Electron trapping in frozen gels γ-irradiated at 77 K

White, opaque samples of frozen polydextran gels (Sephadex G-25, Pharmacia) turn intensely blue under γ-irradiation at 77 K in the dark. The dark blue colour is pretty stable for a few days in the dark at 77 K. It disappears, however, in seconds, at sunlight and/or upon warming. Subtracting the ESR spectrum left after the photobleaching from the initial spectrum one obtains a singlet with half-width of about 14.5 ± 1 G and g equal to about 2.0018. If heavy water is embedded into the polydextran gel one obtains by the same procedure a singlet with half-width of ≈ 3.8 ± 1 G, and g equal to 2.0018. The maximum of the optical absorption is at about 575 nm, which corresponds to 2.16 eV. The radiation yield of electrons in fully swollen polydextran gel, containing about 73% of water, is equal to about 0.4.