Aerogel Efficiencies of Threshold Cherenkov Counters

We present the aerogel efficiencies of the Cherenkov counters used as a sub-component of Bates large acceptance spectrometer toroid. The events of the elastic channel of electron-proton scattering from hydrogen is utilized. The counters' aerogel efficiencies change between (91.5 +/- 0.3) and (98.6 +/- 0.6)% based on a time-of-flight scintillation paddle. In addition, up to similar to 7 % variation in the local efficiencies per paddle is attributable to statistical fluctuations and no local inefficient aerogel pockets are encountered.