Irradiation system of ions (H-Xe) for biological studies near the Bragg peak

We have developed a new system for irradiating biological samples in air with ions from H to Xe below 6.0 MeV/nucleon near the Bragg peak. The irradiation system can provide ion beams with 20-mm diameter of which the central area of 100 mm2 is uniform in fluence rate within a standard deviation of ±10%. For each ion, the linear energy transfer is selectable by irradiation positions in air, from the lowest at the surface of a vacuum window to the highest at the Bragg peak, for example, from 281 to 977 keV/μm for C ions. A wide range of fluence rates, 10-3-104 ions/μm2/s, can be provided by the system, which makes it possible to irradiate a variety of biological samples with different target sizes, from small plasmid DNA to living mammalian cells. The ion fluence irradiated to each sample is calculated from the output of the secondary electron monitor using the linear relationship between the output and ion fluence measured at the sample position by CR-39 track detectors. Survival curves and visualization of NBS1 foci for human cells are presented as examples of preliminary experiments using C ions near the Bragg peak