Fast scintillation counters for the DO muon system upgrade

The design and main parameters of the completly redesigned DO Forward Angle MUon System (FAMUS: 1.0 < \eta\ < 2.0) for the next high luminosity Tevatr on Collider run are reported. Results of the studies of trigger scintillati on counters based on fast scintillator Bicron 404A and WLS bars SOFZ-105 ar e presented. We report about results of test beam studies of prototype coun ters including minimum ionizing particles detection efficiency, time resolu tion and amplitude response. Radiation ageing of scintillating materials fo r the doses up to 1 Mrad, phototubes magnetic shielding in the fields of up to 700 G and ageing of phototubes are presented. All tests show robustness of scintillation counters as triggering detector of the new muon system fo r a long period.