Fast scintillation counters for the DO muon system upgrade

The design and main parameters of the completely redesigned DO Forward Angle Muon System (FAMUS: 1.0<|/spl eta/|<2.0) for the next high luminosity Tevatron Collider run are reported. Results of the studies of trigger scintillation counters based on fast scintillator Bicron 404 A and WLS bars SOFZ-105 are presented. We report about results of test beam studies of prototype counters including minimum ionizing particle detection efficiency, time resolution and amplitude response. Radiation ageing of scintillating materials for doses up to 1 Mrad, phototube magnetic shielding in field of up to 700 G and ageing of phototubes are presented. All tests show the robustness of scintillation counters as triggering detectors for the new muon system for a long period.