[Mariner]

In fact, state of the art detection for "clean", weapons-grade PU239 (assuming 6% contamination of PU240) is a couple of miles, at best. And that's unshielded. Add an inch of lead and you're not likely to detect it next door.

Sailors sleep within a few feet of W-88 warheads without harm.

Yes, a Uranium bomb can be "seen" from at least 100 miles. But, for shielded Plutonium, it's virtually undetectable.

http://www.berthold.com/downloadfiles/rp/en_ieee_tns99_lb6414.pdf

[Scutter]

Yes, but that’s a passive detector. What if you have an “active” detector? IOW, one that scans an incoming vessel with neutrons and looks for the burst of gamma rays that come back from fissile material when hit with the neutrons.

[bvw]

Tks.