Micro-collimators fabricated by chemical etching of thin polyallyldiglycol carbonate polymer films exposed to oxygen ions

One approach for α particle radiobiological experiments is to use solid-state nuclear track detectors (SSNTDs) as support substrates to record the α particle hit positions on the targets. To facilitate accurate characterization of the hit positions as well as the incident α particle energies, micro-collimators are required in these experiments to restrict the incident α particles to those with small deviations from normal incidence with respect to the collimator. In the present paper, we fabricated micro-collimators, which restricted α particles to those with deviations as low as 12°. Specially etched polyallyldiglycol carbonate (PADC) films, which are a kind of SSNTD, with a thickness 70 μm were prepared from commercially available PADC films. These were then irradiated by 4.83 MeV/n oxygen ions generated from the heavy-ion medical accelerator in Chiba (HIMAC), Japan. The irradiated films were chemically etched for at least 2.7 h to achieve etched-through air channels to form the micro-collimators. The micro-collimators formed by etching the irradiated films for 2.7, 3.0 and 4.0 h were experimentally shown to be able to restrict α particles to those very close to normal incidence. In contrast, the micro-collimator formed by etching the irradiated film for 4.5 h started to allow α particles with larger deviations from normal incidence to pass through, which is likely due to overlapping of air channels from excessive etching.