RADIATION-DOSE DISTRIBUTIONS IN 3-DIMENSIONS FROM TOMOGRAPHIC OPTICAL-DENSITY SCANNING OF POLYMER GELS .2. OPTICAL-PROPERTIES OF THE BANG POLYMER GEL

A newly developed method of radiation dosimetry makes use of the optic al properties of polymer gels. The dose-response mechanism relies on t he production of light-scattering polymer micro-particles in the gel a t each site of radiation absorption. The scattering produces an attenu ation of transmitted light intensity that is directly related to the d ose and independent of dose rate. For the BANG polymer gel (bis, acryl amide, nitrogen, and gelatin) the shape of the dose-response curve dep ends on the fraction of the cross-linking monomer in the initial mixtu re and on the wavelength of light. At 500 nm the attenuation coefficie nt (mu) increases by. approximately 0.7 mm(-1) when the dose increases from 0 to 5 Gy. The refractive index of an irradiated gel shows no si gnificant dispersion in the visible region and depends only slightly o n the dose. Turbidity difference spectra are compared with theoretical spectra of efficiency factors for total scattering, derived using Mie -Debye theory, and the average sizes of the cross-linked particles pro duced by radiation, as a function of dose, are established. The partic le sizes increase with dose and reach approximately the wavelength of red light. The dependence of the particle sizes on cross-linker fracti on parallels a similar dependence of the water proton NMR transverse r elaxation rate dose response.