Figure 4.

Paint irradiation of a designated circular area with a focused microbeam. A focused carbon-ion microbeam (26.7 MeV/u, LET = 80 keV/$\mathsf{\mu }$m) was used to irradiate the CR-39 ion track detector film with paint irradiation technology so that a circular area was exposed to a dose of 0.1 to 2.5 Gy. The focused beam spot used for irradiation was 5 $\mathsf{\mu }$m in diameter. The irradiated CR-39 films were treated with an alkaline solution to visualize the trajectory, and it was confirmed that the ions hit the entire designated area uniformly. (a) Paint irradiation of a circular area with a focused microbeam at 0.1 Gy. (b) Paint irradiation at 0.5 Gy. (c) Paint irradiation at 2.5 Gy. (d) Irradiation of carbon ions equivalent to 0.1 Gy with a beam spot formed by a collimated microbeam with a pinhole of 250 $\mathsf{\mu }$m in diameter.