Direction-Sensitive Dark Matter Search Using Tungstate Scintillator

Shunsuke KUROSAWA1,2

H. Sekiya3, M. Tsukahara2, M. Abe2, A. Yamaji1, R. Murakami1, T. Horiai1, S. Kodama1, Y. Shoji1, M. Yoshino1, Y. Ohashi1,

Y. Yokota1, K. Kamada1, A. Yoshikawa1 , A. Ohnishi21Tohoku Univ. (Japan), 2Yamagata Univ. (Japan), 3The Univ. of Tokyo Japan

The Vienna Conference on Instrumentation (VCI 2019)2019/02/20 @ Vienna

Contents Introduction

What’s anisotropic property Crystal growth and its

evaluation (ZnWO4) Evaluation for other crystals Summary

Our activities in Sendai/Yamagata Japan

Halide scintillator

Eutectic scintillator

Ceramics scintillator

Dark Matter search& double beta exp.

Oxide scintillator

Organic Crystal

(Kurosawa+)

(Kurosawa+)

(Kurosawa+)

Development of gamma-ray imaging devices

Poster B (TPC+ScintillatorCompton camera)

Othersi.e. Metals

Dark matter = WIMP (weakly interacting massive particles)

WIMP wind : direction information

Wind from Cygnus

If we detect the direction of the wind, sensitivity can be improved.

Dark matter = WIMP (weakly interacting massive particles)

WIMP wind : direction information

Wind from Cygnus

If we detect the direction of the wind, sensitivity can be improved.

E=500V/cm

10cm

10cm

10cm

0.2mmCu wires

10×10×10cm3 detection volume

Ar 90%+C2H6 10% 1atm

Electron tracks ～500keVGaseous detector

Kyoto Univ. Cosmic-ray Lab.

How to detect the direction

Gas detector has low detection efficiency

Normal Scintillation Material

Radiation

ScintillatorHomogeneous

Isotropic

Scintillation photons

Radiation

Scintillator

Dishomogeneity?

Light output depends on the incident directions ??

Radiation

Abnormal(?) Scintillation Material (anisotropic)

Scintillator Scintillator

Radiation

Solid state detectoranisotropic response

Directional response with MeV alpha particles

Only 7%

keVnr

ZnWO4 stilbene crystal

HS et al., Physics Letters B 571 (2003) 132 IDM 2004

Cappella et al., Eur. Phys. J. C. 73 (2013) 2276

~30 – 50 %

Crystal grwoth

purpose： investigation of anisotropic response with large size crystal

Czochralski process

Starting Material

ZnO, WO3 (99.99％ pure)

Rate 0.5mm/hseed ZWO (001)Atmosphere Ar+O2(2%)Rotation 12rpm

As-grown crystal

30ｍｍ

Crystal irradiated with UV photons

Approx.(001) Approx.

(100)

(010)

a [Å] b[Å] c[Å] α [deg] β [deg] γ [deg]4.69060 5.71820 4.92690 90.0000 90.6210 90.0000

Laue pattern for orientation cut

Transmittance for each orientation

No differencefor each

orientation

Emissionspectrum

Emission intensity (a. u.)

Aprpox. (001)

Approx. (100) (010)

spectrometer: V-530,

JASCO

Err. ±５％

Measurement of light output for each orientation

日本物理学会 年秋季大会 大阪市立大学2015 28aSJ-10

Photo multiplierHamamatsu R7600-200

RI Source

MCA8000A

sample

preampORTEC 113C=1000pF

shaperORTEC 752AShaping time:

10 µsecAm-241

9mm

Photoelectric surface Am-214 source

Am-214: 5.5 MeV alpha rays, 59.5 keV X-rays

X-ray(59.5 keV) / Alpha (5.5 MeVee) ratio

0.055/0.051 ~ 1.07 : ~7% difference

SN001

SN002

SN003

A c-axis 0.056 0.057 0.056 B b-axis 0.051 0.052 0.051 C c-axis 0.057 0.058 0.055 D b-axis 0.051 0.052 0.051 E a-axis 0.057 0.058 0.055 F a-axis 0.056 0.056 0.056

Approx.a surface

Approx.c surface b surface

α [deg.] β [deg.] γ [deg.]90.0000 90.6210 90.0000

59.5keV

anisotropic

c.f. 30-50% (DAMA)

• Assuming 7% difference @5keV• Including atmospheric ν & DSNB BG

10 tons for 1000 days

Expected “diurnal modulation”

c axis // North-Southc axis // East-West

c.f. Proton decay22.5 ktons x 6000 days

Which characters are related to the anisotropic property?

• Unit cell ?• Crystal structure : monoclinic?• Birefringence?• Emission center :(WO)6+ ?• Others…

Which characters are related to the anisotropic property?

• Unit cell ?• Crystal structure : monoclinic?• Birefringence?• Emission center :(WO)6+ ?• Others…

Monoclinic crystal system

Crystal structure of ZnWO4

Schofield et al., ActaCrystallographica, Section B: Structural Science (1997) 53,

p102-p112

α [deg.] β [deg.] γ [deg.]90.0000 90.6210 90.0000

Space Group P 2/ca [Å] b[Å] c[Å]4.69060 5.71820 4.92690

Atuchin + CGD 2011

When lattice constants change,anisotropic property change?

