Hi Raymond, I should to say you, that mineral with such composition hadn't any chance to be plumbobetafite even according to Hogarth' nomenclature. It was betafite according to it. Of course if it is cubic, i.e. is member of pyrochlore supergroup at all. It may be some orthorhombic uranium titanate. Do you have complete analysis of your mineral? What is it locality? How it looks?