Fast scintillation counters with WLS bars

The Do/ collaboration is building 4608 scintillation counters to upgrade forward muon system for the next Fermilab Collider run. Each counter consists of 12.7 mm thick scintillator plate with two WLS bars along two sides for the light collection. With average ${10}^2$ photoelectrons from mip particle the counters provide time resolution below $\text{1ns}$ and have good energy resolution. Results of Bicron 404A scintillator and Kumarin 30 WLS aging under irradiation up to $\text{3Mrad}$ are presented. With specially designed magnetic shielding counters can operate in magnetic filed up to $\text{500G.}$