A microcollimated ion beam facility for investigations of the effects of low-dose radiation.

Charged-particle microbeams are unique tools to mimic low-dose exposure in vitro by delivering a defined number of particles to single mammalian cells down to only one particle per cell or group of cells. A horizontal single-ion microbeam facility has been built at the INFN-Laboratori Nazionali di Legnaro 7 MV Van de Graaff accelerator. Different light ions (1H+, 2H+, 3He2+, 4He2+) are available covering a wide range of LET from 7 to 150 keV/microm. Collimators of different geometries and materials have been tested, and beam spots 2-3 microm in diameter have been obtained using a tantalum disc. Cell visualization and recognition are performed with a phase-contrast optical microscope coupled with dedicated software. One unique characteristic of such a system is that neither cell staining nor UV light is used. Cells are automatically positioned on the beam spot through remotely controlled precision XY translation stages. A particle detector is positioned downstream of a specially designed petri dish to perform energy measurements and count particles crossing the cell. A particle counting rate of less than 1 ion/s can be reached. This feature, combined with a fast beam deflection system, ensures high reproducibility in administering a preset number of particles per cell.