1 / 38

Recent status of dark matter search with ULE-HPGe detector

Recent status of dark matter search with ULE-HPGe detector. Tsinghua University Qian Yue 2007.11.23. 2 nd Korea-China Joint Seminar on Dark Matter Search. Contents ： Physics goal Detector system The first physics result Neutron background Study QF measurement preparation.

omana
Download Presentation

Recent status of dark matter search with ULE-HPGe detector

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. Contents： • Physics goal • Detector system • The first physics result • Neutron background Study • QF measurement preparation

  3. The recent results and our goal region

  4. Our detector system • 5g Ge prototype detector

  5. Detector @ Y2L detector simulation

  6. 实验室名称 Y2L 最小岩石厚度 ~700 m 入口通道长度 2 km 温度 20 ~ 25℃ 湿度 35 ~ 60% 岩石成分 238U < 0.5 ppm 232Th 5.6±2.6 ppm K2O 4.1% 内部空间 74m2×5m 中子通量 2.7×10-7/cm2·s μ子通量 8×10-7/cm2·s 空气中222Rn含量 1~2 pCi/liter Y2L environment parameter

  7. Setup and DAQ system HPGe High Gain (0~9keV) CsI(Tl) anti-Compton detector HPGe Low Gain (0~100keV)

  8. HPGe detector calibration HPGe High Gain (0~9keV) HPGe Low Gain (0~100keV) (Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray) (Np, Ag ( X-ray), Am (gamma))

  9. Time relation between CsI(Tl) and HPGe signals CsI(Tl) signal PSD: CsI(Tl) energy threshold ~ 10keV Blue： γ event Green：n event Red: Bg Veto condition

  10. Background Event Rate Threshold Energy range：300eV ~ 100keV Energy Threshold: 300eV Event rate @ threshold ~103cpd Veto efficiency：60% Mean background rate : ~ 40 cpd

  11. Physical result

  12. Physical result Parameter： Eth：300eV BG rate @ Eth：900cpd Energy ：300eV~10keV m×T：0.7kg•day

  13. What should be considered? • Background level is still high than expected. • What’s the source of background? • Veto efficiency improve?

  14. Veto efficiency of CsI detector Energy range：(300eV) ~ 100keV (1keV/bin) Red： Bg Blue： γ Green：n Possible main Background source: neutron

  15. Neutron flux and spectrum Neutron Spectrum in CPL was used for neutron simulation Neutron flux in Y2L: 8 x 10-7 /cm2/s (1.5MeV < En < 6MeV)

  16. Neutron simulation N = 1E6 After Veto

  17. Shielding Efficiency • N=1E6 , Ge range: 0~100 keV: • 216(130) events before(after) veto • Flux: 8 x 10-7 /cm2/s • Area: 90*60*4 + 60*60*2 cm2 • Event rate in Ge: • 0.43(0.26) counts/day • 0.86(0.52) counts/(day*Kg*keV) • CsI Veto Eff. : 40%

  18. Neutron background measurement • 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

  19. 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

  20. Energy resolution ~160KeV for 2.5Mev n

  21. Neutron Gamma Identification stilbene volume: 4cm *4cm FADC: 12bit; 200 MHz; dtF =25 ns ; dts =125ns AmBe (americium-beryllium)r and n source

  22. Energy range of n / identification AmBe (americium-beryllium) Source spectrum Energy range for n/r identification: Ee= 100KeV Neutron energy is 0.5 MeV - 1.0MeV

  23. Merit of stilbene with energy & sampling(M= 1 , Ee/ = 100KeV in 12bit) 200Mhz Samples M=deltaP/(W+Wn)

  24. BC 702 thermal neutron detector • Light out : Comparable to NaI(Tl) • Decay time : 0.2 ms • Wavelength : 450nm • High efficiency for detect neutron • Against gamma Neutron energy efficiency 0.01eV 60% 0.025eV 55% 0.1eV 30% 1eV 10%

  25. Ge detector structure

  26. Neutron Detector F 84 F76 BC702 6.4 OFHC copper 2mm Stilbene • BC702 • Light out : Comparable to NaI(Tl) • Decay time : 0.2 ms • Wavelength : 450nm • Neutron energy efficiency • 0.01eV 60% • 0.025eV 55% • 0.1eV 30% 50 PMT R6233 3”K free 200 PMT R6233 100 Cable 25 10 Base 43 ? • Stilbene • Refractive index 1.64 • Light output (104 photons/MeV) 1.4 • Decay time (ns) 3.5 • Wavelength 390nm

  27. 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 energyquenchfactor ? • Energy range of n /r identification ? • Detection efficiency of neutron ?

  28. Our setup for simulation(Contributed by Prof. Chunxu Yu @ nankai university) Detector: Stilbene, Source: neutron, Source position: center of the tube Tube size: h = 5 cm, d = 5cm

  29. Monte Carlo study:Number of recoil proton

  30. Monte Carlo study:Energy of recoil proton

  31. Energy deposited in crystal random & central

  32. Things to do for neutron BG measurement: 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.

  33. QF measurement for ULE-HPGe Experimental setup

  34. 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.

  35. Summary • ULE-HPGe RUN Period I have finished: ~40cpd,veto efficiency 60% • Background source should be studied: neutron or other • New detector for neutron BG measurement under construction • QF measurement of ULE-HPGe • Detector upgrade to 4*5g Array

More Related