Radiation Chemical and MR Studies of Aqueous Agarose Gels Containing Ferrous Ions.

Aqueous agarose gels containing ferrous ions, in 0.05 N sulfuric acid have been studied after irradiation with 6-18 MeV electrons or ^{137} Cs gamma-rays. Such gels can sustain a radiolytic chain reaction, producing Fe ^{3+} with G(Fe^ {3+})-values up to 100 having been observed. The Fe^{3+} production is independent of dose rate between 0.434 and 3.74 Gy min ^{-1}. Dissolved oxygen is needed to maintain the chain reaction, and initial ferric yields are increased if the gel is oxygen saturated or if the ferrous concentration is decreased below 1 mM. The oxidation of ferrous to ferric alters the magnetic moment of the ion and its electron spin relaxation time, which in turn affects its ability to promote proton spin relaxation rates. Longitudinal proton magnetic relaxation rates are increased in proportion to ferric production, permitting visualization of dose levels in these gels by magnetic resonance imaging (MRI) techniques. Non-uniform dose distribution images of electron irradiated ferrous/agarose (FA) systems have been obtained using MRI. Images of radiation doses surrounding capillary tubes filled with radioactive material embedded in FA systems have also been obtained. In this work, another new method of using the ferrous/agarose gel system doped with xylenol orange to visualize the radiation dose distribution directly by eye has been developed. The color change developed depends both quantitatively and qualitatively on the concentrations of solutes in the gel.