Supported by Grant-in-Aid for Scientific Research (C) 24540295 andGrant-in-Aid for Scientific Research on Innovative Areas 24104501

Development of liquid scintillator
containing zirconium complex forneutrinoless double beta decay
experiment
13th Vienna Conference on Instrumentation VCI2013
February 13th, 2013
Yoshiyuki FUKUDA (Miyagi University of Education)
Shigetaka MORIYAMA (ICRR, University of Tokyo)
Izumi OGAWA (University of Fukui),Neutrinoless double beta decay[T1/20n(0+ ->0+)]-1 =G0n(E0,Z)|M0n|2<mn>2
T1/2~a(Mt/DEB) a: abundance M: masst: meas.time DE: energy res. B: BG rate
Requirement : Low BG, Large target mass, High energy
resolution
Feb 13th, 2013

13th Vienna Conference on
Instrumentation2

For future experiments

high energyresolution
4%@2.5MeV

F.Piquemal@n2012

http://kds.kek.jp/getFile.py/access?contribId=37&sessionId=16&resId=2&materialId=slides&confId=9151~tons of target will be needed for next generation detector
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

3

Piquemal@n2012

Feb 13th, 2013

13th Vienna Conference on
Instrumentation4

Detector design for Zr in 100ton LS
Zirconium Complex in Organic liquid Scintillator(ZICOS)
Assuming 10w.t.% solubility
3m10m
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

5

Zirconium β-diketon complex
 Zirconium(IV) Advantage

acetylacetonate(Zr(acac)4)

 good solubility (over10w.t.%) in Anisole(PhOMe) Stable and cheep Commercial product Disadvantage
 Low scintillation light

Molecular weight : 487.66
Feb 13th, 2013yield

13th Vienna Conference on
Instrumentation

6

What’s problem : Absorption spectra ofZr(acac)4
 Emission peak ofanisole was observed
around 295nm.
 Absorption peak ofZr(acac)4 was observed
around 270nm.
Scintillation light fromPhOMe might beabsorbed by Zr(acac)4
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

7

Simple expectation for quenting Assuming to same cross section

for light
Light yield = L0 ×s1Nppo
s1Nppo + s2NZr
L0 : Light yield of anisole +PPO+POPOP
Nppo and NZr : No. ofmolecular for PPO and Zr(acac)4
s1,s2 : absorbance of PPO and Zr(acac)4
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

8Scontillation Light yield (60Co) withrespect to concentration of Zr(acac)4

Feb 13th, 2013

concentrationof Zr(acac)4ObservedchannelExpectedchannel

0 mg

3850

3850

50mg
(1.03X10-4)

3175

3138

100mg
(2.05X10-4)

2800

2651

200mg
(4.10X10-4)

2000

2018

300mg
(6.15X10-4)

1600

1613

500mg
(1.03X10-3)

900

1178

13th Vienna Conference on
Instrumentation

PPO 100mg : 4.52X10-4 mol
9Improve scintillation light yield Move absorption peak

to shorter wavelength How to do it?

substituent groups
http://www.hi-ho.ne.jp/hosomi/sotsuronCourtesy of Prof. Yoshiyuki Kowada(Hyogo University of Education)
Feb 13th, 2013

13th Vienna Conference on
Instrumentation10

Absorbance peak for several
substituent groups

Measured absorbancepeaks for several
substituent groups

Feb 13th, 2013



Expected absorbancepeak for several
substituent groups

13th Vienna Conference on
Instrumentation11

Zr b-diketon complex introducing
substituent groups (β-keto ester complex)
Zr(CH3COCHCOOCH(CH3))4 = Zr(iprac)4
mw : 711.92

Feb 13th, 2013

Zr(CH3CCOCHCOO
CH3)4 = Zr(etac)4
mw : 665.8113th Vienna Conference on
Instrumentation12Zr β-keto ester complex
Zr(iprac)4+(iprac)1.5
state: powder

Zr(etac)4
state : dry solid

Synthesized by Prof. Takahiro Gunji (Tokyo University of Science)

Solubility > 10 w.t.% for anisole
Feb 13th, 2013

13th Vienna Conference on
Instrumentation13

Absorbance spectra (Solvent effect)
Solution : Hexane

Solution : acetonitrile

solvent effectAbsorption peak moved to shorter wavelength
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

14

Absorbance in another solvent
Solution : Diethyl Ether

Solvent effect could
depend on the polarity(dielectric const.)
 Acetonitrile : 37.5

 Hexane : 1.89
 Anisole : 4.3



Need solution which hassame polarity as anisole Diethyl ether : 4.33

Still absorption peakremains around 270nm
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

15

Light yield of scintillation
Zr(iprac)5.5 in anisoleZr(etac)4 in anisoleSame quenting as Zr(acac)4 was observed
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

16

Requirement of scintillator solvent

Low polarity (dielectricconst.)
 No absorption ~270nm

Aromatic compounds
 luminescence >270nm

Safety for human bodyand environment Usual solvent for L.S.
Toluene / Xylene
Feb 4th, 2013

Aspen Winter Workshop--New
Directions in Neutrino Physics

17

Zirconium complex with luminescence Zr-ODZ complex

 Photo luminescencem.w. = 1040.18
Solvent : Acetonitrile
Concentration : 3.0×10-5 mol/L
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

18

Emission and absorption of Zr(ODZ)4• Emission wavelength :430nm
PMT sensitive• Absorption wavelength:
270nm and 320nm
different from excitation W.L.

