1. Jung il LEE for KIMS collaboration Sejong University
A measurement of nuclear recoil with Am-Be neutron source in CsI(Tl) crystal
Jung il LEE for KIMS collaboration
Sejong University

2. Motivation 암흑물질 탐색 실험을 위한 핵 되튐측정. Previous measurement with
mono-energetic neutron beam in accelerator.
WIMP-nucleus recoil study with neutron-nucleus recoil.
Studies on Pulse Shape Discrimination (PSD).
중성자 소스(Am-Be)를 이용하여 지속적이고, 체계적인 연구 가능.

3. Previous test with neutron beam at KIGAM
Results of pulse shape discrimination
6keV< E <7keV
E=2.62MeV

4. KIMS Am-Be neutron source의 특성
9Be(α,n)12C : 수 MeV neutrons
α + 9Be -> 12C*(12C)+ n
12C + γ(4.4MeV)
300 mCi Am-Be source 재활용 (NETEC)
 1.1 x 1010 Bq
 total 7 x 105n/sec 예상 (70 neutrons/106 alphas)
 수백 neutrons/sec hit 3cmX3cm crystal
 limited by slow decay time of CsI(Tl)
We can use it to study recoil signal systematically.

5. Experimental setup at SNU
Source + 20cm Liquid Scintillation Counter (LSC)
5cm Pb shielding
10cm Borated Paraffin
2cm Fe shielding and structure
46o
CsI
BC501a
34cm
37cm
29cm n
LSC
Am-Be
90o
17.4o

6. Electronics diagram detector2 CsI down detector1 detector3 up
Linear fan
In/out
Pre
AMP
Oct.DFD
CF8000
Oct.CFD
DF8000
D.G.G
Dicrimi
nator
Oct. CFD
trigger or
Osc.ext
Adc.partial
Adc.full
LSC
Oct CFD
DGG
Tdc.stop
Adc.gate
Tdc.start
Osc ch1
Osc ch2
Adc
Dlming

7. (Am-Be neutron source) BC501A from source
Gamma
gamma
neutron
Partial charge
Full charge

8. Timing spectra : T(BC501A) – T(LSC)
gamma n

9. 60Co calibration spectrum
60Co timing
Am-Be timing n
gamma

10. Neutron energy spectrum of Am-Be source

11. Calculation of neutron energy spectrum
Lower than the total energy spectrum due to 4.4 MeV
gamma coincidence requirement
counts
En (MeV)

12. Calculation of Nuclear recoil
10MeV
5MeV θ E0 ER m M
1MeV 17 46 90

13. Neutron & gamma separation
Preliminary data with low statistics with only 17 degree Neutron Detector
PID
neutron
Bc501a
gamma
Timing(BC501a-LSC)
PID=(partial charge-55)/fullcharge

14. Pulse shape discrimination of CsI(Tl)
137Cs source Compton signals
Am-Be neutron source signals
Results :
137Cs mean=
Sigma=0.5
Neutron (recoil) mean=
Sigma=0.675
Neutron Recoil signal is shorter
than gamma signal !!

15. 137Cs gamma-recoil Discrimination
2~6keV
6~10keV
10~14keV

16. Conclusion & future
Demonstrated using Am-Be soure to study recoil with 4.4 MeV gamma tagging.
The pulse shape discrimination is shown for nuclear recoil events with short decay time.
Plan 1: increase # of neutron detector (~ 10)
Plan 2 : measure En accurately from Am-Be
Plan 3 : measure the quenching factor of CsI(Tl).
Plan 4 : Use the setup for general recoil measurements

19. Gamma-recoil discrimination
E(keV)

20. Cs137 gamma-recoil discrimination
E(keV)

21. 60Co source data 2 gamma coincidence
T(BC501A) – T(LSC)
60Co
Full vs partial graph
Sigma=1.95ns
Quenching Factor
(=Emeas / Erecoil)를 측정하기
위하여는 약 1 ns 의
Resolution 필요

22. Gamma-recoil discrimination

23. Neutron energy spectrum of 239Pu/Be source

24. Pulse shape discrimination of CsI(Tl)
Cs137 mean=
Sigma=0.5
Neutron (recoil) mean=
Sigma=0.675
Gamma=
sigma=0.525