Cold Finger of Cryostat Micro Balance U=OkVT≈4K Thickness Detection of frozen van der W怕als Gas Layer Primary u Beam E≈4MeV Radiation Shield Muon Trajectories red:slow u,E≈15keV Moderator Frame (U15kV) blue:fast,unmoderated u Moderator:370 um Si Guard Ring (U≈12kW) 1st electrostatic Grid (U10kv) 2nd electrostatic Grid (U=0kV)