Status of neutron simulations Piotr Mijakowski (Warsaw) ArDM meeting, 2010/12/03 1

Outline P.Mijakowski 2 ArDM meeting, 3 Dec 2010 Updated results on rock neutron simulation at CANFRANC –run simulation on a computer cluster with Geant –2 tested configurations: (1)with 2 holes in the shield: 30 cm diameter each hole, 50 cm thick shield (2) no holes (50 cm of polyethylene) 50 cm

Energy spectrum of rock neutrons 3 energy spectrum of neutrons at rockface – input for simulation parametr ization M.J. Carson, J.C. Davies et al., Astroparticle Physics 21(2004) P.Mijakowski3  rock ~ 3.8 × n/(s·cm 2 ) CANFRANC (old hall) : J.M. Carmona et al., hep-ex/ ArDM meeting, 3 Dec 2010

P.Mijakowski4 with holesw/o holes generated events 3.7× × 10 9 livetime days ( hours) days ( hours) #events which hit shield ~55k per hour #events which get inside holes in the shield ~237 per hour - #events which get through the shield and hit detector external container evts 35.9 ± 0.2 per hour (860.6 ± 5.7 per day) above 100 keV: 4.1 ± 0.1 per hour 70 evts ± per hour (0.66 ± 0.08 per day) above 100 keV (9 evts): 0.08 ± 0.03 per day #events which get inside active volume (not unique!) 17.7 ± 0.2 per hour (424 ± 4 per day) ± per hour (0.30 ± 0.05 per day) 50 cm thick polyethylene shield with bottom and top lid of 50 cm height two cylindrical holes in the shield of a 30 cm diameter each ArDM meeting, 3 Dec 2010 all errors statistical only these evts are stored in NTUPLE NO SHIELD: 12k evts per hour hit external container WITH SHIELD & NO HOLES: ~ 5 ×10 5 neutron flux container WITH SHIELD & WITH HOLES: ~ 3×10 2 neutron flux container

P.Mijakowski with holes- neutrons at external container m m r =7.3 m z y 40.3 m 29 m z x ArDM meeting, 3 Dec 2010 X y z top lid is flat NTUPLE: parametrs of neutrons stored at the entrance of ArDM external container external container diameter = m

P.Mijakowski no holes- neutrons at external container m m r =7.3 m z y 40.3 m 29 m z x NTUPLE: parametrs of neutrons stored at the entrance of ArDM external container X external container diameter = m ArDM meeting, 3 Dec 2010 z y

P.Mijakowski Neutrons at external container 7 Energy at external container 13% (9 neutrons) above 100 keV ArDM meeting, 3 Dec % neutrons above 100 keV WITH HOLESNO HOLES Would expect for neutrons above 100 keV: 0.08 n/day  ~0.04 n/day (interact)  ~0.02 n/day (multiple scattering) no holes: 4.1 n/hour  ~2 n/hour (interact)  ~1 n/hour (multiple scattering) with holes:

P.Mijakowski Summary & Plan thickness of the shield seems to provide sufficient protection against neutrons from rock radioactivity holes are a bit of a problem 8 Summary: Plan: pass the codes and ntuples to the group (dedicated simulation of neutrons stored at external container – investigate multiple scattering, interactions etc.) ArDM meeting, 3 Dec 2010

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P.MijakowskiArDM meeting, 3 Dec 2010 Rock neutron simulation in Geant4 50 cm thick cylindrical polyethylene shield 10 2 cylindrical transmission holes on side (filled with air) 50 cm Ilustr: 3 MeV neutron coming from the wall Neutrons related to radioactivity in rock simulated on all planes of CANFRANC hall –2m of concrete around the hall is also included (backscattering) 30 cm diameter each Continous energy spectrum of neutronsat rock surface … NEXT SLIDE

P.Mijakowski PREVIOUS - WRONG LIVE-TIME CALCULATION 11ArDM meeting, 29 Oct 2010 with holesw/o holes generated events × × 10 6 livetime [hour] 57 h 1min56 h 22 min #events which hit shield ~12k per hour ~12k per hour #events which get inside holes in the shield 2994 ~52.5 per hour - #events which get through the shield and hit detector external container 448 ~7.9 per hour 0 #events which get inside active volume 190 ~3.3 per hour 0 50 cm thick polyethylene shield with bottom and top lid of 50 cm height two cylindrical holes in the shield of a 30 cm diameter each