value of θ12.
pp/7Be solar neutrino spectrum could obtain precise θ 12
● on-going solar 7Be experiment・ KamLAND (Liquid scintillator, electron elastic scattering [ES])・ Borexino (Liquid scintillator, ES)● future solar pp/7Be experiment
・ XMASS (LXe, ES, DARK MATTER)
・ LENS (Liquid scintillator loaded In/Ye, charged current [CC])・ others
Y.Suzuki@Neutrino2004

4. IPNOS phase-I experiment◆ Detector
・ 30cm cubic chamber (like XMASS 100kg prototype detector)
・ InP multi-pixel detector inside of Liquid Xenon
・ Chamber includes ~10kg InP detector◆ Purpose・ demonstrate LowBG environment
・ long stable operation (1 ppν event will be expected for half year)◆ Requirements to detect γ3・ transparency of Au/Cr electrode : 0.43 X 0.39 = 0.17
・ assuming same conversion efficiency : 0.3
・ assuming surface coverage : 0.8

Expected scinti. light yield ~ 3keV

not enough…

・ modify shape of electrode such as mesh structure
・ assuming 50% for naked area then transparency recovers 0.58

Expected scinti. light yield ~10keV

maybe ok!

◆ Contribution to determination of θ13

5. Liquid scintillator containing
metal complexes

・ Precise θ12 from solar neutrino experiment and KamLAND
experiment will contribute to determination of θ13(Phys.Rev.Lett. 110(2008)141801)◆ Technique of low energy solar neutrino detection● Advantage
・ large cross section (~640SNU)
・ direct counting for solar neutrinos
・ sensitive to low energy region (Eν ≧ 125keV)・ energy measurement (Ee = Eν － 125keV)・ triple fold coincidence to extract neutrino signal
from huge BG (e1 +γ2 + γ3 )● Disadvantage
・ natural β-decay of 115In
115In + ν → 115Sn* + e (τ1/2 = 4.4 × 1014 yr , Ee≧498keV)e
1
115Sn*(4.76µs) → 115Sn + γ (115keV) + γ (497keV)・ possible BG due to correlated accidental
23coincidence by radiative Bremsstrahlung

R.S.Raghavan Phs.Rev.Lett.37(1976)259◆ Development of liquid scintillator using Indium complexes● goal : solublity : 5 wt%, light yield : 60% of BC505, attenuation length : 2~3m
● tris(8-quinolinolate) indium complex (InQ3)・ AlQ3 has been established as organic Electro Luminescencematerial (maximum luminescence @ 530nm)
・ InQ3 should have same property of luminescence● Synthesis of InQ3 complex● Solution of InQ3 in organic solvent◆Indium Project on Neutrino Observation for Solar interior (IPNOS) experiment●Hybrid structure of InP and external scintillator3.0cm

28.5cm
1.0cm

・InP multi-pixel detector (10mmX10mmX0.2mm cell)・external scintillator to detect γ1 and γ2●4tons of 115In detector for solar ν experiment
・ InP : 5.1tons (2.0X106 modules with ∆E/E~10% )・ high Z material for external scintillator
・ total size ~5m X ~5m X ~5m (depends on structure)◆ Luminescence of InQ3 complex

Solvent : Benzonitrile (PhCN: C6H5CN)
density : 1.0g/mL flash point : 75℃
Photon emission : 291nm@maximum
Solubility of InQ3 complex: 2wt%Attenuation length : 66cm (@0.5wt%)● Light (energy) transfer to InQ3・ PPO dissolved as a wavelength
shifter (0.15wt%)

・ Number of expected events assuming no ν oscillation → 1885
・ Number of expected event assuming LMA solution with Ee≧100keV → 720

θ12 = 30°- 34°

Statistical and theoretical error in total → ~3.5 %2. SI InP cell detector
Schematic view of InP detector◆InP detector in vacuum dewar

Size:
10mm×10mm×0.2mm
Electrode :・ Ohmic contact
・ Au vacuum evaporation
・Insulator (SiN) to avoid
leak current◆Response for γ−ray from radioactive source

Setup Clearpulse 5102 preamplifier
Clearpulse 4417 shaping amplifier
CAEN V419 peak sensing VME ADC

・ Measured clear photo- peak , but twopeak structure
・ Lower peak: induced charge(Led~200µm Lhe ~ 30µm)
Higher peak: e- full collection
・ Energy of electron-hole pair
production :3.5eV・ Energy resolution : 25%@122keV

3. InP photon detector

Courtesy of Prof. T.Muramatsu(Miyagi University of Education)● Measurement of photo luminescence・ Device : HORIBA FluoroMax-4 (2-dim scanning)・ Solvent : PhCN Concentration : 0.1wt%
・ Maximum excitation wavelength : 460nm
・ Maximum emission wavelength : 560nm◆ Performance of liquid scintillator● Setup・ Hamamatsu H6410 2inch photomultiplier・ Fisherbrand 20mL Borosilicate Glass Scintilation Vials
・ Acrylic light guide・ LeCroy 1182 charge sensitive VME ADC
・ coincidence method was used for eliminating BG● Response for γ−ray from radioactive source ● Light yield and quantum yield
・ γ-ray spectrum was observed
・ No significant difference
for concentration of InQ3・ all scintillation lights haveλ > 520 nm

Photo luminescence causedby γ-ray was confirmed◆ InP detector inside Liquid Xenon

・ quantum yield : 6% (3.9% ref. Inorg.Chem.46 (2007)5700)
・ relative light yield to BC505 : 2% (36% for PhCN+PPO)

6. Next step・ Liquid Xenon has large cross section to detect γ-ray
・ InP detector should keep cool to reduce dark current◆ For IPNOS phase-I● Measurement of scintillation light from LXe

If InP detector would work as photon detector ,LXe should be good scintillator to detect γ2 and γ3◆ Development of InP photon detector
・ thin electrode to pass the lights(Au :100Å/ Cr : 100Å)
・ detector size 6mm×6mm×0.2mm

R8778 photomultiplier
Producted by Hamamatsu
Photonics (used for XMASS)◆ Measurement of CsI scintillation lights
・ CsI light source pulsed by 241Am α (3MBq : average 6α’s)・ solid angle : 0.2
・ transparency of Au/Cr electrode : 0.57 X 0.37 = 0.21
・ observed signal : 0.5 ~ 2.0 fC

External and internal conversion efficiency : 0.3

Success to detect both
scintillation lights and γ’s

・ direct measurement of LXe scintillation light・ construct small LXe chamber (volume : 0.15L)・ coincidence method using for R8778 PMT
・ finalize shape of electrode for InP detector
supported by Grant-in-Aid for Scientific
Research on Priority Areas 22011001◆ For Metal complex loaded liquidscintillator● In complex
・ modify 8-quinolinolate ligand to add
substituent groups (Cr, No2, …)・ use another ligand which should be OEL(emission wavelength ~400nm)
・ modify b-diketonate complex to shift
absorption wavelength (J. Radioanal. Nucl.
Chem., 258(2003)255)● Zr , Mo, Cd, Nd complex
・ Other metal Zr, Mo, Cd, Nd complex will
be good detector for 0νββ experiment・ goal :5wt% solubility and 2%@3MeV
energy resolution
supported by Grant-in-Aid for
Scientific Research (C) 22540303