1. Study of Muon-induced Neutrons in the KIMS Experiment
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
Energy [Mev]
PID [MeV/MeV]

7. 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

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 60 GeV muon All events Coincident events with 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
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
IGEX
0.4 cnt/day/liter
EDELWEISS
Boulby f(A)
0.7 cnt/day/liter
Bergamasco
1 cnt/day/liter
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 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