1. Activities on double beta decay search at KIMS
Double beta decay search with HPGe & CsI(Tl)
Metal Loaded Liquid Scintillators
EC/b+, b+b+ search with 4p CsI(Tl) shielding
Prospect
H.J.Kim (KyungPook National Univ.)
for KIMS
International Workshop on Double Beta Decay Searches, 2009/10/15-17

2. 0-, 2-n bb decay 2-n bb decay 2nd order beta decay Rare nuclear decay
(>1018 years)
0-n bb decay
n mass>0 &
Majorana particle
2) New Physics e ν N N’
2νββ e ν N N’
0νββ A B

3. Double beta decay process
(A,Z+1)
(A,Z-1)
(A,Z)
(A,Z)
(A,Z+2)
(A,Z-2)
(A,Z) -> (A,Z+2) + 2b +2n (A,Z) -> (A,Z-2) + 2b+ +2n
EC+b+ ,2EC also is possible
Excited state g
b+ -> g g (511 keV)
Ground state

4. Environment Parameters in Y2L
Gneiss (2 Gyr )
Depth
Minimum 700 m
Temperature
20 ~ 25 oC
Humidity
35 ~ 60 %
Rock contents
238U less than 0.5 ppm
232Th ppm
40K ppm
Muon flux
2.7 x 10-7 /cm2/s
Neutron flux
8 x10-7 /cm2/s
222Rn in air
1~2 pCi/liter

5. R&D and experiment of bb decay at KIMS
Double beta experiment and R&D (9 years)
<= Developing new experimental method with affordable cost
Experiment with HPGe + CsI : Sn, 64Zn limit
Currently working on 0n-EC/EC resonance and EC/b+, b+b+ search with HPGe: 136Ce, 130Ba
Sn-loaded liquid scintillator : 124Sn limit (new method for bb )
b+b+, EC/b+ experiment with 4p CsI(Tl) shielding
-> on going with CaMoO4 (J.I.Lee’s talk)
-> SrCl (J.H.So’s talk)
CaMoO4 R&D: (new crystal for bb )
-> 1’st experiment soon (Tomorrow talks)

6. Why HPGe for DB search? Advantage
a) Very good energy resolution : ~1-2 keV FWHM
b) It is possible to setup ultra-low background HPGe
c) Well known technology
Disadvantage
a) Low gamma efficiency (Low Z)
a) Passive method
b) Only possible for excited transition or b+, EC decay
Y2L
a) 100% low background HPGe available
b) Ultra-low background planer type was being ordered.
* Method : HPGe, HPGe+ CsI(Tl), HPGe+Scintillator(DB)

7. Low background HPGe at Y2L
Shielding : 5 cm OFHC Cu +
15 cm Pb +N2 gas flowing
Ultra low background measurement,
Double beta decay search
Normal Water
Ultra pure
Pure water
NIMA 552(2005) 456

8. Sn-124, Sn-122 0-,2-n bb excited state transition limit
* World best limit on Sn-124 (E.Norman PLB 195,1987)
Test of TBSN for a week
450cm3 HPGe, 140 hours , 1.0liter TBSN : 400g of Sn
2+ (603keV) 3.8x1018 year (4.0x1019 year)
0+ (1156) x1019 year (2 -n theory : 2.7x1021)
0+ (1326) x1019 year (2.2x1018 year)
* Sn-122 EC+b+ decay ; 1.5x1018 year (6.1x1013)

9. Sn-112 EC+b+ (b+-> 2g)

10. Positve evidence by I.BIKIT et.al, App. Radio. Isot. 46, 455, 1995
Zn EC+b+ decay
EC+b+ limit ( b+ -> 2 g decay)
99.7% CL
Positve evidence by I.BIKIT et.al,
App. Radio. Isot. 46, 455, 1995
<= 25% HPGe + NaI(Tl) with 350g Zn at surface with shielding.
-> Need to confirm or disprove!

11. Zn EC+b+ decay 511keV g CsI 7.5x7.5x8 Zn 511keV g HPGe
HPGe + Zn(8x8x1cm)+CsI(Tl) crystal
Our advantage:
100% of HPGe
350m underground
10cm low background lead,
10cm copper and N2 flowing
Calibration by Na22 (b+ radioactive source)
Efficiency calculation by Geant4; 3%
Very Preliminary result with 1 week data;
Coincidence cut with 2 sigma range ; 1 event
2x1020 year by 95% CL
If I.BIKIT’s central value is taken, we would observe 100 events (1.1x1019 y)
H.J.Kim et al., Nuclear Physics A 793 (2007)
511keV g
CsI
7.5x7.5x8 Zn
511keV g
HPGe

12. 511keV Efficiency of Zn, Sn Zn Sn

13. Energy dist. at CsI crystal

14. Energy dist at HPGe

15. Resonance ECEC process

16. 136Ce->136Ba 2392, 2400 0n ECEC resonance

17. Current limit on 136Ce b+b+, b+/EC, ECEC
Q value = 2400 keV
Natural abundance = 0.185%
* No excited transition has been studied !

