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. Rock Scintillator Polyethylene Lead ZIP  100 MeV neutron 1 MeV neutron

5. Neutron Flux: Everywhere but Floor Walls Ceiling Floor

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

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

9. MINOS Technology Iron/Scintillator tracking calorimeters 4.1 x 1cm scintillator strips, up to 8m long –Extruded polystyrene (co-extruded TiO 2 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  90 o for 3D hits Near and Far detectors magnetised

10. Plan Monte Carlos underway Preliminary Results in September