ZnWO4 (Zn, Mg)WO4

As grown crystal

(Zn0.95 Mg0.05)WO4

(Zn, Mg)WO4

ZnWO4

Powder X-ray diffraction to check the single crystal phase

device：BURKER D8 DISCOVERX-ray target： Cu-KαVoltage 40 kV, current: 40 mA

・We verify the single phase・Mg-doping: peak shift: consistent

(Zn, Mg)WO4

ZnWO4011

110

1-1-

1

111

020

020

111

1-1-

1

021

002

200

121

302

220

112

030

130

221

222

132

141

041

ZnWO4 (Zn, Mg)WO4

a 4.6937(15) 4.6929(10) No changeb 5.7197(18) 5.7155(12) became smallerc 4.9275(16) 4.9303(11) became biggerβ 90.638(4) 90.643(3) No change

Shift of Lattice constant (Unit cell)

a-surfaceVerification of orientation

a

c

b

βα

γ

b-surface c-surface

Using the powder X-ray diffraction data

Laue image

Mg-doping(replacing): Shift to cubic

X-ray(59.5 keV) / Alpha (5.5 MeVee)

• Light output: around 75% of that of ZｎWO4

• X-ray / Alpha ratio (compared to b surface)~1.02 （~ 0.050/0.048）ZnWO4:~1.07

anisotropic property became smalleras Mg doping

(Zn, Mg)WO4

ZnWO4

w/oMg

w/Mg

A c-axis 0.056 0.050 B b-axis 0.051 0.048C c-axis 0.057 0.051 D b-axis 0.051 0.048 E a-axis 0.057 0.050 F a-axis 0.056 0.049

X-ray / Alpha (59.5 keV/5.5 MeVee) ratio

Which characters are related to the anisotropic property?

• Unit cell : related?• Crystal structure : monoclinic?• Birefringence?• Emission center :(WO)6+ ?• Others…

Birefringence

0.055/0.051 ~ 1.07 : ~7% difference

CB

Black line

Optical Digital camera

paper

b-axis

b-surface

ZWO

Other Crystals, Same Crystal Structure

Ce: (La, Gd)2Si2O7 (Ce:La-GPS) : Monolithic, birefringence

a

c

b

βα

γ

Unit cell parametersa [A] 5.3905(8)b [A] 8.5605(11)ｃ [A] 13.957(2)β [deg.] 112.223(6)

2 inch

Light output @ RT: 40,000 ± 2,000 photons/MeV

Energy resolution@RT：5.8 ± 0.2%（FWHM, 662 keV）

X-ray / Alpha (59.5 keV/5.5 MeVee) ratio : La-GPS

（”A”）

X-ray / Alpha

“A”-surface 0.031

Other “B” 0.032

Other “C” 0.031

X-ray / Alpha (59.5 keV/5.5 MeVee) ratio

“A”

Which characters are related to the anisotropic property?

• Unit cell : related?• Crystal structure : monoclinic: No• Birefringence：No• Emission center :(WO)6+ ?• Others…

CdWO4 and PdWO4

X-ray / Alpha (59.5 keV/5.5 MeVee) ratio : CdWO4

B surface~A surface~C-surface

(preliminary)

(5.5-MeV α

/ 59.5 keV γ)

~A 17.7±0.1

~B 19.0±0.1

~C 18.6±0.2

59.5 keVX-ray

5.5 MeV α

X-ray / Alpha (59.5 keV/5.5 MeVee) ratio : PdWO4

No difference(preliminary)

5.5 MeV α線

Tetragonal crystal system(Scheelite Type)

CaWO4BaWO4PbWO4

Monoclinic crystal system(Wolframite Type)

ZnWO4MgWO4CdWO4

Tungsten groups

Different dissonances for O-W bandsEmission Center：

(WO6)6-P. Yadav et al., Journal of Alloysand Compounds 726, pp.1014-1023, 2017.

Which characters are related to the anisotropic property?

• Unit cell : related?• Crystal structure : monoclinic: No• Birefringence：No• Emission center :(WO)6+ :• Others…

Dis-homogeneity (distortion) around emission center would be related.

SummaryIf “isotropic” scintillation materials are available, direction-sensitive scintillation detectors are expected to be realized (solid state: high detection efficiency, simple detector)

ZnWO4 and similar scintillation material group : candidate

• We grew ZnWO4 and (Zn, Mg)WO4 crystals by the Cz method with diameters of around 1-inch.

• “Isotropic” properties were confirm• Wolframite type would have such “isotropic” properties.

Future works

Light output should be improved (now: 25% Light output of NaI:Tl) co-doping technique ?

Thank you for your attention &We are looking forward to seeing you in Sendai(SCINT 2019, 29 September – 4 October)

See food

JapaneseSAKE

Some gardens

http://scint2019.imr.tohoku.ac.jp/

Vielen Dank für Ihre Aufmerksamkeit