2004/dec/12 lrt2004 @snolab low radioactivity in candles t. kishimoto osaka univ

2004/Dec/12 LRT2004 @SNOlab

Low Radioactivity in CANDLES

T. Kishimoto

Osaka Univ.


Double decay and CaF2 crystals

• Why 48Ca

• ELEGANTS VI and CaF2(Eu)

– Roll off ratio

– Radioactivity in CaF2(Eu)

• CANDLES and CaF2

– External BG rejection by pulse shape– Internal BG rejection by pulse shape

– Making low BG CaF2 crystals


Why 48Ca(ELEGANTS VI)

• 48Ca : Search for 0 decay– highest Q-value (4.27 MeV)

largest phase volume

least BG (<2.6 MeV, <3.3 MeV)

Natural abundance 0.187%

• 19F : Search for spin coupled Dark Matters

Isotope 48Ca 76Ge 82Se 100Mo 116Cd 136Xe 150Nd

Q-value (MeV)

4.27 2.04 3.00 3.03 2.80 2.48 3.37

G0v×10-25

(year-1eV-2)2.44 0.244 1.08 1.75 1.89 1.81 8.00


ELEGANT VI

~3.5kg 19F~6.4 g 48Ca

45mm3

5x5=25crystals


神岡

大塔コスモ観測所

大阪大学核物理研究センター

大阪大学理学部

5 03 9 .5 m

第一観測室第二観測室第三観測室

国道 168号線

西吉野村側

大塔村側

845m

The tunnel was constructed for railroad but never used.

ELEGANT VI

Oto Cosmo Observatory


Roll-off ratioCaF2(pure) as light guide

active shield against PMT

CaF2(Eu) is not transparent for U.V. light

PMT PMT

CaF2(Eu)n = 1.44CaF2(pure)

n = 1.47

Optical greasen = 1.47

Silicon oiln = 1.40

CaF2(Eu)

CaF2(pure)

CaF2(pure)


Roll-off ratio

ROLL-OFFRATIO

ArbitaryUnit

RIGHT(channel)LEFT(channel)

RL

RL

VV

VVR

PH(CaF2(Eu))=3~4 times PH(CaF2)


Limit for decay of 48Ca• Obtained spectrum NPA730 (2004)

215• 4.23 kg yr

TGV C.L.) (90% years105.1

ing BeijC.L.) (76% years105.921

2102/1

Tcf.

C.L.) % (90year 104.1

C.L.) % (68year 105.422

2202/1

T

Expected BG : 1.3 events (simulation)

0 events in 0 energy window

48Ca double beta decay

10 -1

1

10

10 2

10 3

2000 3000 4000 5000

Energy (keV)

coun

ts/2

0ke

V

no events in 0 window

(Q0=4.27 MeV)

T1/2 > 1.8× 1022 yr (90%C.L.)2(sim)

BG (sim)

0 window

eV 7.442.7 m

BG in Q value region is successive Decay of or


Radioactive Backgrounds92U

91Pa

90Th

89Ac

88Ra

87Fr

86Rn

85At

84Po

83Bi

82Pb

81Tl

80Hg

4. 47x10 yr

U238

9

24. 10 dTh234

6. 75 hPa234

2. 45x10 yr

U234

5

8. 0x10 yr

Th230

4

1. 60x10 yr

Ra226

3

3. 82 dRn222

3. 05 mPo218

26. 8 mPb214

19. 7 mBi214

164 sPo214

22. 3 yrPb210

5. 01 dBi210

138. 4 dPo210

Pb206

Stabl e

4. 20 4. 78

4. 69

4. 79

5. 49

6. 00 7. 69 5. 31

Q =0. 199

Q

3. 26Q

1. 16

Q

0. 046Q

0. 64

92U

91Pa

90Th

89Ac

88Ra

87Fr

86Rn

85At

84Po

83Bi

82Pb

81Tl

80Hg

Ra228

Th232

6. 13 hAc228

Th228

Ra224

55. 6 sRn220

0. 15 sPo216

10. 64 hPb212

60. 6 mBi212

0. 30 sPo212

Stabl ePb208

3. 053 mTl208

4. 01 5. 42

5. 69

6. 29

6. 78 8. 78

Q

0. 039

Q

2. 25

Q

0. 57

1. 41x10 yr10

5. 76 yr

1. 91 yr

3. 66 d

Q

2. 18

Q

4. 99

6. 05

64%

36%

(A) (B)


• U-series

hardware (second) trigger– time window : 9 – 499 sec.

