Radiochromic films (GafChromic DM 1260 and MD 55), consisting of thin, colorless transparent coatings of a polycrystalline, substituted-diacetylene sensor layer on a clear polyester base, are studied by pulse radiolysis and flash photolysis, in terms of the kinetics of their response to ionizing radiation and ultraviolet light, respectively. These films have recently been established for broad applications in radiographic imaging, nuclear medicine, and dosimetry for radiotherapy, blood irradiation, insect population control, food irradiation, and industrial radiation processing. The radiochromic reaction is a solid-state polymerization, whereby the films turn deep blue proportionately to radiation dose, due to progressive 1,4-trans additions as polyconjugations along the ladder-like polymer chains. The pulsed-electron-induced propagation of polymerization has an observed first-order rate constant of the order of 103 s-1, depending on the irradiation temperature (activation energy ≈ 50 kJ mol-1). The UV-induced polymerization is faster by about one order of magnitude (kobs = 1.5 × 104 s-1). In the case of the electron beam effect, the radiation-induced absorption spectrum exhibits a much slower blue-shift of the primary absorption band (λmax=675 nm → 660 nm) on the 10-3 - 10+1 second time scale. This effect is attributed to crystalline strain rearrangements of the stacked polymer strand units.
|Number of pages||16|
|Journal||ACS Symposium Series|
|Publication status||Published - Dec 1 1996|
ASJC Scopus subject areas
- Chemical Engineering(all)