Microscopic evaluation of the absolute fluence distribution of a large-area uniform ion beam using the track-etching technique

The absolute fluence distribution of a large-area uniform beam was investigated microscopically via track etching of an Ar-irradiated polyethylene terephthalate (PET) film. The irradiated sample was divided equally into 64 pieces, for each of which the track-pore densities were counted over a 12 × 17 μm2 microscopic area near the center. For comparison, the relative intensity distribution was obtained by measuring the optical density of a similarly irradiated Gafchromic film at a resolution of 500 × 500 μm2 and then taking the measured value at the center of each of the 64 areas. The relative standard deviations of the distributions were in good agreement despite the difference in the observed resolution area and the small sample number. It was, therefore, confirmed that track etching is a reliable technique for evaluating absolute fluence and that a uniform intensity distribution of the beam was microscopically realized.