Figure 1(b) is a photograph of the back of the two samples shown in Figure 1(a). The difference
in color between irradiated and nonirradiated samples is far less pronounced.The nominal cross sectional thickness of the filmsonthe slide is about 0.75mm(Figure 1(c)). Examination of the film cross sections with a light microscope (Olympus BX43) suggests that the color change penetrates less than 20% of the film thickness.