Development of Liquid Scintillator containing Zirconium Complex
for Neutrinoless Double Beta Decay Experiment
XXXVI International Conference on Neutrino Physics and Astrophysics (Neutrino2014)
ndth
Boston, USA, 2 – 7 June, 2014

Y.Fukudaa , T.Muramatsua, S.Moriyamab, Narengerilea, A.Obataa, I.Ogawac, A.Gunji*d, M.Tsukada*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)

3. Scintillation yield with b-keto ester◆ Liquid scintillator containing Zr b-keto-ester complex● Scintillation light yield● Absorbance spectra in Anisole◆ Neutrinoless double beta decay● 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%

Requirements : 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%

Observed scintillation light yielddecreased (but improved). Still exist
absorption peak around 280nm inanisole ?

Small bump around 280nm was foundeven after ~ 1 week. Impurities might
be dissolved in Anisole, so we have topurify complex by using sublimation.

◆ Backscattering method for measurement of light yield and energy

resolution◆ Detector design for Zr loaded liquid scintillator

Assuming 10w.t.% solubility

3m

10m

Goal: <mn>~10meV● light yield : 60% for BC505● high energy resolution :4%@2.5MeV = 100keV● low background rate :0.01count kg-1 y-1● target volume : ~ton scale

Monochromatic energy
electrons were selectedby tagging backscattered gammas with
NaI scintillator.

NaI
sourceSingle peak could be usedeven though liquid
scintillator in small vial.

LS◆ Performance of liquid scintillator (assuming purified)

Zirconium Complex in Organic liquid Scintillator (ZICOS) experimentfor neutrinoless double beta decay● Light yield vs concentration● Resolution vs concentration

2. Zirconium b-keto ester complex◆tetrakis (isopropyl acetoacetate) Zr ◆ tetrakis (ethyl acetoacetate) Zr

Zr(CH3COCHCOOCH(CH3))4= Zr(iprac)4Zr(CH3COCHCOOH2CH3)4= Zr(etac)4

M.W. : 663.87

M.W. : 607.76

Solubility > 10w.t.% for anisole◆ Absorbance spectra for complex

and emission spectra for anisole◆ Absorbance spectra for complex

Light yield was ~40% to that of BC505 (almost same as our cocktail) , andenergy resolution was 4.1% @2.5MeV for 10 w.t.% concentration assuming
40% photo coverage. They almost achieved to our goal!.

after 1 week

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

Zr(CH3CH2OCOCHCOOCH2CH3)4= Zr(demｌ)4

M.W. : 727.86◆ Scintillation light yield● Absorption peaks of Zirconium
b-keto ester complex : 245nm● Small bump : ~280nm◆ Explanation of small bump● Small bump was disappeared
after ~ 1 week.
● Impurities contained in the complex
could be precipitated.

Small bump wasdisappeared for topregion, but still
remained forbottom region ofthe vial. These
could be explainedby the precipitation.

shorter wavelength (~210nm)
No quenching due to overlap between theabsorption of ligand and the emission ofanisole should be occurred even though highconcentration.

Perfect!
Absorption shapes arecompletely same between
complex and ligand.

Light yield will be almost same as that of BC505
and energy resolution will be ~2%@2.5MeV for
10w.t.% concentration.

This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (No.24104501
and No.26105502) and a Grant-in-Aid for Scientific Research (C) (No.24540295) from the JapaneseSociety for the Promotion of Science (JSPS).