CANDLES for the study of 48Ca double beta decay - LRT2006

lrt2006.in2p3.fr

CANDLES for the study of 48Ca double beta decay - LRT2006

LRT2006 Oct 1-4,

Aussosis - France

CANDLES for the study of 48 Ca

double beta decay and low

radioactivity CaF 2 crystals

T. Kishimoto

Osaka Univ.

1


LRT2006 Oct 1-4,

Aussosis - France

Why 48 Ca

• Highest Q value (4.27 MeV)

– next largest 150Nd (3.3 MeV)

– Large phase space factor

– Little BG(natural radioactivity γ: 2.6 MeV, β: 3.3

MeV)

• Natural abundance: 0.187%

– Isotope separation: expensive (no Gas)

– Early studies (recent studies use separated isotope)

• Next generation

–M ν ~ T -1/2 ~ M -2 (no BG)

~ M -4 (BG limited)

– 48 Ca (no BG)


< 7.

2

~

44.

7

eV

NPA 730 ’04, 215

(90 %

C.L.)

2


LRT2006 Oct 1-4,

Aussosis - France

How to sense m ν=10 -(1~2) eV

• Big detector

– Huge amount of materials

• Low radioactive background

– Active shield

– Passive shield

– Low background material

– BG rejection by signal processing

• High resolution

– Backgrounds from 2νββ decay

CANDLES is our solution

3


LRT2006 Oct 1-4,

Aussosis - France

CANDLES

CAlcium fluoride for studies of Neutrino and Dark matrters

by Low Energy Spectrometer

Liquid Scintillator

(Veto Counter)

CaF 2 (Pure)

Buffer Oil

Large PMT

CaF 2(Pure) (Pure)

200kg, 300kg, 6t,100t

48 Ca (200g, 300g, 6kg, 100kg)

Liquid Scintillator

Wave Length Shifter

4 π Active Shield

Passive shield

Photomultiplier

energy resolution

4


• Big detector

LRT2006 Oct 1-4,

Aussosis - France

CaF 2 crystal

– Best optical lens

– Long attenuation length

• 10m (catalog value for visible light)

• >1m (our measurement for scintillation light)

CANDLES IV

– 15x15x15 cm3 x 600 (6t)

– Increase the number of nuclei ( 48Ca) 6.4 g (ELE VI) ~6(kg)

22

8.

1 × 10 atoms

10 atoms

6 2

`

5


LRT2006 Oct 1-4,

Aussosis - France

CANDLES I

POP (Proof of Principle) Detector

CaF2 (pure) crystal

in liquid scintillator

(with w.l. shifter)

viewed by 4 PMTs (5 inch)

liq. scint. : mineral oil

+ DPO (3 g/l)

+ Bis-MSB (0.3 g/l)

PMT(5")~ 4

liquid Scintillator

CaF2(pure)

6


LRT2006 Oct 1-4,

Aussosis - France

Signal discrimination

ADC(fast)/ADC(total)

Liquid Scintillator

CaF 2

Decay time

Liq. Scinti

~10 nsec

CaF 2

~1 μsec

~1 liquid scintillator

~0.04 CaF 2

7


ADC(fast)/ADC(total)

LRT2006 Oct 1-4,

Aussosis - France

Signal discrimination

ADC(total)

57Co Co source

Signal from Liquid

scintillator

CaF 2

8


LRT2006 Oct 1-4,

Aussosis - France

Background @ Q value region

• No natural BG @ ~4 MeV

– Maximum energy

• γ~ 2.6 MeV, β~3.3 MeV, α~2.5 MeV(quench~0.3)

– Successive decay of α β γ

•~1μsec decay time

Pulse shape

β+α

Gate width(4μsec )

E max =5.8MeV(U)

5.3MeV(Th)

Counts(/20keV)

10 2

10

1

10 -1

10 -2

212 Bi

208 Tl

214 Bi

experimental Data

2νββ

0νββ Window

2000 2500 3000 3500 4000 4500 5000

Energy(keV) 9


Pules Height(CH/10mV/MeV)

100

80

60

40

20

LRT2006 Oct 1-4,

Aussosis - France

Rejection of Double Pulse

Typical Pulse Shape(100MHz FADC)

