Response of the peeled off Gafchromic EBT2 film to 4 MeV alpha particles using transmission and reflection modes

Abstract

The dose-response and spatial resolution of the peeled-off Gafchromic EBT2 films irradiated with different doses of 4 MeV alpha particles were characterized using transmission-and-reflection scanning modes of a flatbed scanner. The Edge Spread Function (ESF) was produced by positioning a razor blade with a sharp edge directly on the film's active layer to minimize the penumbra. Subsequently, 4 MeV alpha particles were incident normally on the setup, producing two distinct regions on the film. The irradiated peeled-off Gafchromic EBT2 films with 4 MeV alpha particles were digitized using a flatbed scanner in both transmission and reflection modes under identical conditions. In reflection mode, the red and green channel pixel values exhibited a more rapid decay compared to those in transmission mode. The edge spread function (ESF) data was fitted using an error function, and which is then differentiated to obtain the line spread function (LSF). In transmission mode, the Weber contrast increased significantly with dose, compared to the reflection mode. For the peeled-off Gafchromic EBT2 film, the spatial resolution in terms of full width at half maximum (FWHM) shows a slight dose independence on 4 MeV alpha particle doses for all color channels in transmission mode, but it is slightly correlated with the reflection mode. In both transmission and reflection scanning modes, the green channel exhibits the highest spatial resolution. The spatial frequency was determined at the half-maximum of the modulation transfer function (MTF-50), with the green channel yielding the highest spatial frequency in both modes.