  In this paper we present new results on electronic emission of Gold
Nanoparticles (GNPs) using X-ray photoelectron spectroscopy (XPS) and compare
them to the gold bulk electron emission. This subject has undergone new
interest within the perspective of using GNPs as a radiotherapy enhancer. The
experimental results were simulated using various models (Livermore and
PENELOPE) of the Geant 4 simulation toolkit dedicated to the calculation of the
transportation of particles through the matter. Our results show that the GNPs
coating is a key parameter to correctly construe the experimental GNPs
electronic emission after X-ray irradiation and point out some limitations of
the PENELOPE model. Using XPS spectra and Geant4 Livermore simulations,we
propose a method to determine precisely the coating surface density of the
GNPs. We also show that the expected intrinsic nano-scale electronic emission
enhancement effect - suspected to contribute to the GNPs radio-sensitizing
properties - participates at most for a few percent of the global electronic
emission spectra of the GNPs compared to gold bulk.
