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

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

Detector 2005-04-22

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 2005-04-22

PSD of gamma and neutron by neutron detector Energy [Mev] PID [MeV/MeV] 2005-04-22

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 2005-04-22

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] 2005-04-22

Coincidence Events 60 GeV muon All events Coincident events with muon Energy [MeV] 2005-04-22

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 2005-04-22

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] 2005-04-22

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