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 en ergies (5.9-136.5 keV) has been performed by means of a low-noise, high cha rge 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 degrees C the F factor was observed to vary from 0.174 +/- 0.006 at 5.9 keV up to 0.159 +/- 0.002 at 122 keV. Ar -35 degrees C, th e change of F with respect to the photon energy was less remarkable but nev ertheless 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 facto r in silicon at hard X-ray energies. (C) 1999 Elsevier Science B.V. All rig hts reserved.