Abstract
Purpose
To introduce and characterize a new “reverse‐Fricke” radiation reporting system utilizing the reduction of ferric ions (Fe3+) to ferrous ions (Fe2+).
Methods
Two formulations of the radiochromic reporting system, referred to as A and B, were prepared for investigation. Formulation‐A consisted of 14 mM 1,10‐phenanthroline, 42 mM ethanol, and 57 mM ammonium ferric oxalate in water. Formulation‐B consisted of 27 mM 1,10‐phenanthroline, 42 mM ethanol, and 28 mM ammonium ferric oxalate in water. Solutions were prepared immediately prior to irradiation with a Cobalt‐60 unit with radiation doses of 0, 1, 5, 10, 15, 20, and 25 Gy. The change in optical density over the visible range of 450–650 nm was measured using a spectrophotometer immediately after irradiation. The effective atomic numbers of the formulations were calculated using Mayneord's formula.
Results
Ionizing radiation energy absorbed in the solutions causes the reduction of ferric ions (Fe3+) into ferrous ions (Fe2+), which then forms a 1:3 red colored complex with 1,10‐phenanthroline ([(C1 2H8N2)3Fe]2+) that can be measured spectrophotometrically. The absorbance spectra of the resulting complex displayed a peak maximum at 512 nm with a greater change in absorbance for Formulation‐B after receiving comparable radiation doses. The change in absorbance relative to dose exhibited a linear response up to 25 Gy for both Formulation‐A (R2 = 0.98) and Formulation‐B (R2 = 0.97). The novel formulations were also nearly water equivalent (Zeff = 7.42) with effective atomic numbers of 7.65 and 7.52 and mass densities within 0.2% of water.
Conclusion
Both formulations displayed visible Fe2+ complex formation with 1,10‐phenanthroline after irradiation using a Cobalt‐60 source. The higher sensitivity measured for Formulation‐B is attributed to the increase in 1,10‐phenanthroline concentration and the increase in the 1,10‐phenanthroline to ammonium ferric oxalate ratio. Further investigation of this radiation reporting system in a 3D matrix material is encouraged.
NSF GRFP Grant Award #LH‐102SPS