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Status of ULE-HPGe Experiment for WIMP Search in YangYang

Status of ULE-HPGe Experiment for WIMP Search in YangYang. Li Jin. July 2006. 5g Ge. 1cpd. Motivation. Current weapon: 5g prototype Ge detector 16.94kg CsI(Tl) veto detector. Expected threshold: ~100eV. Target. Current System Setup. ULE - HPGe detector. FADC & VME crate.

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Status of ULE-HPGe Experiment for WIMP Search in YangYang

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  1. Status of ULE-HPGe Experiment for WIMP Search in YangYang Li Jin July 2006

  2. 5g Ge 1cpd Motivation Current weapon: 5g prototype Ge detector 16.94kg CsI(Tl) veto detector Expected threshold: ~100eV Target

  3. Current System Setup ULE - HPGe detector FADC & VME crate H.V. (CEAN 1527) Amp. (CANBERRA 2026) HPGe: -500V CsI(Tl): -1300V Shaping time: 6us Gain: ×20

  4. System Schematic Diagram Typical signals: HPGe High gain (0~9keV) HPGe Low gain (0~100keV) CsI(Tl) channel (current signal)

  5. HPGe Calibration – high gain channel Peaks: Ta, Ca, Cs, Ti, Mn, Fe, Cu X-ray After gain correction and pedestal shift correction

  6. HPGe Calibration – low gain channel Peaks: Np (L X-ray), Ag (K X-ray), Am (alpha decay gamma)

  7. CsI Calibration Gamma energy: Cd-109 (Ag X-ray): 22.577 keV Am-241: 59.5412 keV U-238 (Th-234): 92.6 keV Co-57: 123.66 keV

  8. CsI noise reduction Time coincidence between HPGe and CsI PSD parameter: Threshold ~ 10keV Veto condition Red: background file, Green: neutron file, Blue: Gamma file

  9. Background and Threshold Still far from expected…

  10. Background level Energy region: threshold(300eV) ~ 100keV Blue: after veto, Red: before veto Average background level ~ 40 cpd Average veto efficiency ~ 60%

  11. Veto Efficiency Energy region: threshold(300eV) ~ 100keV (1keV/bin) Blue: gamma files, Green: neutron files, Red: background files Main origin of background: neutron

  12. Neutron background study by Monte Carlo Simulation

  13. Energy of Neutron Source Source :The spectrum of neutron in laboratory (same Cf252) Position: top of Pb Shielding

  14. Energy deposited in Ge Detector • Electron and positron energy • Recoil energy of Ge * 0.25

  15. Energy deposited in Ge Detector300eV to 100KeV Most events are below 10KeV and Decrease very fast !

  16. VETO efficiency of Cs Dtector • The threshold is 20KeV • Efficiency is 100% while energy higher 10KeV • Efficiency is lower than 30% when energy below 10KeV

  17. The comparison between simulation and data Simulation results The neutron background mainly Below 5KeV ,consists with data Experimental data

  18. PSD – two shaping time Background spectrum Parameter: PSD efficiency Eth ~ 50eV improvement

  19. Noise level & distribution Noise level ~ 105 eV (FWHM) • Assumptions: • Pedestal events are all generated by electronics, independent of the detector. • Detector mass: 5g  1kg (200 times) Predicted threshold: 230eV (70eV improvement)

  20. Ge Detector characteristic peaks Previous result: 1.3keV, 10.3keV Current result: 0.923keV, 10.08keV Ge characteristic X-ray: K series ~ 10.089keV, L series ~ 1.209keV Cu characteristic X-ray: K series ~ 8.905keV, 8.042keV, L series ~ 0.948keV F characteristic X-ray: K series ~ 0.677keV

  21. Neutron Experiment Relics

  22. Summary • Detector mass: 5 g (Ge) • Background level: 40 cpd • Threshold: 300 eV • Veto-efficiency: 60% • Measured noise level: 107.6 eV (FWHM) • The main origin of background may be the neutron from environment based on the simulation study.

  23. Plan in the future… • Accumulate more background data physics result • Increase the mass of detector(5g 20g) • Internal radiation study & neutron recoil experiment • Monte-Carlo simulation for neutron and gamma background • Neutron shielding

  24. Thanks!

  25. Calibration Energy 1.7KeV • The Ta characteristic X-ray comes from X-ray generator itself. • The generator uses a kind of Pyroelectric crystal, LiTaO3, as the target and accelerate electrons. • When measured spectrum using the X-ray generator there is a 1.7keV energy peak. • Among all the possible materials in experiment devices, the M-series X-ray of Ta is the onlyfound and known material that accordsto the about 1.7keV peak in measured spectrums. • So 1.7eV is assumed to be Ta M-series X-ray and used for calibration.

  26. The electronics fot 20g detectror

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