Transcript Coincident Neutron Flux

The Study of Muoninduced Neutrons in The
KIMS Experiment
2005. 10. 22.
The Korean Physical Society
J.H. Choi
Underground Laboratory
Yangyang KIMS Lab.
Depth : 700m
2000m(mwe)
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Muon Spectrum in Laboratory
•
The high energy muon can
pass through an underground
in depth.
KIMS
•
Neutrons can be generated by
the muon when the muon
through out material – mimic
WIMP
Geant4 Simulation
•
The everage energy of muons
dN / dE
is 216 GeV at 2500 mwe in
IGEX lab.
•
The flux of cosmic muon is
2.7x10-3 cnt/m-2s-1 at 2000 mwe
in KIMS lab.
P.Lipari et al., Phys.Rev.D44(1991)3543
Energy [MeV]
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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.
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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
• Δt = Min(Muon trigger time –
Neutron trigger time)
• The pick shows the information of
coincidence
Δt [sec]
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Muon-induced Neutron
Experiment Result
Neutron
0.025 cnt/day/liter
Energy [Mev]
Gamma
Events of neutron energy region
Coincident events of
neutron energy region
Energy [MeV]
PID [MeV/MeV]
• 2 candidates of muon-induced neutrons are found
• The size of data is too small
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Geant4 Simulation
Length [cm]
Theta Angle [degree]
Energy [MeV]
•
Phi Angle [degree]
Total 282,000 muons are fired with angle distributions.
- 170.8 days(MC) / 67.4 days(Exp)
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Generated Neutrons in Detector
Total
Length [cm]
Lead
Energy [MeV]
Length [cm]
•
Most of neutrons are generated in the lead.
- 2.45 x 10-10 cnt/cm-3s-1
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Generated Neutrons – 1cm and 35cm
Total
Secondary
1.46x10-4 /muon/(g/cm2)
16 %
Primary
84 %
By Geant4
IGEX : 8.8x10-5 /u/(g/cm2)
By Fluka Simulation
Energy [MeV]
Energy [MeV]
78 %
4.6x10-4 /u/(g/cm2)
Energy [MeV]
22 %
By Geant4
IGEX : 1.7x10-3 /u/(g/cm2)
Energy [MeV]
By Fluka Simulation
•
•
Energy [MeV]
Energy [MeV]
The rate of neutron production of Fluka is at most 2 times more than Geant4 over
100GeV.
The rate of neutron production of Geant4 depend on physics model at least 2
times.
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Deposited Coincedence Energy - MC
•
The coincidence events rate
with muon detector is 38.94
0 ~ 150MeV
evt/day under 150 MeV
•
ToTal : 38.94 evt/day
Muon :
4.32 evt/day
The coincidence events rate
with muon detector is 8.30
E.M. : 34.62 evt/day
evt/day over 2.5 MeV
•
In the high energy, most of
evnets are from muon
•
In the low energy, most events
are from E.M.
•
Neutron is not detected in the
170.8 days MC simulation data
– We need more statistics
– We need study of MC model
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dependence
Coincedence Energy – Exp.
•
The coincidence events rate
with muon detector is 14.64
2.5 MeV ~
evt/day from 150KeV to 10
Exp. : 5.21 evt/day
MeV
•
M.C. : 8.30 evt/day
The coincidence events rate
with muon detector is 5.21
evt/day over 2.5 MeV
•
In the 67.4 days data, two
candidate events of muon-
induced neutrons are
detected
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Coincidence Low Energy
•
150KeV~2.5MeV
MC
16.31 evt/day
Exp.
9.36 evt/day
The coincidence events rate
with muon detector is 16.31
evt/day from 150KeV to 2.5
MeV in M.C.
•
The coincidence events rate
with muon detector is 9.36
evt/day from 150KeV to 2.5
MeV in Exp.
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Summary & Plan
•
The flux of cosmic muon at 2000 mwe in KIMS lab is 2.7x10-7 cnt/cm-2s-1
•
The rate of generated neutrons by Geant4 MC simulation is 2.45 x 10-10
cnt/cm-3s-1 in lead of KIMS detector.
•
The rate of generated neutrons in 35cm Pb
4.6x10-4 /muon/(g/cm2) (KIMS-Geant4) : 1.7x10-3 /muon/(g/cm2) (IGEXFluka)
•
Total Coincidence events (150KeV~2.5MeV)
9.36 evt/day(Exp.) : 16.31 evt/day(M.C.)
•
2 candidates of muon-induced neutrons are found in KIMS Experiment
•
We need more statistics for M.C.
•
These result will be also tested with adequate physical model of Geant4
•
We are studying the coincidence between the muon detector and the CsI
detector
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