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Study of 48 Ca double beta decay with CANDLES. OGAWA Izumi ( 小川 泉 ) Osaka Univ. ( 大阪大学 ). Double beta decay of 48 Ca. Largest Q value (4.27 MeV) next largest; 150 Nd (3.3 MeV) large phase space factor almost background free ( g : 2.6 MeV, b : 3.3 MeV)

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study of 48 ca double beta decay with candles

Study of 48Ca double beta decay with CANDLES

OGAWA Izumi (小川 泉)

Osaka Univ.(大阪大学)

INPC2007

double beta decay of 48 ca
Double beta decay of 48Ca
  • Largest Q value (4.27 MeV)
    • next largest; 150Nd (3.3 MeV)
    • large phase space factor
    • almost background free (g: 2.6 MeV, b: 3.3 MeV)
  • Low Natural abundance → 0.187%
    • large detector
    • enrichment
  • Next generation detector
    • Mdet2if background free
    • Mdet4 if background limited

INPC2007

candles

Liquid Scintillator

(Veto Counter)

CaF2(Pure)

Buffer Oil

Large PMT

CANDLES
  • undoped CaF2 (CaF2(pure))
    • 48Ca (Qbb=4.27 MeV)
    • 300 kg 3 t 100 t
  • Liquid Scintillator (LS)
    • 4p active shield
    • Passive shield
    • wavelength shifter for CaF2
  • Photomultiplier
    • large photo-caoverage

CAlcium fluoride for studies of Neutrino and Dark matters

by Low Energy Spectrometer

INPC2007

candles i pop proof of principle detector
CANDLES I - POP (Proof of Principle) Detector
  • CaF2(pure) crystal

in liquid scintillator

(with w.l. shifter)

viewed by 4 PMTs (5 inch)

  • LS : mineral oil

+ DPO (3 g/l)

+ Bis-MSB (0.3 g/l)

4p active shield

INPC2007

performance test 4 p active shield
Performance Test (4p active shield)

2 ADCs with

different gate width

40K

events from LS

events from CaF2

Clear separation between CaF2 and LS

INPC2007

energy resolution
Energy resolution

137Cs (662 keV)

9.14%(FWHM)

Standard g Source

CaF2(pure)

Counts

Side View

wavelength shifter

Energy (keV)

60Co (1333 keV)

CANDLES I with 10 cm3 CaF2(pure)

  • Energy Resolution:
  • 9.1 %(FWHM) at 662keV
  • 3.4 % (FWHM)at 4.27MeV
  • Req. for CANDLES III ; 4.0 %

5.91%(FWHM)

Energy (keV)

INPC2007

radioactive bg inside caf 2
Radioactive BG inside CaF2
  • Natural Radioactive BGs ~Qbb
    • Maximum energy
      • g~ 2.6 MeV, b~3.3 MeV, a(max)~2.7 MeVe.e. (quench;fa~ 0.3)
    • Successive decays of a, b, gin decay chain
      • ~1 msec decay time CaF2

Pulse shape

Emax=5.8MeV(U)

5.3MeV(Th)

b +a

INPC2007

development of high purity caf 2 crystals
Development of High Purity CaF2 Crystals
  • CaF2(Eu) in ELEGANT VI
  • U-chain(214Bi) :1100 mBq/kg
  • Th-chain(220Rn) : 98 mBq/kg

U and Th

(ICP-MS)

CaF2

Powder

Fused

CaF2

CaF2

Crystal

Raw Materials

CaCO3, HF

Radioactivities in CaF2 Powder

(HPGe measurement)

Radioactivities in CaF2(pure) Crystal

(a-ray measurement)

Powder selection

Crystal growing

101 crystals

  • U-chain(214Bi) ~36 mBq/kg …1/30 of Previous Crystals (14±5 mBq/kg ;Best)
  • Th-chain(220Rn) ~29 mBq/kg …1/3 of Previous Crystals ( 6±1 mBq/kg ;Best)

INPC2007

rejection of double pulse
Rejection of Double Pulse

Typical Pulse Shape (500 MHz FADC)

pulse height (ch)

pulse height (ch)

8.8ns

810ns

Delayed

Prompt

time(2 nsec)

time(2 nsec)

recorded shape

fitted shape

99% of double pulse events will be rejected

INPC2007

pulse shape discrimination
Pulse Shape Discrimination
  • Pulse Shape discrimination
    • Shape Indicator (PRC 67(2003) 014310)

Difference in decay shape

betweenaandgrays

a-event

g-event

1s

mean value:

no energy dependence (>1 MeV)

~99.7% reduction at Q-value

INPC2007

candles iii
CANDLES III
  • CANDLES III (U.G.) ‘Sanchika’
    • Kamioka
  • CANDLES III (prototype)
    • @Osaka University
    • R&D

INPC2007

candles iii u g
CaF2(pure)

103 cm3 × 96 crystals; 305 kg

Liquid scintillator

two phase system

Purification system

H2O Buffer

passive shield

PMTs

17” PMT (×14) : R7250

13” PMT (×56) : R8055

mirror type reflector

photon trans. simulation

energy res. ~3.5 % @ Qbb

Kamioka underground lab.

CANDLES III(U.G.)

INPC2007

candles iii prototype
CANDLES III (prototype)
  • Constructed at Osaka Univ. (sea level)
    • small version for R&D
    • check the performance of CANDLES
  • CaF2 modules
    • 103 cm3 × 60 crystal; 191 kg
    • with conversion phase
  • Liquid scintillator
    • f1000×h1000 acrylic container
  • H2O Buffer : passive shield
    • f2800×h2600
  • PMTs
    • 15” PMT (× 8) : R2018
    • 13” PMT (×32) : R8055

1 dirty crystal

U:65 mBq/kg, Th:28 mBq/kg

33.4% photo-coverage

INPC2007

candles iii prototype1
CANDLES III (prototype)

h2.6 m

f 2.8 m

INPC2007

slide15
PMTs
  • Inside view

Photomultiplier Tube (13inch)

INPC2007

caf 2 module
CaF2 module
  • CaF2 + conversion phase + acrylic case

filled

half filled

Index [email protected] (CaF2)

Index [email protected] (Mineral Oil)

INPC2007

ls tank
LS tank
  • 58 CaF2 modules installed

INPC2007

conclusion
Study of 48Ca double beta decay

Largest Q value

CANDLES system (CaF2 in L.S.)

CANDLES III (prototype)

58 CaF2 modules installed

R&D using prototype detector at Osaka University.

CANDLES III (U.G.)

Design study

expected BG: 0.14 events/year

Construction at Kamioka will start in spring 2008

Conclusion

INPC2007

mile stone
Mile stone
  • CANDLES I, II, POP
  • CANDLES III (prototype)
    • CaF2 (10cm3) 191 kg
  • CANDLES III (U.G.)
    • Kamioka underground lab. (spring 2008)
    • CaF2 300 kg ~30 Bq/kg for ~0.5 eV
  • CANDLES IV
    • 3 t; Kamioka
    • ~3 Bq/kg for ~0.1 eV in 6 yrs
  • CANDLES V
    • 100 t; Kamland or ??? for ~30 meV in 7 yrs
    • another option; enrichment

INPC2007

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