Formation Mechanism Of Radiation Induced Defects In Silica Optical Fiber Material

Optical fiber is being widely used in aerospace, military, nuclear medicine,nuclear industry and other radiation related fields. And the optical fibercommunication in the radiation environment has received more and more attention.The anti-radiation properties of silica optical fiber have also been the internationaland domestic research focus. In order to reduce the radiation sensitivity, it isnecessary to develop the radiation-resistant silica optical fiber. In this dissertation,based on the principle of the interaction of radiation with matter, the formationmechanism of point defects induced by radiation damage in high-purity silica fibermaterial has been analyzed and a kinetic model for point defects has been established.Meanwhile, the characteristics of radiation-induced point defect E’ center in silicaoptical fiber material have been investigated, and influences of pre-irradiation andthermal annealing on E’ center have been studied by experiments. The main contentsare as follows:This paper firstly introduces the principle of electrons and γ-rays interact withmatter, discusses the microstructure characteristics of materials and the formationmechanism of point defects, and reviews the atomic structure of several basic pointdefects induced by radiation in silica optical fiber material.Secondly, the formation mechanism of E’ center induced by energetic particleirradiated in silica optical fiber material is analyzed in detail. According to thisformation mechanism of E’ center, a kinetic theory model has been established, thatis creation plus activation kinetic model. The formation dynamic process of E’centers is discussed. The relation of E’ center concentration changing with irradiationdose is obtained theoretically. For the low-energy particles, E’ centers are formedmainly by pre-existing defects. For high-energy particle, the production of E’ centerincludes two processes creation and activation. The cleavage of strained bonds or oxygen replacement in silica networks lead to the creation of new defects. Thepre-existing defects produce the activation.Then using electron spin resonance (ESR) spectroscopy and optical absorptionspectroscopy, the radiation characteristics of the silica optical fiber material havebeen investigated. The experimental results show that the point defect induced byγ-ray irradiation at room temperature in silica optical fiber material is typical E’center. And the E’ center can be effectively repaired by annealing treatment.According to the formation dynamic model of E’ center established in this paper, therelation of the concentration of E’ centers changing with irradiation dose weresimulated. The simulated results are in good agreement with the experimental results,which indicates that the model is effective.At last, the influences of pre-irradiation and thermal annealing on the radiationcharacteristic of the silica optical fiber material have been investigated by measuringESR spectra and optical absorptions. The results show if silica optical fiber materialhas been treated by pre-irradiation and subsequently thermal annealing, the radiationsensitivity can be reduced effectively when irradiated again. That is to say, theconcentration of E’ defect induced by irradiated again can be decreased effectively.The anti-radiation characteristics can be improved significantly. And the E’ defectconcentration is related with the annealing temperature. When the annealingtemperature is higher than a certain temperature, the concentration of E’ center candecrease rapidly.This paper has studied the formation mechanism of point defects induced byradiation damage in silica optical fiber material and explored through the method ofpre-irradiation and subsequent thermal annealing to decrease the generation of pointdefects. The results provide a theoretical basis not only for improving anti-radiationcharacteristics of the silica optical fiber material, but also for preparing theradiation-resistant silica optical fiber.