Single-ion microbeam as a tool for low-dose radiation effects investigations

Abstract

Practical assessment of human radiation exposure risk deserves particular attention especially for low doses (and low dose rates), which concern environmental and occupational exposure. At these dose levels ionizing radiation exposures involve mainly isolated charged particle tracks, which strike individual cells at time intervals averaging from weeks to several years apart. Accelerator-based microbeam irradiation technique offers a unique tool to mimic such an exposure, allowing irradiating single cells individually with micrometer precision and with a preset number of charged particles down to one particle per cell. A horizontal single-ion microbeam facility for single-cell irradiations has been designed and set up at the INFN-LNL 7MV CN Van de Graaff accelerator. The light ion beam is collimated in air down to a section of 2-3µm in diameter by means of appropriate pinholes. Semi-automatic cell visualization and automatic cell positioning and revisiting system, based on an inverted phase contrast optical microscope and on X-Y translation stages with 0.1µm positioning precision, has been developed. An in-house-written software allows to control remotely the irradiation protocol. As a distinctive feature of the facility, cell recognition is performed without using fluorescent staining and UV light. Particle detection in air, behind the biological sample, is based on a silicon detector while in-air beam profile and precise hit position measurements are accomplished by a custom-made cooled-CCD camera and Solid State Nuclear Track detectors, respectively. A particle counting rate of less than 1 ion/sec can be reached.