Alarming uranium facts

I read a frightening article in the latest Scientific American today. "Detecting Nuclear Smuggling" highlights not only the difficulty of detecting nuclear materials, such as highly enriched uranium (HEU), in the 42 million shipping containers arriving at U.S. ports each year, but also this bombshell:

The "quality" of nuclear material since then [1945] has continued to improve.... Our modeling showed that, for an explosive-gun assembly, the minimum quantity that was required to obtain a one-kiloton explosive yield would be subtantially less than the amount of HEU in Little Boy [the atomic bomb dropped on Hiroshima]. Most disturbingly, with larger quantities, a one-kiloton yield could be achieved with a probability greater than 50 percent by dropping a single piece of HEU onto another.... Designing an HEU bomb seems shockingly simple.

Given the low probability of detecting HEU--when shielded it emits less radioactivity than is normally present in background radiation--the Scientific American article's authors recommend tackling the problem at the source. Obama has highlighted the need to do more in securing nuclear materials worldwide and passed legislation last year to aid in doing so.