Post on 20-Jan-2016
transcript
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…• 1 order suppression would be welcome (>2
orders by move to SNOlab)
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
RockScintillator
Polyethylene
Lead
ZIP
100 MeVneutron
1 MeVneutron
Neutron Flux: Everywhere but Floor
WallsCeiling
Floor
External Shielding (iron)…. Room, mass, space, awkwardness...
RockScintillator
Polyethylene
Lead
ZIP
100 MeVneutron
1 MeVneutron
Factor of 5 seems doable
Need second external veto to tag muons which produce neutrons in the new shielding
Internal Active Veto...Go after other shower fragments; must rebuild inside, make penetrations
RockScintillator
Polyethylene
Lead
ZIP
100 MeVneutron
1 MeVneutron
Early MC…
Factor of 10 possible
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
Plan
• Monte Carlos underway• Preliminary Results in September