A micrometric thickness silicon diode proposed as a microdosimeter

A thin silicon diode formed by a deep p⁺ implantation under a shallow n⁺ one is proposed as a solid state microdosimeter. The thickness of the sensitive volume of the tested device is about two micrometers and the active area is about ten millimeters square. Due to the very large electric capacitance of the diode (about 1 nF) a low noise read-out circuit based on a discrete JFET has been developed. The noise due to the parasitic resistance of the detector itself dominates and fixes the lower threshold of the energy spectrum. A prototype of the proposed microdosimeter covered with a polyethylene converter has been irradiated with fast monoenergetic neutrons at the INFN-Legnaro Labs (I). The first experimental spectra are in good agreement with the simulated ones. The effect of direct interactions of thermal neutrons in silicon has been measured.