Radioactive copper can&#x27;t stay radioactive long. The longest-lived isotope is 64Cu, with a half life of 12 hours.<p>Mildly radioactive junk is not that rare. Stanford used to have a little fenced area near the toxic waste incinerator with stainless steel parts left over from accelerator experiments cooling off.  55Fe has a 2.7 year half life, so you let it cool off for a decade or so, then recycle.  The only protection was an chain-link fence, a radiation warning trefoil, and a street light.  One day somebody cut the fence and stole the stainless steel, prompting a search of scrapyards. But the metal was near the end of its storage period anyway, and wasn&#x27;t detectable as radioactive.