• Solvent : PhCN(Benzonitrile)• Solubility : ~5w.t.%
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

19

Response for g-irradiation
Most of emission light fromPhCN was not used for theemission of Zr(ODZ)4.
 Secondary excitation of~340nm was used for theemission of Zr(ODZ)4.
 Estimated Quantum yield
was obtained ~30% at firstexcitation of ~240nm.
Need another solvent
which has shorter emission
wavelength than PhCN.
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

20

Summary High solubility of Zr β-keto ester in Anisole(>~10w.t.%) for ZICOS detector was achieved.
 Confirmed absorption peak moves to shorter
wavelength (275nm → 245nm) by introducing
substituent groups.
 Observed scintillation light yield decreased inproportion to the concentration of Zr β-keto ester due
to remaining absorption @ 280nm.
Need lowpolarity solvent.
 Quantum yield of Zr(ODZ)4 was achieved ~30%, but
it was not used for scintillator due to no overlap
between emission of solvent and absorption of ODZ.
Feb 13th, 2013

13th Vienna Conference on
Instrumentation21

BACKUPFeb 13th, 2013

13th Vienna Conference on
Instrumentation

22

Neutrinoless double beta decay using
liquid scintillator
Experimental limits forneutrino mass

 Requirement for<mn>:50~100meV high energy
resolution
4%@2.5MeV low background rate
0.01count kg-1 y-1
 ton scale of target

Liq. Scintillator is easy to scale up target volume
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

23

What’s problem
 Absorption spectra ofIn(acac)3 (indiumacetyl acetone) wasoverlapped with theemission spectra from
Anisole （Chem. Phys.
Lett., 435(2007), 252)
Same overlap of the emission and theabsorption spectrum would be occurred
even if different metal (Zr) was used.
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

24

Scintillation light yield (137Cs) withrespect to concentration of Zr(acac)4

Feb 13th, 2013

concentrationof Zr(acac)4ObservedchannelExpectedchannel

0 mg

2450

2450

50mg

1800

1997

100mg

1400

1687

200mg

950

1284

300mg

650

1038

500mg

300

750

13th Vienna Conference on
Instrumentation

25

Photo Luminescence and absorption of PPO
Photo luminescence Fluorescence device: HORIBA

FluoroMax-4
 Absorbance device : HITACHI
U-3000 Solvent : Benzonitrile (PhCN) Concentration : 1.0×10-5 mol/L 2,5-Diphenyloxazole
 Molecular mass : 221.26
 Max. emission wavelength :368.0nm Max. absorption wavelength :309.7nmFeb 13th, 2013

13th Vienna Conference on
Instrumentation

26

Photo Luminescence and absorption ofPOPOP

Photo luminescence Fluorescence device: HORIBA

FluoroMax-4
 Absorbance device : HITACHI
U-3000 Solvent : Benzonitrile (PhCN) Concentration : 1.0×10-5 mol/L 1,4-Bis(5-phenyloxazol-2-yl)benzene
 Molecular mass : 364.40
 Max. emission wavelength :423.6nm
 Max. absorption wavelength :364.1nm
13th Vienna Conference onFeb 13th, 2013

Instrumentation

27

Photo Luminescence and absorption of bisMSBPhoto luminescence Fluorescence device: HORIBA

FluoroMax-4
 Absorbance device : HITACHI
U-3000 Solvent : Benzonitrile (PhCN) Concentration : 1.0×10-5 mol/L 1,4-Bis(2-methylstyryl)benzene
 Molecular mass : 310.44
 Max. emission wavelength :426.6nm
 Max. absorption wavelength :355.3nmFeb 13th, 2013

13th Vienna Conference on
Instrumentation

28

Response for g-ray for tetrakis 8quinolinolate Zr complex loaded scintillator
Tetrakis (8-quinolinolate)
Zirconium complex (ZrQ4)

ZrQ4 50mg in PhCN-POPOP
Quantum
Yield=1.1%
obtained by
optical method

NMn+O-n

M = In, n = 3; M = Zr, n = 4

Light Yield toBC505:=7.3%

ZrQ4 m.w. = 689.07
Feb 13th, 2013

13th Vienna Conference on
Instrumentation

29