1. Double Beta Decay Experiment with CaMoO4 crystal
Sejong University
WoonGu Kang
W.G. Kang, Y.D. Kim, J.I. Lee
S.K. Kim1, H. C. Bhang1, S. S. Myung1, S.C.Kim1, J. H. Choi,1 J. H. Lee1, S. Ryu1, S. J. Lee1
H.J. Kim2, J. H. So2,
I.S. Hahn3, M.J Hwang 4, Y.J Kwon 4
KIMS Collaboration
I will talk about double beta decay experiment with CaMoO4 crystal at LN2 temperature
Department of Physics, Sejong University, South Korea  
1Department of Physics and Astronomy, Seoul National University, South Korea  
2Department of Physics, Kyungpook National University, South Korea. 
 3Department of Science Education, Ewha Woman’s University, South Korea.  
4Institute of Physics and Applied Physics, Yonsei University, South Korea

2. 0ν double-beta decay (0νββ)
e- or e+
e- or e+ ▲ W W W
(A,Z+2)+2e-
(A,Z -2)+2e+
NUCLEAR
PROCESS
(A,Z)
2n → 2p + 2e-
2p → 2n + 2e+
If neutrino is a massive Majorana particle,the neutrino mass can be measured with 0neutrion DBD experiment
The 0-neutrino double beta decay which two neutrons inside a nucleus spontaneously transform into two
protons and no involves neutrino.
The two electron must be emitted because charge conserve but the total lepton number is not conserved by
two units
The 0-neutrino double beta decay rate is proportional to an effective neutrino mass term
In the result, neutrino absolute mass cab be studied by 0-neutrino double beta decay
0ν2β decay rate ∝ effective mββ term
Neutrino absolute mass can be studied by 0νββ decay
48Ca, 76Ge, 82Se, 100Mo, 92Mo ,116Cd, 130Te, 136Xe, 150Nd

3. Decay Mode Of 100Mo and 92Mo ■ β+/EC Q-value=0.628 MeV
Fig1. Energy level scheme of 2β- decay
Fig2. Energy level scheme of EC/β+ decay
■ 2β- Q-value=3.043 MeV
■ β+/EC Q-value=0.628 MeV
The DBD can be generate in the case, the single beta decay of parent nucleus is strongly suppressed because energy conservation.
We have performed a EC/b+ and 2b- decay experiment using a CaMoO4 crystal
In case of 2beta- and EC/beta+ decay, Q-value is 3.043MeV and 0.628MeV for each Mo100 and Mo92
100Mo -> 100Ru + 2e MeV(Q-value)
92Mo + e+ -> 92Zr + e MeV(Q-value)

4. Yangyang Underground Laboratory
(Upper Dam)
(Power Plant)
Korea Middleland Power Co.
Yangyang Pumped Storage Power Plant
(Lower Dam)
Our lab is located at 700m deep under Mt.JeomBong(~1400m high)
Y2L is established by KIMS(Korean Invisible Matter Search) group for WIMP search

5. Test Setup of CaMoO4 at LN2 Temperature
Vacuum Chamber with He Cryostat can lower the temperature of
crystal down to 70K.
CaMoO4 crystal(18mmX18mmX14mm) wrapped with Teflon sheet.
1inch PMT
This is test setup for DBD experiment with CaMoO4 crystal at liquid N temperature in sejong University

6. Temperature Dependence of Scintillation Properties of CaMoO4 Crystal
The measured dependence of relative light output of CaMoO4 Crystal on the temperature is present in figure.
The temperature decreases down to -80 degree, the light yield increases by a factor of 2.5
Mikhrin et al.
Annenkov et al.
Light yield of LN2 temp  increases ~ 3 times of Room tem.

7. Decay Time @ Low Temperature
Pulse shape
Time (ns)
Decay time of temperature dependence
(see Fig.)
As the temperature is lowered
the scintillation decay time constants increase very rapidly at first

8. Test at Sejong Univ. Single photoelectron spectrum @ Room temperature
750V, X50 Amp.
FWHM = 11.62±1.42 % ( -150 ℃)
Number of photoelectron distribution.
Due to long decay time, many events are ovelapped in 300 micro second time duration.
1.13 photoelectrons/keV
crystal with low light yield.
HV not optimized at low temp.
Time range can be optimized.
662 keV peak
Overlapped events

9. Quantum Efficiency of Photocathodes-I
I did compare with quantum efficiency for each of pmt photocathodes
This is figure for quantum efficiency curve
In figure, the ss25 photocathodes with maximum quantum efficiency at 552nm
UBA(Ultra-bialkali), SBA(Super-bialkali), RbCs(KIMS PMT), SS25(multibialkali)

10. Quantum Efficiency of Photocathodes-II
RbCs
8.67±0.04
SBA
8.32±0.09
5.37±0.79
6.76±1.18
Bialkali
8.73±0.09
7.07±0.71
SS25
8.80±0.13
This is # of p.e spectrum of 662keV gamma-ray from Cs137 source measured with the 1x1x1cm CsI(Tl) crystal
Before, the get spectrum ..I tried to match the gain for each pmt
(So, Left figure is # of p.e spectrum of each PMT at room temperature)
In p.e spectrum, the # of p.e with the three group of ss25 , sba and rbcs photocathodes are similar in size
But, # of p.e of RbCs more than the ss25 and sba
7.25±1.10
# of p.e Spectrum of each PMT at Gain Matching
PMT Gain Matching

11. PLAN ■ We will test new APDs(Silicon Avalanche Photodiodes)
->The APDs is produce by Radiation Monitoring Devices, Inc)
■ We confirmed good energy resolution of CaMoO4 crystal + APDs
detector at LN2 temperature