Good quality materials aren’t in the same league of emissions as medical isotopes with shorter half-life. I am assuming use of gamma emitter 99mTc as the most common.
If you had Naval quality pu 239, then neutron emissions would be minimal, and the alphas easily shielded. If a non- government had to process their own materials, likely it would be contaminated by 240 and 238 and radiating strongly. A search using a neutron pulse generator would be seeking a like echo.
Encasing a weapon in a neutron absorber would reduce its signature. Placing it concealed along the keel of a ship would also reduce odds of detection.
What if Iran supplied the fissile material and the triggers?