Growth of a New, Fast Scintillator Crystal for Nuclear Experiments

70631S02-II Rare earth orthophosphate crystals could satisfy the requirements for improved scintillators needed for nuclear physics experiments. These requirements include fast decay time (approximately 30 nsec with no slow component), greater light output compared to current materials, a radiation length less than 2 cm, and the ability to be grown in a large size. All of these requirements could be met at reasonable cost if a suitable solvent system and growth technique could be identified for cerium-doped gadolinium orthophosphate. In this project, a new solvent system will be studied to identify the solution region from which cerium-doped gadolinium orthophosphate can be grown. The solution characteristics and phase relationships for this system will be investigated to determine the feasibility of growing large cerium-doped gadolinium orthophosphate crystals by top-seeded solution growth. In Phase I, fourteen solution compositions were studied to determine the solid phases present. The amount of solid precipitate, its phase composition, and its crystal morphology were determined by x-ray diffraction and microscopy techniques. Conditions for the formation of phase-pure GdPO4 crystals were determined, and small crystals of cerium-doped GdPO4 were grown. Phase II will develop and optimize a top-seeded solution growth technique for growing large cerium-doped crystals. The cerium concentration will be optimized for maximum light output. Scintillator elements will be fabricated and polished to determine spectroscopic properties. Commercial Applications and Other Benefits as described by awardee: Cerium-doped gadolinium orthophosphate should have better characteristics than cerium doped gadolinium orthosilicate, which is a major scintillator crystal utilized in positron emission tomography. The growth technology for this orthophosphate crystal would allow the possibility of incorporating a series of rare earth analog crystals into many commercial laser systems.