Impact of charge collection efficency and electronic noise on the performance of solid state 3D-microdetectors.

Microdosimetry has been traditionally performed through gaseous proportional counters, although in recent years different solid state microdosimeters have been proposed and constructed for this task. In this paper we analyze the response of solid state devices of micrometric size with no intrinsic gain developed by CNM-CSIC (Spain). There are two major aspects of the operation of these devices that affect the reconstruction of the probability distributions and momenta of stochastic quantities related to microdosimetry. On one side, for micrometric volumes, the drift and diffusion of the charge carriers gives rise to a partial charge collection efficiency in the peripheral region of the depleted volume. Such effect produces a perturbation of the reconstructed pulse height (i.e. imparted energy) distribution with respect to the actual microdosimetric distributions. The relevance of this deviation depends on the size, geometry and operation conditions of the device. On the other hand, the electronic noise from the single event readout set-up, poses a limit on the minimum detectable lineal energy when the microdosimeter size is reduced. The article addresses these issues to provide a framework on the physical constraints for the design and operation of solid state microdosimeters.