18. Experimental method & expectation
HPGe + CeO2 powder in Marinelli beaker : days, 1.25 kg data taking
HPGe + Ba(No3)2 powder in Marinelli beaker : days, 1.5 kg data taking
Sensitivity : 0.002% Ce-142, 3% full peak eff, 1month => ~1018 years
Expectation : 136Ce, 130Ba
1)Improved b+b+, b+/EC limit
2) Study of b+b+, b+/EC excited transition
3) First study of 0n ECEC resonance transition
* CeBr3 crystal (or Cs2LiCeCl6) for 0,2n ECEC or double coincidence study later

19. Why metal loaded liquid scintillator?
Advantage
a) high-Z can be loaded to LS (>50% or more)
b) Fast timing response (few ns)
c) Low cost of LS, Large volume is possible
d) U/Th/K background for LS is low and purification
is known
e) Some DB elements can’t be made to Scintillator
Disadvantage
a) Bigger volume is necessary (C,H in LS, low density)
b) Lower light output (>15% of NaI(Tl))

20. LSC test sample
HV + LSC
Setup
VME

21. Zr2EH + LSC (50% ->Zr 3%) Nd2EH + LSC (50%->Nd 6.25%)
TetraButhyl Tin + LSC (50%->Sn 20%)
TetraMethyl Tin + LSC (50%->Sn 40%)

22. Tin-loaded LSC for 0n-bb search
Double betat decay search with 124Sn
Q = 2287 keV
5% of natural abundance
Y2L facility can be used for the experiment

23. Tin-loaded LSC for 0n-bb search
NIMA 570 (2007) 454
1.1 liter of TLSC
33% of Sn
Tl MeV g
4.3% s

24. 214Bi b-decay g 214Po a-decay -> T 1/2 = 0.169ms (0.163 ms exp.) :
U-238 decay chain : mBq/kg background

25. 212Bi b-decay g 212Po a-decay -> T 1/2 = 301ns (300ns exp);
Th-232 Decay chain : mBq/kg

26. 0n bb search with Sn-loaded LSC
1.1 liter 33% Tin-loaded Liquid scintillator
9 Month data at Y2L inside of Pb shielding
Astro. Part. Phys. 31 (2009) 412
T1/2 < 2.4x1017 yr at 90% C.L
T1/2 < 2.0x1019 yr at 90% C.L
2287keV

27. Conceptual design of Metal-loaded LSC
Nd/Cd/Gd
Loaded LSC
Mineral
oil
acryl
Muon
veto
Sn, Nd, Cd, Se, Gd
orano-metal
metal loaded LSC
1ton -10ton
<= low background
<= energy resolution?
<= Enrichment(?)
Is it possible to
compete with others?

28. 0-,2- b+b+, b+/EC experiments
2n EC/b+ , b+b+ experiment ; No observation year
crystals
shielding
EC/b+ , b+b+
511keV g
New
New method: Active method
EC/b+,b+b+ crystal+ 4p shielding
crystals :
High efficiency,
3 signal coincidence,
Discrimination of 0- and 2- process,
Moderate energy resolution
Typical method with HPGE:
Passive method
Good energy resolution,
Low efficiency (<5%),
No discrimination between
0- and 2- EC/b+ , b+b+

29. List of candidates Nuclide Decay channel Qββ, keV Natural abundance
Decay mode
Half-life
(yr)
50Cr
Εβ+
1171
4.345
0v+2v
1.8*1017
58Ni
Εβ+,2E
1925
68.07
7*1020
4.0*1019
84Sr
1786.8
0.56 0v
7.3*1013
96Ru
2β+,Eβ+
2719
5.54
3.1*1016
6.7*1016
106Cd
2β+, Eβ+
2771
1.25
2.4*1020
3.7*1020
112Sn
1922
0.97
6.1*1013
124Xe
2β+,kβ+
2865
0.09
4.2*1017
1.2*1018
136Ce
2400
0.185
6.9*1017
3.8*1016
78Kr
2866
0.35
2*1021
5.1*1021
92Mo
1649
14.84
1.9*1020
3.0*1018

30. 0,2n EC+b+ , b+b+ Experiment at Y2L
2n EC+b+ , b+b+ ; No observation yet
Interest : 1) Sr-84 : SrCl (7x1013 yr)
2) Ce-136 : CeBr3, Cs2LiCeCl6 (4x1016 yr)
3) Mo-92 : CaMoO4 (2x1020 yr)
4) Cd-106 : CdWO4 (4x1020 yr)
5) Ba-130 : BaF2 (4x1021 yr)
CsI(Tl) 6cm
Low background Pb (10cm)
EC+b+ , b+b+
Crystal
511keV g

31. b+/EC setup with 4p CsI crystals at Y2L

32. Crystal Growing system at KNU
2 Czochalski system
2 Bridgeman system
Crystals for DB
SrCl2
CeBr3
Cs2LiCeCl6
etc

33. Thank you Even if our major goal is CaMoO4 based 100Mo 0-n bb,
still many small scale double beta decay experiment can be performed with existing facility and small budget , and we demonstrated some of that.
Thank you

34. CaMoO4 & SrCl2 : 0n EC/b+ search
Search near 628 keV
Very Preliminary limit: 3x1019 y
84Sr
Search near 765 keV
Very Preliminary limit: 1x1017 y
Grown at KNU

35. 136Ce->136Ba b+b+, b+/EC, ECEC Excited

36. U238
a-a
a-b

37. Th232
a-a
a-a
a-a,a-b

38. CaMoO4 based 100Mo 0-n bb
Ca(x)MoO4 scintillation crystal for 0-n bb search
-> Active source technique
(first presented at new view in particle physics in 2004)
Difference from other 100Mo experiment
Energy resolution 5% (3.03 MeV)
Avalanche photodiode ( 4 times Q.E.)
Detection efficiency : ~ 100%
Pulse shape discrimination : 238U, 232Th background removal
First developed 2003
(5x5x5mm3)