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Neutron Shielding

Neutron Shielding. Harry Nelson CDMS EAB August 5, 2004. Neutron Rates (at Soudan). About 20 times smaller than current beta rates… About 2.5 per 1000 kg-d `New Technology’ detector… 20 kg, 300 days, about 6000 kg-d About 15 neutron events…

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Neutron Shielding

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  1. Neutron Shielding Harry Nelson CDMS EAB August 5, 2004

  2. Neutron Rates (at Soudan) • About 20 times smaller than current beta rates… • About 2.5 per 1000 kg-d • `New Technology’ detector… 20 kg, 300 days, about 6000 kg-d • About 15 neutron events… • 1 order suppression would be welcome (>2 orders by move to SNOlab)

  3. The Neutron Background… • Neutrons with 1 MeV energy at the ZIP detectors can fake WIMPs • Hydrogen (in polyethylene) shields very well • High energy neutrons (>50 MeV) can penetrate deep into the shield, and make secondary 1 MeV neutrons that never experienced shielding; these 1 MeV neutrons can fake WIMPs

  4. m 1 MeV neutron 100 MeV neutron ZIP Lead Polyethylene Scintillator Rock

  5. Neutron Flux: Everywhere but Floor Walls Ceiling Floor

  6. External Shielding (iron)…. Room, mass, space, awkwardness... Need second external veto to tag muons which produce neutrons in the new shielding m 1 MeV neutron 100 MeV neutron ZIP Lead Polyethylene Scintillator Factor of 5 seems doable Rock

  7. Internal Active Veto... Go after other shower fragments; must rebuild inside, make penetrations m 1 MeV neutron 100 MeV neutron Early MC… Factor of 10 possible ZIP Lead Polyethylene Scintillator Rock

  8. MINOS Technology • Iron/Scintillator tracking calorimeters • 4.1 x 1cm scintillator strips, up to 8m long • Extruded polystyrene (co-extruded TiO2 coating) • PPO (1%), POPOP (0.03%) fluors • Readout via wavelength shifting fibres • Kuraray 1.2mm fibre (Y-11 fluor, 175 ppm) • Hamamatsu Multi-anode PMTs • Alternate planes rotated by  90o for 3D hits • Near and Far detectors magnetised

  9. Plan • Monte Carlos underway • Preliminary Results in September

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