When a high-energy photon ejects an inner shell electron, an electron from a higher shell can cascade down to fill the vacancy. The energy released in this cascade can potentially eject a second electron, allowing a single ionizing photon to produce two or more photoelectrons. Although this effect was discovered first by Lise Meitner, it is named after what other physicist who also lends his name to the world's largest cosmic ray observatory?
Pierre Victor Auger