Observed energy dependence of Fano factor in silicon at hard X-ray energies

An experimental evaluation of the Fano factor F in silicon at hard X-ray energies (5.9-136.5 keV) has been performed by means of a low-noise, high charge collection efficiency silicon drift detector with on-chip electronics. A dependence of F from the detector temperature as well as from the energy of the X-ray photons has been found. Assuming a pair creation energy equal to 3.64 eV, at +20 deg. C the F factor was observed to vary from 0.124±0.006 at 5.9 keV up to 0.159±0.002 at 122 keV. At -35 deg. C, the change of F with respect to the photon energy was less remarkable but nevertheless statistically significant, from 0.123±0.002 at 5.9 keV up to 0.134±0.001 at 122 keV. To our knowledge, the present results represent the first experimental evidence of an energy dependence of the Fano factor in silicon at hard X-ray energies