I would be negligent if I did not call attention to three important developments on the nuclear proliferation front.

First, the Ukrainian government claims to have arrested three of its citizens–including one local politician–who were trying to sell radioactive material.

The metal cylinder supposedly contained eight pounds of plutonium 239, a highly dangerous radioactive material that could be used in a nuclear weapon or a dirty bomb. The price: $10 million, sought by three Ukrainian men, officials said Tuesday.

The men did not make a sale, the officials said, but were arrested in an undercover operation in Ukraine last week that was conducted by the Ukrainian Security Service. Still, while the plot was foiled, it underscored longstanding concerns that unsecured radioactive material in the former Soviet Union might fall into the wrong hands.

Marina Ostapenko, a spokeswoman for the Ukrainian Security Service, said it had turned out that the radioactive material was not plutonium 239. A preliminary analysis indicated that the material was most likely americium, a much more common and less potent radioactive material, Ms. Ostapenko said in a telephone interview from Kiev, the Ukrainian capital.

She said americium could be deployed in a dirty bomb but not in a nuclear weapon.

An americum-based dirty bomb is actually a nothing to sneeze at:

Americium (Alpha Emitter)

If a typical americium source used in oil well surveying were blown up with one pound of TNT, people in a region roughly ten times the area of the initial bomb blast would require medical supervision and monitoring, as depicted in Figure 4. An area thirty times the size of the first area (a swath one kilometer long and covering twenty city blocks) would have to be evacuated within half an hour. After the initial passage of the cloud, most of the radioactive materials would settle to the ground. Of these materials, some would be forced back up into the air and inhaled, thus posing a long-term health hazard, as illustrated by Figure 5. A ten-block area contaminated in this way would have a cancer death probability of one-in-a-thousand. A region two kilometers long and covering sixty city blocks would be contaminated in excess of EPA safety guidelines. If the buildings in this area had to be demolished and rebuilt, the cost would exceed fifty billion dollars.

This episode underscores the continuing threat posed by “nuclear leakage,” particularly from the former Soviet Union. In many respects, leakage presents the most likely scenario for terrorist acquisition of WMD. Obama talked a great deal about strengthening various cooperative programs the US has in place to reduce leakage–programs that suffered from benign neglect under the Bush Administration–and it won’t be a moment too soon.

Second, the situation on the Korean peninsula seems to be headed from bad to worse. The conventional wisdom still holds that this is yet another of Pyongyang’s tirades in its eternal quest to extract greater concessions from the world. But the North Koreans have gone further than usual this time, and so experts are starting to worry that this is a more serious confrontation that those we’ve seen in the recent past.

Third, fears about Pakistan’s fate continue to mount. I suppose this isn’t really a “development,” but a way of saying that the prospects for the non-implosion of nuclear-armed state haven’t exactly improved of late, despite Islamabad’s strong denial of its own fragility.

This has been the latest installment in our occasional “we’re all doomed” series.