Coincident Neutron Flux

Report
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)
2005-04-22
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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.
2005-04-22
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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
Muon Detector
surrounded by the muon detectors
• Neutron detector is located inside
Neutron Detector
PE and outside Cu
• CsI crystal detector is in the
copper box.
2005-04-22
CsI(Tl) Crystal
5
PSD of gamma and neutron by neutron detector
Energy [Mev]
Gamma
Neutron
PID [MeV/MeV]
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Neutron Problem
IGEX
500 MeV neutrons
2005-04-22
• 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, muoninduced 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
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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
•
coincidence
Δt = Min(Muon trigger time –
Neutron trigger time)
•
Under a micro second, the
coincidence is extimated.
Δt [sec]
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Coincidence Events
All events
Coincident events with muon
Energy [MeV]
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60 GeV muon
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
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Energy spectrum in neutron band
• 2 candidates of muoninduced 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
Coincident events of
neutron energy region
Energy [Mev]
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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
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
2005-04-22
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