"exceeds ambient levels" wouldn't any additional radiation make that happen?,(reply>), amount of tolerable radiation is two or three orders of magnitude above what's "ambient" over most of the world. If the artifacts' radioactivity has lasted 100 years, then the level of radiation it produces is so low that its health effect is negligible. I've worked in undergraduate physics labs where we spent three hours multiple weeks in a row handling gamma sources with half-lives of around 5 years (Co-60), all with literally zero fancy safety precautions. With a half-life 320 times shorter than the radium isotope here, those sources put off roughly 320 times the amount of radiation in the same period. Additionally, radium is mostly an alpha source--most of the output is stopped by the skin. Radon is the real safety concern, but with a 1600yr half-life, a radium sample produces at most a few thousand atoms of radon in a day. My guess is the parks service closed the beach for PR reasons more than actual safety ones.,(reply>), I suppose that "ambient levels" is a range within the radioactivity is safe to be around, rather than the average level of background radiation in an area.,(reply>), As far as I know, ambient levels fall in a range, and often vary wildly by location. When radiation is "above ambient levels" it doesn't mean it's above average, it means that it's above the upper limit of what could be considered normal, mostly harmless background radiation.