Chemical Dosimetry in the "Water Window": Ferric Ions and Hydroxyl Radicals Produced by Intense Soft X Rays.

A standard Fricke dosimeter was used to measure the absorbed dose via the oxidation yields of Fe ions in an aqueous environment induced by soft X rays within the "water window" spectral range. We also exploited the property of a neutral solution containing terephthalic acid as a tool for selective detection of OH radicals. Both dosimetric systems were irradiated using the experimental pulsed laser-plasma soft X-ray source as well as conventional 1.25-MeV gamma rays. Radiation chemical yields of Fe ions and OH radicals were determined to be (5.13 ± 0.94) × 10 µmol·J (4.95 ± 0.91 100eV) and (2.33 ± 0.35) × 10 µmol·J (0.23 ± 0.03 100eV), respectively. Measurements were supported by Monte Carlo simulations to estimate the linear energy transfer of the water window radiation. The simulation results are in good agreement with expected linear energy transfer of ions inducing the same Fe ion and OH radical radiation chemical yield.