Applications of First Principles Theory to Inorganic Radiation Detection Materials
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1038-O02-01
Applications of First Principles Theory to Inorganic Radiation Detection Materials David Joseph Singh, H. Takenaka, G. E. Jellison, Jr., and Lynn A. Boatner Materials Science and Technology Division and Center for Radiation Detection Materials and Systems, Oak Ridge National Laboratory, 1 Bethel Valley Rd, Oak Ridge, TN, 37831-6114 ABSTRACT Applications of first principles methods to understand properties of several known and potential scintillators for radiation detection are described. These include results for rare earth and Pb-based phosphates, rare-earth trihalides, ZnO, perovskites and tungstates. INTRODUCTION The development of effective systems for radiation detection applications is an ongoing challenge that is constrained by materials performance. Much research in radiation detection materials has focused on issues of crystal growth and perfection since these are clearly crucial. However, much can also be gained from understanding of trends within different materials families and the specific limitations on performance. These issues can be addressed in part using first principles calculations. Such calculations provide a microscopic window into materials properties that can give chemical insight. This can be of use in finding better materials and guiding modifications of existing materials [1-6]. Here we illustrate this by presenting recent results obtained by applying first principles theory to scintillators used in radiation detection. The calculations reported here were performed using the general potential linearized augmented planewave (LAPW) method [7], mainly within the local density approximation (LDA). This method provides a highly accurate solution of the density functional equations even for open crystal structures with heavy elements. One of the key inputs for such calculations is the crystal structure. However, in complex scintillators there is often uncertainty about the crystal structure, especially for the internal coordinates. This typically arises in scintillators containing both heavy and light elements, which represents a difficult case for x-ray refinement. In such cases, it is possible to obtain the internal coordinates by minimization of the density functional total energy [8,9]. This was done when needed in the examples discussed below. ELECTRONIC STRUCTURES One of the most useful ways of understanding trends in properties of materials is via the electronic structure. Moreover, in scintillators, electronic structure is directly related to scintillator performance, particularly activation and energy transport. We begin with a brief overview of work on the electronic structure of Pb and non-Pb containing phosphates [4]. Phosphate Scintillators: Activation of Pb-Based Glasses Various phosphates such as LuPO4 can be readily activated with Ce3+ and other rare earths to produce good crystalline scintillators. While there are related Pb-based orthophosphate and pyrophosphate materials, it is not known whether these can be the basis of good scintillators or how this might be ac
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