• Ac-series

• Th-series– time window : 0.05 – 1.0 (0.5) sec.

sec) 3.164(

Pb Po Bi 21076872143270214

EE

msec) 781.1(

Pb Po Rn 21173862156819219 EE

sec) 145(0.

Pb Po Rn 21267792166288220 EE

Radioactive Contamination


0

20000

1000 2000CaF 2 -1

0

50

100

1000 2000CaF 2 -2

0

50

100

1000 2000CaF 2 -3

0

20

40

1000 2000CaF 2 -4

0

50

1000 2000CaF 2 -5

0

100

1000 2000CaF 2 -6

0

50

100

1000 2000CaF 2 -7

0

50

1000 2000CaF 2 -8

0

50

1000 2000CaF 2 -9

0

50

100

1000 2000CaF 2 -10

0

25

50

1000 2000CaF 2 -11

0

100

1000 2000CaF 2 -12

0

25

50

1000 2000CaF 2 -13

0

100

1000 2000CaF 2 -14

0

100

1000 2000CaF 2 -15

0

200

1000 2000CaF 2 -16

0

50

1000 2000CaF 2 -17

0

100

1000 2000CaF 2 -18

0

100

1000 2000CaF 2 -19

0

100

1000 2000CaF 2 -20

0

20

40

1000 2000CaF 2 -21

0

100

1000 2000CaF 2 -22

0

50

1000 2000CaF 2 -23

0

20

1000 2000CaF 2 -24

0

20000

1000 2000CaF 2 -25

time window : 0.05-1.0 sec

sec) 145(0.

Pb Po Rn 21267792166288220 EE


CaF2 # U-series Ac-series Th-series1 4582.1 691.6 3152.12 211.1 40.3 9.43 5.2 5.5 13.04 59.7 24.0 4.15 155.1 59.0 10.86 154.2 60.1 14.67 153.4 26.1 8.68 61.5 27.5 5.19 137.3 25.4 5.4

10 236.6 36.6 10.611 67.8 29.0 5.012 155.6 47.0 15.313 71.4 28.0 4.614 160.9 64.7 15.015 404.2 48.3 18.216 61.1 87.7 27.017 97.9 33.4 6.918 39.4 47.5 15.419 151.9 43.1 16.820 16.2 21.2 13.421 36.6 25.2 5.022 32.8 50.9 13.823 55.6 26.5 7.624 42.2 26.2 4.925 7574.9 959.4 4352.9

21 22 23 24 25

1 2 3 4 5

16 17 18 19 20

11 12 13 14 15

6 7 8 9 10

Contamination inside crystals

Average contaminationAverage contamination

( #2 ( #2 －－ #24 )#24 )

U – seriesU – series

1.11×101.11×10-3-3 Bq/kg Bq/kg

Ac – seriesAc – series

3.84×103.84×10-4-4 Bq/kg Bq/kg

Th – seriesTh – series

1.09×101.09×10-4-4 Bq/kg Bq/kg

1.25x10-5 = 1 ppt Th 0.1mBq=24.6ppt


• How to make Big Detector– CaF2(Eu): No (attenuation length ~13 cm)

– CaF2: Yes (attenuation length > 1 m)

• CANDLES (CAlcium fluoride for studies of Neutrino and

Dark matters by Low Energy Spectrometers)

Double beta decay

0.1 eV and furtherDM

annual modulation

～


10 × 10 × 10 cm3 CaF2 crystals (1000 cubes)

in liquid scintillator Vessel

3.2 t CaF2

48Ca

　 3.1 kg (natural) 　 30 kg (further big or enrich)

Currently we are makingCANDLES III200g 48Ca (60 crystals)

1. BG2. Energy resolution


External BG rejection by Pulse shape (CANDLES I)

CaF2(pure)

liquid ScintillatorPMT(5")× 4

Signal from Liquid scinti.

