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