Cesium-137 has a half-life of thirty years, which means that two centuries later, they’ll still be glowing with 1 percent of their original radioactivity. Since the color of the light depends only on the decay energy, and not the amount of radiation, it will fade in brightness over time but keep the same blue color. And thus, we arrive at our answer: Centuries from now, deep in concrete vaults, the light from our most toxic waste will still be shining.