900ns

0

0 50 100 150 200 250 300 350 400

Prompt

Q β = 3.27MeV

212 Bi

64%

Q β = 2.25MeV

Delayed

Time(10nsec)

Q α = 7.83MeV

β α

212 Po

T 1/2 = 0.299μsec

Q α = 8.95MeV

Pules Height(CH/10mV/MeV)

120

100

80

60

40

20

0

0 50 100 150 200 250 300 350 400

Time(10nsec)

0

-10 -5 0 5 10 15 20

Reduction

100MHz FADC ΔT > 30ns(3ch) ; ~5%

500MHz FADC (under preparation) . . . ΔT > 5ns; ~1%

Pules Height(CH/10mV/MeV)

120

100

80

60

40

20

50ns

Time(10nsec)

10


LRT2006 Oct 1-4,

Aussosis - France

Pulse Shape Discrimination

Difference in decay time

between α and γ rays

• PSD (Event by Event)

– FADC (100MHz)

– Afast /Aslow (Fast and slow component)

PSD between γ and α rays

Discrimination between α and γ(β) Events

Background Reduction ~ 0.3%

As Af γ-ray Event α-ray Event

Slow

Fast

Af/As = 0.5(γ-ray) Af/As = 1.0(α-ray)

11


LRT2006 Oct 1-4,

Aussosis - France

Development of High Purity

CaF 2 Crystals

CaF2(Eu) in ELEGANT VI

U-chain( 214Bi) :1100 μBq/kg

Th-chain( 220 U and Th

(ICP-MS)

Rn) : 98 μBq/kg

Raw Materials

CaCO 3 , HF

Radioactivities in CaF 2 Powder

(HPGe measurement)

96 crystals

CaF 2

Powder

Fused

CaF 2

Radioactivities in CaF 2(pure) Crystal

(β−α delayed coincidence)

Powder selection

Crystal growing

U-chain( 214Bi) ~36 μBq/kg …1/30 of Previous Crystals

Th-chain( 220Rn) ~28 μBq/kg …1/3 of Previous Crystals

CaF 2

Crystal

12


LRT2006 Oct 1-4,

Aussosis - France

Radioactivities in CaF 2

• β−α, α−α delayed coincidence

• @ Oto Cosmo observatory

Number of CaF 2 crystals

50

45

40

35

30

25

20

15

10

5

0

0 - 0.01

- 0.02

- 0.03

- 0.04

- 0.05

- 0.06

- 0.07

- 0.08

- 0.09

(m Bq/kg)

- 0.10

- 0.12

- 0.14

mBq/kg

- 0.16

- 0.18

- 0.20

U

Th

95 crystals

U~36μBq/kg

14 (best)

Th~20μBq/kg

6 (best)

13


LRT2006 Oct 1-4,

Aussosis - France

Energy resolution of CaF 2

• Energy Resolution

• Scintillation light

– ~0.5 of CaF2 (Eu) (quart window PMT)

– peak emission U.V. (285 nm)

• Increase # of photons

– Wavelength shifter

– UV visible light

ΔE

~

1

N

p

14


LRT2006 Oct 1-4,

Aussosis - France

Two Phase System

Concept of Method

• Conversion Phase

– Large conversion eff.

– good transparency for UV

• Veto Phase

– Large light output with

aromatic solvent

CaF 2 Emission (~285nm)

Conversion by WLS(350~400nm)

propagate

PMT

UV light

CaF 2 (Pure)

Visible light

High resolution and

High veto efficiency

15


Energy resolution

Side View

CANDLES I with

10 cm 3 CaF 2 (pure)

LRT2006 Oct 1-4,

Aussosis - France

Standard γ Source

CaF 2(pure)

Liquid Scintillator

(WLS phase)

~1 ph/keV

Energy Resolution:

9.1%(FWHM) at 662keV

=3.4% (FWHM) at 4.27MeV

Req. for CANDLES III ; 4.0%

Counts

1500

1250

1000

750

500

250

0

3000

2500

2000

1500

1000

500

0

137 Cs

(662keV)

9.14%(FWHM)

