Recent status of dark matter search with ULE-HPGe detector Tsinghua University Qian Yue 2007.11.23 2...
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Transcript of Recent status of dark matter search with ULE-HPGe detector Tsinghua University Qian Yue 2007.11.23 2...
Recent status of dark matter search with ULE-HPGe detector
Tsinghua University
Qian Yue
2007.11.23
2nd Korea-China Joint Seminar on Dark Matter
Search
Contents :
1. Physics goal
2. Detector system
3. The first physics result
4. Neutron background Study
5. QF measurement preparation
The recent results and our goal region
Our detector systemOur detector system 5g Ge prototype detector5g Ge prototype detector
Detector @ Y2L detector simulation Detector @ Y2L detector simulation
Y2L environment parameter
1~2 pCi/liter空气中 222Rn含量
8×10-7/cm2·sμ子通量
2.7×10-7/cm2·s中子通量
74m2×5m内部空间
4.1%K2O
5.6±2.6 ppm232Th
< 0.5 ppm238U岩石成分
35 ~ 60%湿度
20 ~ 25℃温度
2 km入口通道长度
~700 m最小岩石厚度
Y2L实验室名称
Setup and DAQ system
HPGe High Gain (0~9keV)
HPGe Low Gain (0~100keV)
CsI(Tl) anti-Compton detector
(Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray)
2
113.13
12.9617
offset eV
ndf
HPGe High Gain (0~9keV) HPGe Low Gain (0~100keV)
(Np, Ag ( X-ray), Am (gamma))
2
0.0694
20.67
offset keV
ndf
HPGe detector calibration
i ii
ii
I tt
IPSD:
CsI(Tl) energy threshold ~ 10keV
( ) 131.419
( ) 160.646
ns
n ns
Veto condition
CsI(Tl) signalTime relation between
CsI(Tl) and HPGe signals
Blue : γ eventGreen: n eventRed: Bg
Energy Threshold: 300eV
Event rate @ threshold
~103cpd
Energy range : 300eV ~ 100keV
Veto efficiency : 60%
Mean background rate :~ 40 cpd
Threshold Background Event Rate
max
min ( )
( , ) ( ) ( )R
vT
W W RR Rv E
NdR df m vf v vE dv
dE m dE
Physical result
0 2 ( ) (for coherent cross-section)c RR c
dF E
dE
2max 2
20 0
min
10
0 0
2
0 1( ) ( ) ( )
escR
RRc v vc E
E r vT R T
v
kdRdRm E rmdE kdE
N vf v F E dv N v c e e
0 2
2 2c n
W nA
r
A r
max
2 21
1 1
( ) ( , )
k
k km E m
Parameter :Eth : 300eVBG rate @ Eth : 900cpdEnergy : 300eV~10keVm×T : 0.7kg•day
2 30.3GeV c cm
0 230 /v km s
232 /sunv km s
650 /escv km s
Physical result
What should be considered?What should be considered? Background level is still high than Background level is still high than
expected.expected.
What’s the source of background?What’s the source of background?
Veto efficiency improve?Veto efficiency improve?
