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Muon and Neutron detector of KIMS experiment

Muon and Neutron detector of KIMS experiment. Jungwon Kwak and JingJun Zhu DMRC. 2003-09-23. Backgrounds in KIMS experiment. External background Sources Cosmic rays – muon Reduce in Deep underground ( 10 -5 level of ground in 700 m underground )

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Muon and Neutron detector of KIMS experiment

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  1. Muon and Neutron detector of KIMS experiment Jungwon Kwak and JingJun Zhu DMRC 2003-09-23

  2. Backgrounds in KIMS experiment • External background Sources • Cosmic rays – muon • Reduce in Deep underground • ( 10-5 level of ground in 700 m underground ) • Radioactive source in Environmental material – Gamma, Neutron • Lead, Mineral Oil, Copper shield ( mainly related with U238, Th232, K40) • Rn in air – Alpha • N2 flowing • Internal background sources • CSI crystal – Cs137,134 Rb • R&D for ultra low background CSI crystal ( currently 10 cpd level) • PMT background – glass window, noise signal • Quartz window PMT with low background • Main shielding - Stainless steel, lead, copper • Pure copper, low background lead MUD CSI NMD

  3. Diagram of KIMS detector Active Detector CSI Cs(Tl) Crystal Detector MUD NMD Neutron Monitor Detector PE shield (5cm) Pb shield (15cm) MUD Muon Detector - LS 5% Copper shield (10cm) CSI Passive shield NMD Copper : 10 cm PE : 5 cm Lead : 15 cm Mineral Oil : 30 cm Mineral Oil shield (30cm)

  4. NMD Neutron background MUD • To understand neutron background well is important in dark matter search experiment because neutron signals mimic the WIMP signals. • Neutron background source: • cosmic ray induced neutron • spontaneous fission of U238 • (α,n) reaction of U & Th in the rock • Neutron flux at underground laboratory is very small, so we need a large detector and a long term measurement. CSI

  5. NMD Neutron Monitor Detector Liquid Scintillator BC501A 20 liter ( 16 cm diameter x 100 cm ) 10 liter ( 16 cm diameter x 50 cm ) 2 x 5” PMT 10-3 times of Neutron rate inside main shield MUD CSI inside Pb 5 cm shield inside main shield

  6. NMD DCC method MUD 20liter BC501A Neutron Detector DCC(Digital Charge Comparison) method: tail of signal / total signal for BC501A scintillator neutron and gamma signal separation using pulse shape CSI

  7. NMD Neutron background inside main shield

  8. NMD time variation • Fitting function = lifetime (3.8 days for Rn) + constant • Constant flux : 27 counts / day /liter • Data taken just after windows are sealed

  9. NMD FADC DAQ system • 10liter BC501A Neutron Detector used • 1G Hz data sampling using digital oscilloscope • Data taken two month later window sealing Scatter plot of part/full for each PMT Energy spectrum of neutron candidates (MeV) Flux for Neutron candidate = 29 counts / day / liter

  10. MUD MUon Detector/Neutron Shield MUD 7 MUD 1 MUD 4 MUD 6 MUD 8 MUD 2 MUD 3 MUD 5 MUD CSI 2x2” PMT for each channel 8 muon modules , 28 signal channels Liquid Scintillator5 % PC 1 liter + PPO 4 g + POPOP 15 mg Mineral Oil95 % 10-5 times of ground Muon rate at Y2L

  11. MUD Muon detection Efficiency MUD CSI Trigger Muon using two other scintillator detectors in the Ground lab Use one(MUD2) of muon modules

  12. MUD Attenuation length MUD CSI Fitting function : two exponential decay function Fitting results : fast term - 50 cm , slow term – need more length

  13. MUD Muons in Y2L and CPL MUD CSI • Ground level: ~ 8.64x 106muons / day.m2 = Fluxg • CPL(-350m) : ~1.45 x 103 muons /day.m2 = 1.6 x 10-4 Fluxg • Y2L(-700m) : ~2.20 x 102muons /day.m2 = 2.5 x 10-5 Fluxg

  14. MUD Hit position reconstruction MUD CSI • MUD8 module used • Trigger Muon using Plastic scintillator and MUD2 • Divide 64 x 64 cells and calculate c2values for each cell • choose one cell with minimum c2 • Use only ADC information ( in progress for TDC )

  15. Conclusion • NMD (Neutron Monitoring Detector) • Upper limit of Neutron flux ~ 30 counts/day/liter • Few ppt level of U, Th can cause comparable Alpha rate • Need Checking U, Th level of NMD • MUD (Muon Detector) • Muon efficiency ~ 98 % • Muon flux in Y2L ~ 2.5 x 10-5 of ground level • Muon track reconstruction in progress MUD CSI

  16. NMD Neutron background outside main sheild

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