Radioactivity is the FIRST thing they should have checked for.
"And, as everyone knows, Radiation can only affect you if you touch it!" Tom Servo; MST3K episode "Gamera".
Sorry, but you touched a raw nerve with me.
Unless they went running down that tunnel with radioacive elements loose in a bucket, and were smearing it on the walls, they will find no trace of radioactivity!
If a Nuke bomb suitcase-type came thru, it would be well shielded, and not exposed at all! If nuke materials for a "Dirty Bomb" came in...unless they did the unclean "Bucket" method I described above, again...no residue.
The ONLY way there might be SOME detectable evidence is if something of high-enough Gamma activity came thru with insuficcient shielding (which would mean the Islamazis/Mexicans/fill-in-the-blanks responsible will either be dead/dying or suffering from radiation exposure, and therefore traceable!), and remained in the tunnel for a length of time. Then there MIGHT be some disturbance to the soil/wood/concrete that lined the walls that MIGHT be detectable ...but those tests are long, involved, and complicated; and if the soil contained ANY inate trace radioactive compounds, the test would be rendered useless.
That is the reality.
Thanks for the education..........and the reality check.