0 200 400 600 800 1000

60 Co (1333keV)

Energy (keV)

5.91%(FWHM)

0 250 500 750 1000 1250 1500 1750

Energy (keV)

16


• Prototype

LRT2006 Oct 1-4,

Aussosis - France

CANDLES-II

Index 1.44@586nm (CaF 2 )

Index 1.46@586nm (Mineral Oil)

1

0.75

0.5

0.25

0

-0.25

-0.5

-0.75

45cm

Liquid Scintillator

CaF2(Pure)

10cm cube

Mount System

-1

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1

300

250

200

150

100

50

H 2 O

15”PMT

Cosmic-ray Events (High Energy)

0

-1 -0.75 -0.5 -0.25 0 0.25 0.5 0.75 1

S.Umehara

17


LRT2006 Oct 1-4,

Aussosis - France

CANDLES III

• Construction almost completed @ Osaka Univ.

• CaF 2 (pure)

– 60×10 3 cm 3 ; 191 kg

• Liquid scintillator

– φ 1m× h 1m acrylic container

• Purification system

• H 2 O Buffer: passive shield

– φ 2800× h 2600

– safety regulation

• PMTs

– 15” PMT (×8) : R2018

– 13” PMT (×32) : R8055

13i nch PMT

15i nch PMT

H2O

CaF2(pure)

18


LRT2006 Oct 1-4,

Aussosis - France

CANDLES III (prototype)

φ 2.8 m

h 2.6 m

19


LRT2006 Oct 1-4,

Aussosis - France

Inside View

CANDLES III

Photomultiplier Tube(13inch)

40 PMTs Version

Tank for Liquid Scintillator

And 60 PMTs Version . . . Funded

(Acrylic Case)

20


LS tank

•4 CaF 2 modules

installed

LRT2006 Oct 1-4,

Aussosis - France

Access port for calibration

21


LRT2006 Oct 1-4,

Aussosis - France

CaF 2 module

•CaF 2 + conversion phase + acrylic case

half filled

filled

Index 1.44@586nm (CaF 2 )

Index 1.46@586nm (Mineral Oil)

22


LRT2006 Oct 1-4,

Aussosis - France

CANDLES III(U.G.)

san-chika

• CaF 2 (pure)

– 10 3 cm 3 × 96 crystals; 305 kg

• Liquid scintillator

– two phase system

– Purification system

• H 2 O Buffer

– passive shield

• PMTs

– 17” PMT (×14) : R7250

– 13” PMT (×56) : R8055

– mirror type reflector

• photon trans. simulation

energy res. ~3.5 % @ Q ββ

• Kamioka underground lab.

pure

water

LS

Reflector

CaF 2

w.l. shifter

23


LRT2006 Oct 1-4,

Aussosis - France

Liquid Scintillator

(Veto Counter)

CaF 2 (Pure)

Buffer Oil

CANDLES IV

Large PMT

15×15×15 cm3 CaF2 (600 cubes) 6.4 t

liquid scintillator Vessel

( 48Ca) 6.4 kg

1. BG (~3μBq/kg Th)

1. Needs R&D

2. Current best

~6μBq/kg

2. Energy resolution

1. Photo coverage

24


LRT2006 Oct 1-4,

Aussosis - France

Mile stone

• ELEGANTS VI

– running with new BG rejection (2ν)

CANDLES I, II

CANDLES III

– 10cm 3 cube (100 crystals) ~0.5 eV

– BG of CaF 2 ~30 μBq/kg

CANDLES III(UG)

CANDLES IV

– 15cm 3 cube (600 crystals) 6t

– BG of CaF 2 ~3 μBq/kg for 0.1 eV

–Kamioka

Achieved

Kamioka

25


LRT2006 Oct 1-4,

Aussosis - France

Future

CANDLES V to sense 30 meV region

– ~100 ton CaF2

– Can be installed in

• Kamland

•SNO

• Isotope separation

– Available: 76Ge, 100Mo, 128Te – exception: 48Ca, 150Nd (feasible?)

•R&D

– Crown ether, centrifuge, others

• If 2%: 10 meV region

Vessel and PMT’s

26

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