The half-life of uranium-238 is about 4.5 billion years, uranium-235 about 700 million years, and uranium-234 about 25 thousand years. Uranium atoms decay into other atoms, or radionuclides, that are also radioactive and commonly called "decay products. Although thorium (90Th) has 6 naturally occurring isotopes, none of these isotopes are stable; however, one isotope, 232Th, is relatively stable, with a half-life of 1.405×1010 years, considerably longer than the age of the Earth, and even slightly longer than the generally accepted age of the universe. I think you should be able to pick up radioactivity of a lunar space suit after only 50 years, what do you think?