【作者】 王鹏；

【导师】 林理彬；

【作者基本信息】 四川大学 ， 辐射技术及应用， 2001， 硕士

【摘要】 本文介绍了正电子湮没技术，以及物质的辐照效应基础，并采用正电子湮没寿命谱的方法对透明陶瓷MgAl₂O₄缺陷特性进行了研究。 透明陶瓷MgAl₂O₄是多功能材料，因它既是一种透明材料，又是一种抗辐照材料，因此它在红外激光窗口，红外制导导弹球罩以及在高温或强辐射下工作的照相机镜头等领域广泛的应用。作为一种新兴的材料其应用前景十分广阔。 在其作为窗口使用时，它的透过性和抗辐照性决定其性能的好坏，而透过性和抗辐照性跟它内部的缺陷情况有很大的关系。正电子湮没寿命谱技术作为一种专门研究物质内部缺陷的技术，对样品内缺陷的变化十分敏感，因此采用这种技术对不同情况下透明陶瓷MgAl₂O₄内缺陷的变化进行了详细的研究。 实验发现由于透明陶瓷MSAl₂O₄中存在晶粒间界，晶粒间界的寿命与辐照损伤缺陷的寿命值混在一起，造成透明陶瓷MgAl₂O₄和晶体MgAl₂O₄的τ₂值呈现不同的变化特性。 在对样品进行电子，质子，γ射线的辐照后发现了在材料中存在大量正离子空位。对于不同剂量的了射线辐照，透明陶瓷MgAl₂O₄中的缺陷变化存在三个阶段，对应于缺陷的产生，聚积和部份分解。对于经三种射线辐照后的样品进行退火试验，发现在250℃左右时，缺陷发生分解，继续升高退火温度缺陷又重新聚积，最后在500℃左右消失。这说明三种射线在样品中产生的缺陷类型十分相似，因而呈现相似的退火特性。 在对掺La的非化学配比的样品进行研究时，我们发现在化学配比Al₂O₃／MgO=2.3时，由于样品中存在较多的阳离子空位，部分La被掺入空位中去了，因而出现空位填充现象，而在化学配比Al₂O₃／MgO=2的样品中未发现空位填充现象。 对比化学配比和非化学样品的正电子寿命谱数据，我们得出化学配比的样品比非化学的样品更抗辐照。更多还原

【Abstract】 In this thesis positron annihilation technique and irradiation effect are outlined , and the defects of transparent ceramics MgAl2O4 are studied by positron annihilation lifetime spectra.Transparent ceramic MgAl2O4 is a kind of poly-functional material . Because of its transparent and anti-irradiation it can be used as windows for infrared laser , tips of infrared missile and lens of camera working in high temperature and irradiation environment. As a novel material it can be used in wide range .The quality of MgAl2O4 can be depended on its transparent and anti-irradation capability while it is used as window , and thus depend on the defects in it. Positron annihilation lifetime spectra technique is a special technique useful to research the defects in material . It is so sensitive to defects that we use it to study the transparent ceramics MgAl2O4.We find that there exist some grain boundaries in transparent ceramic MgAl2O4. So the lifetimes of positron of grain boundaries and irradiation defects are mixed up . This make T2 have different changing character for ceramics MgAl2O4 and crystal MgAl2O4.After irradiated by electron , proton and Y -ray there have a lot of cationvacancies in the material . With the dose of Y -ray increasing the defects changing in three stages , this correspond to defects’ creation ,decomposition and coalescence . The samples are annealed after irradiated . At first the defects in samples are decomposed when annealing temperature is 250℃ . With the annealing temperature increasing the defects are recoalesced , and then disappear at 500℃ . This means that after irradiated by electron , proton and y -ray the type of defects created in samples are all similar . So they have similar annealing character .The samples doped with La are studied too . We find that some La atoms are doped into vacancies when Al2O3/MgO is 2.3 and quantity of La lower than 50ppm. But this effect is not fount when Al2O3/MgO is 2 .Comparing the positron lifetime data . We can conclude that the stoichoimetry samples have more ability of resisting against irradiation than the nonstoichoimetry samples and the samples doped with La.更多还原