The photo to the right shows the collection's display of cat litter. Notice the cat litter on the outside of the "box" and the dried raisins inside. It won't be long before the raisins are also on the outside. For fun, I measured the radionuclide activities in one sample of cat litter. The results were as follows: 4 picocuries per gram (pCi/g) for members of the uranium series, 3 pCi/g for members of the thorium series, and 8 pCi/g of potassium-40. At these concentrations the exposure rate at six inches above a box of cat litter would be approximately 0.1 micro roentgen per hour (uR/hr) above background. Since cats don't spend a lot of time in the litter box (you never see them taking along something to read when they are heading that way), the radiation exposure is probably minimal.