Energy range : (300eV) ~ 100keV (1keV/bin)
Possible main Background source: neutron
Veto efficiency of CsI detector
Red : BgBlue : γGreen: n
Neutron flux and spectrumNeutron Spectrum in CPL was used for neutron simulation
Neutron flux in Y2L: 8 x 10-7 /cm2/s (1.5MeV < En < 6MeV)
Neutron simulationN = 1E6 After Veto
Shielding EfficiencyShielding Efficiency
N=1E6 , Ge range: 0~100 keV:N=1E6 , Ge range: 0~100 keV: 216(130) events before(after) veto216(130) events before(after) veto
Flux: Flux: 8 x 10-7 /cm8 x 10-7 /cm22/s/s Area: 90*60*4 + 60*60*2 cmArea: 90*60*4 + 60*60*2 cm22
Event rate in Ge:Event rate in Ge: 0.43(0.26) counts/day0.43(0.26) counts/day 0.86(0.52) counts/(day*Kg*keV)0.86(0.52) counts/(day*Kg*keV) CsI Veto Eff. : 40%CsI Veto Eff. : 40%
New detector for neutron background measurement: 1. fast neutron 2. thermal neutron 3. reject low energy gamma background 4. physical match the room of Ge detector
Detector selection :
1,Stilbene to measure fast neutron and reject gamma background based on PSD
2, BC702 scintillation counter to measure thermal neutron
Neutron background measurement
Physical Properties of Stilbene(C14H12)
• Molecular weight (g/mol) 180• Density (g/cm3) 1.22• H/C - ratio 0.857 • Melting point (°C) 124 • Wavelength of emission (nm) 390 • Refractive index 1.64 • Light output : 1.4 ×104 photons/MeV• Decay time (3.5ns ) • Energy resolution <10%, (137Cs conversion electrons)• Radiation degradation (Mrad) 4.0 • Working temperature -40 to 60°C • Quench factor 0.1-0.2 ?• Two components 3ns fast & 400ns slow
Energy resolution
~160KeV for 2.5Mev n
Neutron Gamma Identification
stilbene volume: 4cm * 4cmFADC: 12bit; 200 MHz; dtF =25 ns ; dts =125ns AmBe (americium-beryllium) r and n source
Energy range of n / identification
Energy range for n/r identification: Ee= 100KeV Neutron energy is 0.5 MeV - 1.0MeV
AmBe (americium-beryllium) Source spectrum
Merit of stilbene with energy & sampling (M= 1 , Ee/ = 100KeV in 12bit)
200Mhz Samples
M=deltaP/(W+Wn)
BC 702 thermal neutron detector
Light out : Comparable to NaI(Tl)Light out : Comparable to NaI(Tl) Decay time : 0.2 Decay time : 0.2 ss Wavelength : 450nmWavelength : 450nm High efficiency for detect neutronHigh efficiency for detect neutron
Against gamma Against gamma
Neutron energy efficiency 0.01eV 60% 0.025eV 55% 0.1eV 30% 1eV 10%
Ge detector structureGe detector structure
BC702 Light out : Comparable to NaI(Tl) Decay time : 0.2 s Wavelength : 450nm Neutron energy efficiency 0.01eV 60% 0.025eV 55% 0.1eV 30%
Neutron DetectorNeutron Detector
Base
200
BC702
PMTR6233
50
6.4
43
100
?
Stilbene
OFHC copper 2mm
Cable
2510
•Stilbene•Refractive index 1.64•Light output (104 photons/MeV) 1.4•Decay time (ns) 3.5 •Wavelength 390 nm
PMT R62333” K free
Parameters of detector
PMT : efficiency and rise time better than RCA 8575
FADC : 200MHz and 12bit Cable : shorter and 50 ohm
BC701/stilbene arrangement ( different light reflector design & light collection) Double crystal detector performance ?
Neutron energy recoil proton energy quench factor ?
Energy range of n /r identification ? Detection efficiency of neutron ?
Our setup for simulation(Contributed by Prof. Chunxu Yu @ nankai university)
Detector: Stilbene, Source: neutron, Source position: center of the tubeTube size: h = 5 cm, d = 5cm
Monte Carlo study:Number of recoil protonMonte Carlo study:Number of recoil proton
Monte Carlo study:Energy of recoil protonMonte Carlo study:Energy of recoil proton
Energy deposited in crystal Energy deposited in crystal random & centralrandom & central
1, The detector will be ready in Dec.
2, We need to study the detector using source in Beijing
3, The detector will be sent to measure neutron background at Y2L.
Things to do for neutron BG measurement:
QF measurement for ULE-HPGe QF measurement for ULE-HPGe Experimental setupExperimental setup
The minimum neutron energy can reach down to about 30 keV, but the neutron energy spread is large near the threshold. For example, 1 keV target thickness can lead to ~ 20 keV energy spread for the neutrons. So, it is better to choose higher neutron energy to reduce the neutron energy spread.
SummarySummary
ULE-HPGe RUN Period I have ULE-HPGe RUN Period I have finished: ~40cpd,veto efficiency finished: ~40cpd,veto efficiency 60%60%
Background source should be Background source should be studied: neutron or otherstudied: neutron or other
New detector for neutron BG New detector for neutron BG measurement under constructionmeasurement under construction
QF measurement of ULE-HPGe QF measurement of ULE-HPGe Detector upgrade to 4*5g ArrayDetector upgrade to 4*5g Array