USA

I propose to investigate the chemical interaction between uranyl and a series of porphyrins. Uranyl is an oxygen complex of the heavy element uranium and porphyrins are large, ringlike carbon-based molecules. Several of these chemical complexes have been created in laboratories, and I envisage the results of my research having applications as diverse as nuclear fuel enrichment, radiation detection, cancer therapy, and solar energy. In addition, my work will identify complexes that research chemists should focus their efforts on synthesising in the laboratory as well as demonstrating that state-of-the-art theoretical methods can and must be applied to these complexes in order to give a quantitative understanding of their chemical structure. The porphyrins can be considered as molecular rings, or macrocycles, with a central cavity in which other atoms and molecules can reside, and the variety of applications I have suggested is possible since they can be easily modified in order to change their properties: -Their size can be altered, so that they can be tailored to 'fit' with uranyl to varying degrees. -They can be modified so that they evaporate more readily when heated. -Related macrocycles enable one to choose the type of atom with which the uranyl directly interacts. -They can be altered so that the strength with which they bind uranyl can be varied. An important part of my proposed work is that it is computational: all of my direct research will be via simulation. Simulation plays a greater role in research into the actinide series of elements, which includes uranium, than in other areas of chemistry, since all actinides are radioactive, some of them extremely so, and there are very few facilities in the world where chemists can work with them. This means that less laboratory work can be performed, and so accurate simulation is a requirement in order to further our understanding of these elements. My proposed research employs extremely sophisticated theoretical techniques in order to study uranyl porphyrin complexes. Whilst there has been some previous simulation work on such complexes, it has been carried out using less accurate methods. The realisation of the potential applications that I have outlined are dependent on specific details of the interactions between the porphyrins and the uranyl. Such details are often unavailable directly from experiment; theoretical techniques with strong predictive capabilities are therefore a necessity. In my previous research I have shown that popular theoretical methods may not be capable of even qualitative descriptions of actinide complexes, particularly for the heavier actinides such as plutonium, and it is only in the present day that computational resources are available to conduct simulations capable of quantitative predictions on such relatively large complexes. As part of my proposed research I also intend to study the interactions of the porphyrins with other actinide elements. Other actinides can behave very differently to uranium, and understanding when and how they differ are fundamental questions in heavy element chemistry. The properties of the porphyrins that I have described allow many different aspects of these fundamental questions to be considered. In summary, the significant theoretical study that I propose here will complement the excellent experimental work being carried out both in universities and national laboratories in the United States. Whilst the primary goal of this work is the realisation of the applications I have outlined, it will also set new standards in the simulation of large molecular systems, and deepen our understanding of the chemistry of the actinide series.

Threat reduction and nonproliferation activities urgently require improved radiation detectors. As such, it is vital that we move beyond the largely empirical approach of detector material discovery and optimization. We propose to integrate atomic scale computer simulation and experimental material science, to discover and optimize candidate scintillator detector material compositions. When appropriately coupled, these techniques will create a physics-based feedback loop, which will lead to an approach through which it is possible to optimize the energy resolution of candidate scintillators. Furthermore, this approach is independent of material type (system). Although single crystals are used here to determine scintillator properties, improvements in the understanding and control of defects can be incorporated into other material forms (e.g. nanophosphors or polycrystalline scintillators).While nonproliferation and security activities are beneficiaries of the proposed work, other activities will also directly benefit, such as high resolution radiography for passive evaluation of nuclear power installations. Furthermore, an active industrial market interested in detector development exists for applications such as oil well logging and medical imaging.The general requirements for detector materials are that they are dense (stopping power), bright (conversion of incident radiation energy to light output) and fast (quickly convert the incident energy to light output). While many current detector materials offer some of these properties (e.g. Tl doped NaI is bright and fast but not dense) there are families of compositions that offer improvements, in particular, rare earth oxides (which are much more dense) and halides (which are brighter).The majority of solid state systems for radiation detection require that the incident energy excites an electron that is initially associated with an activator ion embedded in a host lattice. Subsequently, the electron returns to the ground state and light is emitted (that can be detected electronically to produce a signal). This scintillation process depends crucially on the behaviour of the electron (and hole) and hence on the local environment of the activator ion in the crystal as well as the propensity for electrons or holes to become trapped at other defect sites in the lattice. Here three series of host materials and activators will be investigated, as a function of their constituent chemical species, using atomic scale computer simulation and experimental techniques and the results correlated with observed detector efficiency. By predicting defect behaviour, the atomic scale simulations will identify compositional regions of potential significance. Subsequently the experimental work, single crystal growth, luminescence, site selective excitation and Raman spectroscopy, will focus on the specific compositions and determine their properties. This provides a test of the simulation approach in addition to a verification of the efficacy of the materials as luminescence based radiation detectors. The combined approach will allow for a vital, defect property-based optimization, where historically improvements have been empirical.

