The purpose of DU rounds is to increase the mass density, and thus penetration, of a given diameter round. DU can be hardened harder than most steels,, but at about 40% more mass per unit volume,.. you want maximum force behind minimum diameter. DU allows doing this. The radiation is not the purpose.
The radiation is just enough to be a health hazard to the user. Or if left in the body, to the the victim, but only YEARS later.
The actual risk level is just high enough the US Veteran's Administration is collecting exposure related data ... to figure out just how much a risk it really is... it's more dangeorus for heavy metal toxicity than for radiation risk.
Smith & Wesson: the original point and click interface...