I was at an event this morning where Michael Swaine raised the question of identifying North Korean uranium in the event that it were used in an attack by another state or terrorist organization.

This subject has come up a fair amount lately, it seems. Yesterday, both “David Ignatius”:http://www.washingtonpost.com/wp-dyn/content/article/2006/10/10/AR2006101001282.html and “William Perry”:http://www.washingtonpost.com/wp-dyn/content/article/2006/10/10/AR2006101001285.html mentioned it in the _WP_. Perry wrote:

… the greatest danger to the United States from this program is not that North Korea would be willing to commit suicide by firing a missile at the United States, even if it did develop one of sufficient range. Rather, it is the possibility that the North Koreans will sell one of the bombs or some of their plutonium to a terrorist group…If a warning is to have a chance of influencing North Korea’s behavior it has to be much more specific. It would have to promise retaliation against North Korea if a terrorist detonated a nuclear bomb in one of our cities. It must be backed by a meaningful forensics program that can identify the source of a nuclear bomb.

Personally, I am less worried that North Korea actually will transfer a nuclear weapon or fissile material, though I wouldn’t rule it out entirely.

Anyway, I thought I’d take this opportunity to flog a “new _ACT_ article”:http://www.armscontrol.org/act/2006_10/CVRForensics.asp from William Dunlop and Harold Smith called “Who Did It? Using International Forensics to Detect and Deter Nuclear Terrorism.”

The piece includes a useful “sidebar”:http://www.armscontrol.org/act/2006_10/CVRForensics.asp#Sidebar1 about nuclear forensics. Here are excerpts:

In the event of a nuclear explosion, radiochemists would seek to obtain minute quantities of debris from the nuclear device near ground zero and/or in the atmosphere. They would first separate the atoms into groups of chemically similar elements and then measure the radioactivity of each group. To do so, scientists often employ gamma-ray spectroscopy to measure the time of emission and the energy of each detectable gamma ray, electromagnetic radiation produced by radioactive decay.

The energy of the detected gamma ray is unique to each isotope of a specific element, thereby indicating its presence in the debris. Furthermore, the rate at which that isotope emits its signature gamma ray decays in time according to its unique half-life, thereby providing a second identifier of the isotope. By knowing the chemistry of elements that have been separated, the energy of the gamma rays of any radioactive atoms in that chemical group, and the rate at which the emission of the gamma rays at each particular energy level decays over time, scientists can obtain an accurate measurement of many of the isotopes of the chemical elements in the debris. Because there is always experimental uncertainty, particularly with small samples, all three processes (separation, energy measurement, and time dependence) may be used.

According to the authors “[t]hree types of atoms are of particular interest in a forensic analysis:”

* Atoms of fissile material that did not undergo fission. Examining them allows scientists to identify the material used to make the device and, when compared to the number of fission fragments, to measure the efficiency or sophistication of the weapon.

* New atoms created by fission and by other nuclear reactions within the fissile material. When scientists compare these, they can obtain considerable insight into the nuclear processes that were involved during the actual explosion.

* Atoms of material near the fissioning core that were subjected to an intense bombardment of neutrons during the explosion and became radioactive as a consequence. These atoms provide insight into the components of the weapon and the energy of the neutrons that activated the components.

Back to work, nerds. My break is over too…