Development of Liquid Scintillator containing Zirconium Complex
for Neutrinoless Double Beta Decay Experiment
The 14th International Workshop on Next generation Nucleon Decay and Neutrino Detectors (NNN13)

Kashiwa, IPMU 11 – 13 November, 2013
Y.Fukudaa T.Muramatsua S.Moriyamab, Narengerilea , A.Obataa, I.Ogawac, A.Gunji*da Miyagi University of Educationb Kamioka Observatory ICRR, University of Tokyo

1. Neutrinoless Double Beta Decayc University of Fukui dTokyo University of Science (special thanks)

4. Scintillation yield with b-keto ester◆ Liquid scintillator containing Zr b-keto-ester complex◆ Neutrinoless double beta decay● Absorbance● Scintillation light yield● Lifetime and neutrino mass

[T1/20n(0+ ->0+)]-1 =G0n(E0,Z)|M0n|2<mn>2● Energy spectrum and lifetime measurement・monochromatic energy = Q-value
・T1/2~a(Mt/DEB) a: abundance M: masst: meas.time DE: energy res. B: BG rate

~70%

Requirement : Low background rate, Large target mass andHigh energy resolution◆ Double beta decay candidates● above 208Tl g line (2.614MeV) : 48Ca,150Nd, 96Zr, 100Mo,82Se…
● large abundance : 100Mo,82Se, 150Nd,96Zr● solved in liquid scintillator formed as
metal complex
Zirconium (96Zr) is possible candidate~36%

Confirmed absorption peak moves
275nm → 245nm in Hexane, but in
Acetonitrile

Observed scintillation light yielddecreased (but improved). Still exist
absorption peak around 270nm inAnisole ?.

◆ Liquid scintillator containing b-keto ester ligand● Scintillation light yield● Absorbance◆ Experimental limits for neutrinomass● high energy resolution :4%@2.5MeV = 100keV● low background rate :0.01count kg-1 y-1● large target mass :~ ton scale~84%

Goal: <mn>~10meV~60%◆ Detector design for Zr loaded liquid scintillator

Assuming 10w.t.% solubility
Same as EGAD

● high energy resolution :4%@2.5MeV = 100keV● low background rate :0.01count kg-1 y-1● large target mass :~ ton scale

3m

10m

Absorption peaks of b-keto ester ligands were found around at 240nm(not 270nm) even though the aromatic solvent. Scintillation light yieldrecovers almost double @ 5w.t.%.

5. Zirconium (diethyl malonato) complex◆ Tetrakis (diethyl malonato) Zr◆ Absorbance of ligand

Zirconium Complex in Organic liquid Scintillator (ZICOS)

2. Zirconium complex◆ Zirconium (IV) acetylacetonate◆ Quenting● good solubility(over 10w.t.% in Anisole)● stable and cheep

Zr(CH3CH2OCOCHCOOCH2CH3)4= Zr(demｌ)4● Expected lightLight yield = L0 ×s1Nppo
s1Nppo + s2NZr

M.W. : 727.84

short absorption peak (~210nm)
Scintillation light yield did
not decreased by theabsorption at all in any
concentration.

(commercial product)
Molecular weight (M.W.) : 487.66◆ Scintillation yield with respect toconcentration of Zr(acac)4

L0 : Light yield of anisole
Nppo : No. of PPO molecular
NZr : No. of Zr(acac)4 moleculars1: absorbance of PPO
s2 : absorbance of Zr(acac)4
concentration ofZr(acac)4Observed
Expected
ADC channel ADC channel

0 mg

3850

3850

50mg

3175

3138

100mg

2800

2651

200mg (1 w.t.%)2000

2018 (52%)

300mg

1600

1613

500mg

900

1178

1000mg (5 w.t.%)

Perfect!

6. Zirconium complex with luminescence◆ Zirconium ODZ complex
Molecular
weight :1040.18695 (18%)◆tetrakis (isopropyl acetoacetate) Zr ◆ tetrakis (ethyl acetoacetate) Zr● good solubility(5w.t.% in Benzonitrile
2w.t.% in Anisole)Zr(CH3COCHCOOCH(CH3))4= Zr(iprac)4Zr(CH3CCOCHCOOCH3)4= Zr(etac)4

M.W. : 711.92

M.W. : 665.81

tetrakis (diethyl malonato)
zirconium would be an
ultimate complex for
resolving the zirconium ina liquid scintillator.

◆ Luminescence● Emission: 430nm● Absorption : 270nm
and 320nm● Quantum yield :~ 30%.
Scintillation Llght from PPO could be
used for the emission of Zr(ODZ)4.

This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (No.24104501)
from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and a Grant-in-Aid for
Scientific Research (C) (No.24540295) from the Japanese Society for the Promotion of Science (JSPS).