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 pas

s through an underground in de

pth.

• Neutrons can be generated by t

he muon when the muon throug

h out material

• The everage energy of muons i

s 216 GeV at 2500 mwe in IGE

X lab.

• The flux of cosmic muon is 4.3x

10-7 cnt/cm2/s at 2000 mwe in K

IMS lab.

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Detector

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• CsI(Tl) crystal is shielded by 30c

m mineral oil, 15cm lead, 5cm PE,

10cm Cu

• All of other detectors are surround

ed by the muon detectors

• Neutron detector is located inside

PE and outside Cu

• CsI crystal detector is in the copp

er box.

Detector

CsI(Tl) Crystal

Muon Detector

Neutron Detector

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PSD of gamma and neutron by neutron detector

Energy [Mev]

PID [MeV/MeV]

Gamma Neutron

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Neutron Problem• Neutron signal is identical to the WI

MP signal in CsI(Tl) crystal• Neutrons can generated by a variety

of process• For example, muon-induced neutron

s 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

IGEX

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• We expected that we can find the

coincidence of neutron and muon

detector

• We computed the time difference

Δt between muon and neutron det

ector’s signal

• Δt = Min(Muon trigger time – Neut

ron trigger time)

• Under a micro second, the coincid

ence is extimated.

Time Coincidence

coincidence

Δt [sec]

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Energy [MeV]

All events

Coincident events with muon

Coincidence Events

60 GeV muon

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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 ( > 3Mev) in neutron detector are almost from c

osmic 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-induce

d neutrons are found• 0.025 cnt/day/liter• The size of data is too small• The way for shielding(15cm P

b + 5cm PE) is different from simulations of other labs

Energy [Mev]

Coincident events of neutron energy region

Events of neutron energy region

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

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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 muo

n 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