Auger effect in medicine The Auger effect refers to the ejection of electrons from an atom following ionization of inner-shell electrons It is usually initiated by X-ray photoionization of K-shell or L- shell electrons. In heavy high-Z atoms up to 20 Auger electrons may be ejected (see Table 5.3 of Atomic Astrophysics and Spectroscopy (AAS) Pradhan and Nahar, Cambridge University Press, 2011) Special cases of Auger transitions are known as Coster-Kronig and Super-Coster-Kronig transitions (see Fig of AAS, as animated in the second slide) It may be highly effective in cancer treatment using high-Z material or nanoparticles delivered to the tumor and irradiated by X-rays (animated in the third slide) Auger electrons from high-Z atoms can kill malignant cells

Auger Radiation and Electron cascades Incident photon hits the K-shell Electron absorbs the photon The electron gets ejected, leaving a vacancy The vacancy in the K shell is filled with an L-shell electron, creating a new vacancy The L-shell electron then emits a Kα photon, which can leave as fluorescence, or knock out another L-shell electron We now have 2 vacancies in the L- shell that will be filled with M-shell electrons The two M-shell electrons can emit two photons, which can then knock out two more M-shell electrons This leaves us with four vacancies in the M-shell that will continue this increasing cascade of electron ejection throughout the atom (“Atomic Astrophysics and Spectroscopy”, Anil Pradhan & Sultana Nahar, Cambridge U. Press 2011)

Monoenergetic X-Ray Irradiation of High-Z Nanoparticles for Imaging and Therapy: “Resonant Nano-Plasma Theranostics (RNPT)” (Pradhan et. al., Proc. XVth Int. Conf. Comp. Rad., V.2, p89, 2007) Particles absorb X-rays and excite/ionize Burst of monochromatic x-rays X-rays that are transmitted are detected Particles return to the ground state and emit light