come again.... Since when can uranium be held in your hands with no adverse effects?
U-235. Only when an atom of U-235 is split will it give off gamma radiation.
I wouldn't recommend trying to hold U-238 in your hand.
U235 only puts off a small amount of alpha radiation which is normally blocked by a piece of paper, an inch or so of air, or even the layer of dead skin cells you have on you. Just don't breathe in any U235 dust.
Radiological Health Risks of Uranium Isotopes and Decay Products In general, uranium-235 and uranium-234 pose a greater radiological health risk than uranium-238 because they have much shorter half-lives, decay more quickly, and are thus "more radioactive." Because all uranium isotopes are primarily alpha emitters, they are only hazardous if ingested or inhaled. However, because several of the radioactive uranium decay products are gamma emitters, workers in the vicinity of large quantities of uranium in storage or in a processing facility can also be exposed to low levels of external radiation. Chemical Toxicity Exposure to uranium can result in both chemical and radiological toxicity. The main chemical effect associated with exposure to uranium and its compounds is kidney toxicity. This toxicity can be caused by breathing air containing uranium dusts or by eating substances containing uranium, which then enters the bloodstream.
Depends on the isotope. U-232 is fine, 235 is ok. U-238. . . is another story. . . .