Absolute calibration of GafChromic film for high-flux laser-driven ion beams*

We report on the calibration of GafChromic HD-v2 radiochromic film at extremely high dose up to 100 kGy. The absolute calibration was done with nanosecond ion bunches at the Neutralized Drift Compression Experiment II (NDCX-II) at Lawrence Berkeley national laboratory (LBNL) with doses ranging from 100 to 100 kGy. The films were scanned using EPSON V600 scanner in separate RGB channels, as well as Grayscale channel. An absolutely calibrated optical density filter was used as a reference to transfer our one-time absolute calibration curve to different experimental setups. The calibration curve is further applied to a laser driven ion experiment at the BELLA petawatt laser facility at LBNL, to reconstruct the spatial and energy distribution of the laser-accelerated proton beams. The result was compared to the measured spectrum with a Thomson spectrometer using microchannel plate as the detector, showing fair agreement in proton beam energy and intensity.