Experimental limitations in microdosimetry measurements using the variance technique

Microdosimetry measurments give information about the energy imparted to a volume of given size. With the most frequent method only data for object sizes above 0.2 μm are obtainable. Although restricted to the dose mean values, the variance technique can, however, be applied to object sizes an order of magnitude less. In this report some limiting parameters for this technique are discussed and results down to about 20 nm in a 60Co γ-ray beam are reported. The resulting data exceed earlier reported valued at object sizes below 0.1 μm, but are in good agreement for larger object sizes. (orig.)