  The yield of electrons generated by gold nanoparticles due to irradiation by
fast charged projectiles is estimated. The results of calculations are compared
to those obtained for pure water medium. It is demonstrated that a significant
increase in the number of emitted electrons arises from collective electron
excitations in the nanoparticle. The dominating enhancement mechanisms are
related to the formation of (i) plasmons excited in a whole nanoparticle, and
(ii) atomic giant resonances due to excitation of d electrons in individual
atoms. Decay of the collective electron excitations in a nanoparticle embedded
in a biological medium thus represents an important mechanism of the low-energy
electron production. Parameters of the utilized model approach are justified
through the calculation of the photoabsorption spectra of several gold
nanoparticles, performed by means of time-dependent density-functional theory.
