A feasibility study of a silicon solid-state microdosimeter

Solid-state silicon detectors are challenging devices for microdosimetry, mainly because they can provide sensitive zones (i.e. depletion layers) of the order of a micrometer. This type of detector can be realized by placing a tissueequivalent converter in contact with a silicon device. A semiconductor microdosimeter is characterized by a high spatial and a good energy resolution and could be used for in-vivo measurements on a patient undergoing radiation therapy. However, it may present some limitations, such as: (i) the minimum detectable energy which is ruled by the electronic noise; (ii) radiation hardness; (iii) the geometry of the sensitive volume, which is usually parallelepiped (and not spherical like in conventional microdosimeters, such as the Rossi counter); (iv) the fieldfunnelling effect; (v) the non tissue-equivalence of silicon. The use of semiconductor detectors for microdosimetry was firstly proposed in ref. [1] and further investigated in refs. [2-4]. A deep study of such a device was carried out in ref. [5]. The present work discusses the use of commercial semiconductor detectors for microdosimetry. The following items are investigated: (i) contribution of the secondary charged particles (starters) generated directly in silicon; (ii) field-funneling effect; (iii) dimensions and geometry of the depletion layer and effects due to the non tissue-equivalence of silicon.