1 study of 48 ca double beta decay by candles t. kishimoto osaka univ
DESCRIPTION
Double Beta Decay of 48 Ca Studied by ELEGANT VI keV 0.63 y BG (sim) 2 (sim) 0 window NPA 730 ’04, 215 Not limited by backgrounds 1.76 y Yet no BG But only 6.4g of 48 CaTRANSCRIPT
1
Study of 48Ca Double Beta Decay by CANDLES
T. KishimotoOsaka Univ.
2
Why 48Ca• Highest Q value (4.27 MeV)
– next largest 150Nd (3.3 MeV)– Large phase space factor – Little BG ( natural radioactivity : 2.6 MeV, : 3.3 MeV )
• Natural abundance: 0.187%– Huge amount of CaF2 crystals– Isotope separation: expensive (no Gas) – Early studies (recent studies use separated isotope)
• Next generation – M ~ T-1/2 ~ M-2 (no BG)
~ M-4 ( BG limited )C.L.) % (90 eV 7.44~2.7m
NPA 730 ’ 04, 215
48Ca (no BG)
Double Beta Decay of 48Ca Studied by ELEGANT VI
4104 - 4438 keV
0.63 y
48Ca double beta decay
10 -1
1
10
10 2
10 3
2000 3000 4000 5000Energy (keV)
coun
ts/2
0ke
V
no events in 0 window
(Q0=4.27 MeV)
T1/2 > 1.8× 1022 yr (90%C.L.)
BG (sim)
2(sim)
0 window
C.L.) % (90year 104.1 2202/1 T
C.L.) % (90 eV 7.44~2.7m
NPA 730 ’ 04, 215
Not limited by backgrounds
1.76 y
Yet no BG
C.L.) % (90 eV 7.21~5.3m
But only 6.4g of 48Ca
4
CANDLES
CaFCaF22(Pure)(Pure) 200kg, 300kg, 3t,30t(2%) 48Ca (200g, 300g, 3kg, 300kg)
Liquid ScintillatorWave Length Shifter4 Active ShieldPassive shield
PhotomultiplierPhotomultiplier energy resolution
CaF2(Pure)
Liquid Scintillator(Veto Counter)
Buffer Oil
Large PMT
CAlcium fluoride for studies of Neutrino and Dark matrtersby Low Energy Spectrometer
21COE Sep 11, Osaka
5
CANDLES IRejection of ext. BG
Liquid Scintillator
CaF2
ADC(fast)ADC(total) CaF2(pure)
liquid ScintillatorPMT(5")× 4
ADC(total)
Liquid Scintillator
CaF2
CANDELS IPOP detector
Background @ Q value region• No natural BG @ ~4 MeV
– Maximum energy• ~ 2.6 MeV, ~3.3 MeV, ~2.5 MeV(quench~0.3)
– Successive decay of • ~1sec decay time
100MHz FADC T > 30ns(3ch) ; ~5% 500MHz FADC (under preparation) T > 5ns ; ~1%
212Bi ()
212Po ()
Pulse shape
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Pulse Shape Discrimination
• PSD (Event by Event)PSD (Event by Event)– FADC (100MHz)– Afast/Aslow (Fast and slow component)
Difference in decay time between and rays
Discrimination between and Events Background Reduction ~ 0.3%
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Development of Low Radioactive CaF2
• delayed coincidence• @ Oto Cosmo observatory
0
5
10
15
20
25
30
35
40
45
50
0 - 0.01
- 0.02
- 0.03
- 0.04
- 0.05
- 0.06
- 0.07
- 0.08
- 0.09
- 0.10
- 0.12
- 0.14
- 0.16
- 0.18
- 0.20
(mBq/kg)不純物濃度
個数 U系列
Th系列
U~36Bq/kg14 (best)
Th~20Bq/kg6 (best)N
umbe
r of C
aF2 c
ryst
als
mBq/kg
95 crystals
3t 600k 300k
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Energy resolution and BG rejection (2 phase)
CaF2(Pure)
• CaF2: UV region (PMT)• Conversion layer
– UV→visible (PMT)– UV transparent
• Veto layer– Liq scint : absorb UV
CaF2 Emission (~285nm)
Conversion by WLS(350~400nm)
PMT
propagate
9.14%(FWHM)
Energy (keV)
Cou
nts
137Cs (662keV)
21COE Sep 11, Osaka
10
CANDLES III (prototype)
10cm3 x 56 CaF200×h2600
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CANDLES IIIInside ViewInside View Photomultiplier Tube(13inch)
Tank for Liquid Scintillator (Acrylic Case)40 PMTs Version
Buffer water
Test measurement just started @ Osaka (sea level)
2007/03/25 日本物理学会春の大会@首都大学東京
Crystal with huge BG
1st 2nd
3rd 4th 5th
no crystals
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Mile stone• ELEGANTS VI
– running with new BG rejection (2)• CANDLES I, II• CANDLES III
– 10cm3 cube (100 crystals) ~0.5 eV– BG of CaF2 ~30 Bq/kg (<100 Bq/kg )
• CANDLES III(UG) • CANDLES IV
– 10cm3 cube (1000 crystals) 3.2t– BG of CaF2 ~10 Bq/kg for 0.2 eV – Kamioka
Achieved Kamioka
DUSEL town meetingNov. 2-4, Washington DC
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CANDLES
XMASS
SK
KamLand
New experimental Hall under excavation
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Future
• CANDLES V to sense ~10 meV region – ~30 ton CaF2 and 2% enrichment– Further large space
• Kamland, SNO (Vessel and PMT’s)• DUSEL
• Isotope enrichment– Available: 76Ge, 100Mo, 128Te– exception: 48Ca, 150Nd
• R&D in progress– Crown ether (Resin is made)
• Current separation constant is a bit low.