Signal from CaF2

1 sec decay time


Signal to Noise Separation

Signal from Liquid Scint.

Backgrounds

Signal from CaF2

total

Fa

st c

om

po

nen

t


Energy resolution (Light output)

Light yield

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.0 1.0 2.0 3.0 4.0 5.0

concentration (g/l )

arbi

trar

y un

it

Bis-MSB Dimethyl-POPOP

POPOP

C24H22 C26H20N2O2 C24H16N2O

2

absorption

347 nm 363 nm 362 nm

emission

426 nm 428 nm 418 nm

Q.E. 0.94 0.93 --

Liquid Scintillator wave length shifter


Two Phase System (1)

CaF2(Pure)

Concept of Method• WLS Phase

– M.O(100%)+PPO(0.3g/L)– 5~10mm in thickness

– Large conversion eff.

• Veto Phase– M.O.(80%)+P.C.(20%)+PPO(1.0g/L)

– Large light output

CaF2 Emission (~280nm)

Conversion by PPO(350~400nm)

PMT

propagate


Performance Test (WLS phase)Side View

9.14%(FWHM)

Energy (keV)

Cou

nts

Energy (keV)

60Co (1333keV)

5.91%(FWHM)

137Cs (662keV)

CaF2(pure)

Liquid Scintillator

Standard Source

CANDLES I with 10 cm cube CaF2(pure)

(WLS phase)


CANDLES III • Under Construction (Osaka Univ.)• CaF2(pure)

– 103 cm3 × 60 crystals total weight : 191 kg

• Liquid scintillator• 1000×h1000 acrylic container

– H2O Buffer passive shield• 　 00×h2800

– safety regulation• Purification system• PMTs

– 15” PMT (×19) : R2018– 13” PMT (×29) : R8055

13i nch PMT

H2O

CaF2( pur e)

15i nch PMT


Background – reduction / rejection – • Reduction of radioactive impurities inside crystal

• So Far…– Powder selection (3.2 kg x 11 crystals)

• U-chain (214Bi) 51 Bq/kg• Th-chain (220Rn)21 Bq/kg

CaF2(Eu)

214Bi 1110 Bq/kg

220Rn 98 Bq/kg

Raw MaterialsCaF2 powder Fused CaF2 CaF2 crystal(CaCO3, HF)

•Powder selection

•Rinse out the powder

(H2O, HNO3,…)

•Growing process

•Scavenger selection

… R&D study in progress

BG measurement at Oto

Enough for CANDELS III~30 Bq/kgAnother one order forCANDLES IV and further


Rejection by successive decay

60

80

100

120

140

160

180

200

220

100 200 300 400 500 600Time(ch/10nsec)

212 Bi or 214 Bi

Time Lag

212 Po or 214 Po

Flash ADC identifies

successive decay

No Reduction In ELEGANTS VI Currently 0.04 (20 nsec) Future 0.01 (5 nsec)

sec) (0.299

Pb Po Bi 20878.821225.2212

MeVEMeVE


Pulse Shape Discrimination(2)

• PSD by 100MHz FADC– rays from internal contamination– rays from 60Co standard source– fitting pulse shape with two exponential func. (fixed time constants)

– Ratio ; Afast/Aslow (Intensity Ratio of Fast and Slow Components)– Clear Discrimination between and () Events– Background Rejection Efficiency > 99%


H2O

15”PMT

Mount System

CaF2(Pure)10cm cube

Liquid Scintillator

CANDLES-II

• Prototype

45cm

Cosmic-ray Events (High Energy)

Index 1.44@586nm (CaF2)

Index 1.46@586nm (Mineral Oil)

S.Umehara


Mile stone

• ELEGANTS VI – running with new BG rejection (2)

• CANDLES I, II• CANDLES III

– 10cm3 cube (60 crystals) – ~30 Bq/kg for 0.5 eV

• CANDLES IV – 10cm3 cube (1000 crystals) 3.2t– ~5 Bq/kg for 0.1 eV

• CANDLES V – Several 10t or enrichment

2004/dec/12 lrt2004 @snolab low radioactivity in candles t. kishimoto osaka univ

Documents

liquid scintillator

expected bg

double decay

caf2external bg rejection

bg elegant vi

scintillation light

successive decay

t caf2