Suitcase-sized nuclear bombs?

Factual Questions
1

At some point in the wall-to-wall news coverage since the 9/11 tragedy, (NBC, Sunday morning maybe?) it was mentioned that it was known to American intelligence that Osama Bin Laden had tried twice in recent years to buy “suitcase-sized nuclear bombs”. He was apparently unsuccesful, although they didn’t go into details, at least not while I was watching. This raised, for me, a couple of questions:

  1. Nuclear bombs? The size of a suitcase?
  2. Would this be an unusually heavy suitcase?
  3. Are these things entirely self-contained; is everything one would need to get one of these things to go off inside?
  4. I’m guessing that such items might have ended up on the black market after the breakup of the former Soviet Union, require a fairly sophisticated infrastructure to make, and that they are not the kind of thing one can make in one’s garage, or some camp in the mountains of Afghanistan. True?
  5. Is there an estimate of how many of these things exist that are unaccounted for?
  6. Is there a serious international effort to track these things down and get them under the control of institutions that are not likely to let them go to the highest bidder?
  7. As a point of reference to current news stories, how much greater would the devastation have been if one of these objects had been detonated, say, at the base of one of the WTC towers instead of airplanes crashing into it?
2

This has been discussed at length in several previous threads. Here’s a good one:

http://boards.straightdope.com/sdmb/showthread.php?threadid=44233

3

Thanks for the link, Chuck. I did a search before posting but didn’t look back that far. The answers to some of my questions are there, or contained in links within. One of the posts, and one of the links, mentions that weapons of that size could take out the Kremlin or Capitol Hill, but not a city. To me, this doesn’t sound like much more devastation than was wrought at the WTC…not orders of magnitude more, anyway. They apparently weigh about 150 pounds, and no one is sure how many there might be unaccounted for. One person claims that below a certain point, small nuclear weapons become less cost-effective than “conventional” weapons.