I propose to investigate the chemical interaction between uranyl and a series of porphyrins. Uranyl is an oxygen complex of the heavy element uranium and porphyrins are large, ringlike carbon-based molecules. Several of these chemical complexes have been created in laboratories, and I envisage the results of my research having applications as diverse as nuclear fuel enrichment, radiation detection, cancer therapy, and solar energy. In addition, my work will identify complexes that research chemists should focus their efforts on synthesising in the laboratory as well as demonstrating that state-of-the-art theoretical methods can and must be applied to these complexes in order to give a quantitative understanding of their chemical structure. The porphyrins can be considered as molecular rings, or macrocycles, with a central cavity in which other atoms and molecules can reside, and the variety of applications I have suggested is possible since they can be easily modified in order to change their properties: -Their size can be altered, so that they can be tailored to 'fit' with uranyl to varying degrees. -They can be modified so that they evaporate more readily when heated. -Related macrocycles enable one to choose the type of atom with which the uranyl directly interacts. -They can be altered so that the strength with which they bind uranyl can be varied. An important part of my proposed work is that it is computational: all of my direct research will be via simulation. Simulation plays a greater role in research into the actinide series of elements, which includes uranium, than in other areas of chemistry, since all actinides are radioactive, some of them extremely so, and there are very few facilities in the world where chemists can work with them. This means that less laboratory work can be performed, and so accurate simulation is a requirement in order to further our understanding of these elements. My proposed research employs extremely sophisticated theoretical techniques in order to study uranyl porphyrin complexes. Whilst there has been some previous simulation work on such complexes, it has been carried out using less accurate methods. The realisation of the potential applications that I have outlined are dependent on specific details of the interactions between the porphyrins and the uranyl. Such details are often unavailable directly from experiment; theoretical techniques with strong predictive capabilities are therefore a necessity. In my previous research I have shown that popular theoretical methods may not be capable of even qualitative descriptions of actinide complexes, particularly for the heavier actinides such as plutonium, and it is only in the present day that computational resources are available to conduct simulations capable of quantitative predictions on such relatively large complexes. As part of my proposed research I also intend to study the interactions of the porphyrins with other actinide elements. Other actinides can behave very differently to uranium, and understanding when and how they differ are fundamental questions in heavy element chemistry. The properties of the porphyrins that I have described allow many different aspects of these fundamental questions to be considered. In summary, the significant theoretical study that I propose here will complement the excellent experimental work being carried out both in universities and national laboratories in the United States. Whilst the primary goal of this work is the realisation of the applications I have outlined, it will also set new standards in the simulation of large molecular systems, and deepen our understanding of the chemistry of the actinide series.

The solid rocks within Earth's interior can flow, analogous to ice in a glacier, given sufficient time and temperature. This flow, or viscous deformation, has a strong influence on a variety of processes over short and long time scales. Over long time scales, the viscous deformation of rocks controls the motion of Earth's tectonic plates. Over short timescales, the viscous deformation of rocks controls the rate at which stresses buildup on overlying, earthquake-generating faults. However, there are major gaps in our understanding of how these rocks deform, which results in significant uncertainties in modeling these large-scale processes on Earth. One of the largest sources of uncertainty is in understanding how grain boundaries, that is the regions between crystals, deform at extreme conditions. This lack of understanding has major implications for predicting processes in Earth. For instance, if grain boundaries are weak relative to the interiors of crystals, then the rates at which stresses build up on large, earthquake-generating faults may increase tenfold. To address this shortcoming, we will carry out experiments at extreme conditions in which we slide two crystals past each other. In some cases, we will add water to the boundary to test if water increases how fast the crystals slide. The data from many experiments will be used to create an equation that describes how fast the crystals slide under a wide range of conditions. To investigate how individual grain boundaries influence the properties of a rock made up of many crystals, these equations will be incorporated into numerical simulations that predict the behavior of an aggregate of crystals. These simulations will be used to understand the importance of grain boundaries in a variety of important large-scale geologic processes.