Demonstration of a time-integrating microdosimeter

A tissue-equivalent spherical proportional counter is used with a modified amplifier system to measure specific energy deposited from a uniform radiation field for short periods of time (on the order of microseconds to milliseconds) in order to extrapolate to dose in sub-micron tissue volumes. The signal is integrated over a variable collection time which is adjusted with a square-wave pulse. Charge from partical passages is collected on the anode during the period in which the integrator is triggered, and the signal decays quickly to zero after the integrator feedback switch resets; the process repeats for every ''triggering'' pulse. Measurements of energy deposited from X-rays are examined. Spectral characteristics as a function of charge collection time are observed and frequency plots of specific energy and collection time-interval are presented. (orig.)