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Study of Muon-induced Neutrons in the KIMS Experiment

Study of Muon-induced Neutrons in the KIMS Experiment. 2005. 4. 22. The Korean Physical Society J.H. Choi. Underground Laboratory. Yangyang KIMS Lab. Depth : 700m 2000m(mwe). Underground Laboratory. The high energy muon can pass through an underground in depth.

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Study of Muon-induced Neutrons in the KIMS Experiment

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  1. Study of Muon-induced Neutrons in the KIMS Experiment 2005. 4. 22. The Korean Physical Society J.H. Choi

  2. Underground Laboratory Yangyang KIMS Lab. Depth : 700m 2000m(mwe)

  3. Underground Laboratory • The high energy muon can pass through an underground in depth. • Neutrons can be generated by the muon when the muon through out material • The everage energy of muons is 216 GeV at 2500 mwe in IGEX lab. • The flux of cosmic muon is 4.3x10-7 cnt/cm2/s at 2000 mwe in KIMS lab.

  4. Detector

  5. Detector • CsI(Tl) crystal is shielded by 30cm mineral oil, 15cm lead, 5cm PE, 10cm Cu • All of other detectors are surrounded by the muon detectors • Neutron detector is located inside PE and outside Cu • CsI crystal detector is in the copper box. Muon Detector Neutron Detector CsI(Tl) Crystal

  6. PSD of gamma and neutron by neutron detector Gamma Neutron Energy [Mev] PID [MeV/MeV]

  7. Neutron Problem IGEX • Neutron signal is identical to the WIMP signal in CsI(Tl) crystal • Neutrons can generated by a variety of process • For example, muon-induced neutrons in the Pb shielding, muon-induced neutrons in the rock, neutrons from radioactivities in the rock, neutrons from radioactivities int the air and so forth • Most of the neutrons are easily vetoed because of their low energy compared with moun induced neutrons in the shieldings • We want to avoid neutrons induced by muons in the shieldings 500 MeV neutrons

  8. Time Coincidence • We expected that we can find the coincidence of neutron and muon detector • We computed the time difference Δt between muon and neutron detector’s signal • Δt = Min(Muon trigger time – Neutron trigger time) • Under a micro second, the coincidence is extimated. coincidence Δt [sec]

  9. Coincidence Events All events Coincident events with muon 60 GeV muon Energy [MeV]

  10. Coincidence Events • Events of total energy contain neutron events, gamma events, muon events and so forth. • The total coincident events’ rate is 12 cnt/day/liter. • High energy events ( > 3Mev) in neutron detector are almost from cosmic muon. • Coincidence events rate in high energy region is 4 cnt/day/liter. • 6x10-5 cnt/sec • Muon Flux : 4.3x10-7 cnt/cm2/s • 3x10-5 cnt/sec • Most of the low energy events are gamma events induced by cosmic muon

  11. Energy spectrum in neutron band Events of neutron energy region • 2 candidates of muon-induced neutrons are found • 0.025 cnt/day/liter • The size of data is too small • The way for shielding(15cm Pb + 5cm PE) is different from simulations of other labs Coincident events of neutron energy region Energy [Mev]

  12. Summary • Total Coincidence events 12 cnt/day/liter • High energy (>3MeV) coincidence events 4 cnt/day/liter • Neutron band coincidence events 0.025 cnt/day/liter • We are studing of the coincident time information of the muon detector and the CsI detector • We are making a study of the simulation with GEANT4 and FLUKA to find a rate of neutrons induced by muons

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