Time Resolution of a Scintillation Counter System

Time resolution of a scintillation counter system composed of scintillator, light pipe, multiplier phototube, discriminator, and coincidence circuit is discussed. The discriminator and coincidence circuits can produce coincidence curves with edges as steep as 10 psec per decade. Multiplier phototubes are capable of similar resolution. providing they view sufficiently bright, well-defined light flashes. In a time-of-flight measurement at the Berkeley 184-inch Cyclotron, the coincidence curve slope, measured from a counting rate of 50% to 5%, is 400 psec per decade. The light level corresponds to 2000 electrons reaching the first dynode of the multiplier phototube. A slope of 200 psec per decade would be expected if only the multiplier phototube and electronics were considered. Geometry and rate of light output of the scintillator are believed to limit system resolution at present.