Study On The Radiation Effect Of Binary Diacetylene Gel Composites

Absorbed dose control is a key factor to irradiation quality in nuclear industry. The precise measurement is required to insure the absorbed dose of substance irradiated as expectation. Moreover, three-dimensional dose calibration is needed in the radiation processing, stereotactic radiotherapy and some scientific experiments requiring narrow or special-shaped space. Thus the dosimeter with the feature of 3-dimension, high precision, sensitiveness and plasticity is requisite.At present, the common dosimeters are calorimeter, ionization chamber dosimeter, fricke dosimeter, free radical dosimeter, thin-film dosimete. Compared with the dosimeter listed above, gel dosimeter is superior for its smaller volume, easier fabrication, more convenient for testing. Moreover, gel dosimeter could be used in a narrow or special-shaped space for 3-dimentional dose calibration prospectively.The diacetylene, in this thesis, is 10,12-pentacosadiynoic acid. It will polymerized after y-irradiation which leads to radiochromic. Absorbance changes can be used to represent the absorbed dose due to the reason that the absorbance response of diacetylene is correlated to the absorbed dose. Based on this feature, the gel with diacetylene is fabricated for dose calibration. The diacetylene is put into rotary evaporator evaporation for film-forming, then it is self-assembly to be vesicles by ultrasound with deionized water. The vesicles will be immobilized in the gel system to obtain the composite materials. The samples are irradiated by 60Co-y source, the radiation reaction mechanism of diacetylene was studied. And the dose response, dose rate effect, radiation post-effect, temperature effect and the diffusing effect of the composite materials have been also researched. The main conclusions are as follows:1. Degradation appears in agarose gel during irradiation, its mechanical strength decreases as absorbed dose increases. Chemical structure of the agarose gel is relatively stable, only small amount of harmless gases generate and carbonyl group is observed. For the acrylamide gel secondary-crosslinking takes place during irradiation at first. And it begins to degrade when the absorbed dose increases after 5 kGy. The structure is stable enough which is proved by the fact that no functional group generates after irradiation, and only few amount of harmless gases generate.2. It indicates from studying the radiochromic mechanism of diacetylene vesicles after irradiation that the free radicals such as ·H or·OH radiolysis from the water in vesicles fluid give rise to polymerization reaction of diacetylene monomers, along with the molecular structure transition from π-π conjugate of O≡C-C≡C to large π conjugate of [C≡C-C=C]n. That is the reason for radiochromic of diacetylene vesicles. The absorption peak of diacetylene vesicles after y-ray irradiation is around 660 nm, its absorbance increases as absorbed dose increases, The fact that characteristic absorption of Raman spectrum migrates to lower wave number can be attributed to decrease of molecular vibration energy level caused by extending of conjugated system as absorbed dose increases.3. Both the composite materials composed of agarose gel and acrylamide gel have a good linear response at a certain range (500～2000 Gy for agarose composite materials and 50～2000 Gy for acrylamide composite materials). Dose response is independent of dose rate (0.1～40 Gy/min). The post-effect of samples are not obvious, and the absorbance keeps unchanged after 24 hours. Meanwhile, dose responses of the two composite materials are not affected with fractionated irradiation. But the dose responses are closely related to temperature.4. The area irradiated by the electron beam of composite materials does not lateral move after 48 hours. It means that diacetylene vesicles are not subjected to diffusion for that they are immobilized in gel system. Therefore, discetylene gel composite materials can be used to record dose distribution in 3-dimensional space accurately.5. The composite materials with diacetylene vesicles as the color developing agent have been prepared successfully for the first time in this work. It has a good linear response to y-ray in a certain range, which provides a potential method of the development on gel dosimeter.