external exposure facility Alpha particles irradiator Paul Schofield The alpha particle irradiator at ISS Rome uses an americium-241 or polonium source to deliver well-defined high-LET alpha particle doses to cells and biological samples, and is used alongside the LIBIS and Gammacell® 40 facilities in the same department. It has been used to study DNA damage clustering, cell killing and the bystander effect following high-LET irradiation, contributing to understanding of the relative biological effectiveness of alpha particles. The facility supports fundamental radiobiology studies on the mechanisms of action of densely ionising radiation. Located at Istituto Superiore di Sanità. Esposito et al., 2009. Radiat. Res. 172: 632-642