Abstract
After swelling at the short times less than 300s, the specimen became two regions. One is the region where acetone did not diffuse in. The other is swollen by acetone. Take the specimen out till specimen without acetone, and then put the specimen into acetone again. We found that the beautiful pattern at the surface. This pattern has 2-D regular pattern. Surface patterns were analyzed by two-dimensional fast Fourier transform. Then, we can get macro wavelength of the pattern. We studied three kinds of the specimen: non-irradiated specimen, irradiated in air and irradiated in vacuum. We changed parameters like temperature, time, dose and thickness of the specimen. We found that wavelengths of non-irradiated specimen and specimen irradiated in vacuum and in air were increased as immersion time and temperature increased. The wavelength of the specimen irradiated in air is longer than the specimen irradiated in vacuum because of the crystallites formed. We did some measurements of the amplitude of the pattern with time, temperature, dose and specimen thickness. The amplitude was increased as temperature, time, and dose increased but when the time and temperature were large enough, amplitude had a maximum value. We also did some experiments to find whether specimen thickness affects surface morphology. We found that wavelength had a minimum value, and amplitude had a maximum value when specimen thickness increased. We found that the crystallites were increased as time, temperature, oxygen and dose increased. Pattern wavelength and amplitude were affected by crystallization. When the specimen irradiated high dose in the air immersed in acetone, the crack and void were formed. We also found that when thickness of non-irradiated specimen is 0.4-0.6 mm, the crystallites can be formed and 0.8-1.2 mm specimen, no crystallite was observed. The specimens irradiated in vacuum and air also has a similar phenomenon with non-irradiated specimen, but we found some crystallites appear when the 0.4-0.8 mm specimen with 150 kGy irradiated in air.