Biological response to inner-shell ionization

Inner-shell ionization and the subsequent x-ray and Auger-electron cascades resulting from the filling of inner-shell vacancies play important roles in radiation biology. These processes are useful as tools for enhancing our understanding of the basic mechanisms of biological response to radiation, as well as being important in biological imaging and radiation therapy. Radioisotopes, such as 125I, that form inner-shell vacancies by electron capture and internal conversion processes, are found to be the short particulary effective in producing biological damage. Because of the short range of Auger electrons emitted in the filling of inner-shell vacancies the degree of biological response is strongly dependent of the position of the radionuclide relative to the sensitive elements of the cell. For example, when incorporated into the DNA of a cell the decay of 125I can be more damging than the passage of a high linear energy transfer (LET) alpha particle