Study of Muon-induced Neutrons in the KIMS Experiment

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Study of Muon-induced Neutrons in the KIMS
Experiment

• 2005. 4. 22.
• The Korean Physical Society
• J.H. Choi

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

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Detector
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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
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PSD of gamma and neutron by neutron detector
Gamma
Neutron
Energy Mev
PID MeV/MeV
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Neutron Problem

• 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

IGEX
500 MeV neutrons
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Time Coincidence

• We expected that we can find the coincidence of
  neutron and muon detector
• We computed the time difference ?t between muon
  and neutron detectors signal
• ?t Min(Muon trigger time Neutron trigger
  time)
• Under a micro second, the coincidence is
  extimated.

coincidence
?t sec
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Coincidence Events
All events
Coincident events with muon
60 GeV muon
Energy MeV
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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 ( gt 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

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Energy spectrum in neutron band

• 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

Events of neutron energy region
The result of simulations with 35cm Pb shielding in other labs The result of simulations with 35cm Pb shielding in other labs
IGEX 0.4 cnt/day/liter
EDELWEISS 0.4 cnt/day/liter
Boulby f(A) 0.7 cnt/day/liter
Bergamasco 1 cnt/day/liter
Coincident events of neutron energy region
Energy Mev
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Summary

• Total Coincidence events 12 cnt/day/liter
• High energy (gt3MeV) 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