2004/dec/12 lrt2004 @snolab low radioactivity in candles t. kishimoto osaka univ
TRANSCRIPT
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2004/Dec/12 LRT2004 @SNOlab
Low Radioactivity in CANDLES
T. Kishimoto
Osaka Univ.
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
ELEGANT VI
~3.5kg 19F~6.4 g 48Ca
45mm3
5x5=25crystals
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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)
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2004/Dec/12 LRT2004 @SNOlab
Roll-off ratio
ROLL-OFFRATIO
ArbitaryUnit
RIGHT(channel)LEFT(channel)
RL
RL
VV
VVR
PH(CaF2(Eu))=3~4 times PH(CaF2)
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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)
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2004/Dec/12 LRT2004 @SNOlab
• 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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
• 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
~
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
Signal to Noise Separation
Signal from Liquid Scint.
Backgrounds
Signal from CaF2
total
Fa
st c
om
po
nen
t
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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)
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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%
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2004/Dec/12 LRT2004 @SNOlab
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
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2004/Dec/12 LRT2004 @SNOlab
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