Apart from the risk to human health, there is concern that some radioactive sources could fall into terrorist hands and be used for radiological dispersal devices (RDDs), colloquially known as "dirty bombs." In 2005 alone, the IAEA tracked 103 confirmed incidents of illicit trafficking of nuclear and radioactive materials, the majority of which involved orphan radioactive sources.

IAEA's strategy for locating orphan sources in a country is based on lessons learned from more than 20 country orphan source search and secure missions. It incorporates such measures as using administrative paper searches and examining bankruptcy records, equipping and funding search efforts, and launching public information campaigns to elicit the public's help in identifying possible orphan sources.

Georgia is one of the countries where the IAEA has worked extensively to locate orphan sources. As many as 300 radioactive sources have been recovered in Georgia since the mid-1990s, a legacy of the region's sharp economic decline after the break-up of the Soviet Union.

In 2006, MacKenzie was part of a team that located a powerful source of cesium-137 in a pile of dirt in an abandoned factory. They also found a second smaller source in a box of nuts and bolts in a private home, just one thin wooden wall away from the family bedroom. Cesium-137 is a common radioactive isotope used by industries to check materials for flaws, and for making industrial measurements.

Scientists Expand Nuclear Rating Scale
Just as hurricanes are rated for severity, and earthquakes have their Richter scale, so the International Atomic Energy Agency (IAEA) communicates the safety significance of nuclear events with a consistent numerical protocol. Not widely known outside the nuclear community, the International Nuclear Event Scale (INES) is the mechanism used to classify and report events to the world at large. At this week's annual meeting of the Health Physics Society in Portland, Oregon, a scientist describes the scale and how it is being expanded to include new types of events.

Cynthia Jones, who is the US representative to the INES Advisory Committee and is also a senior technical advisor on nuclear security at the Nuclear Regulatory Commission (NRC), has reviewed the use of the scale, and will illustrate how it is used, such as in reporting nuclear events in the US.

She will also report that the scale is now being expanded to include events related to radioactive-material transportation and radiation exposure events. More than 60 countries have agreed to report nuclear events to the IAEA, most within 48 hours.

Here is what the designations mean: A scale 1 event is referred to as an anomaly; a rating of 2 is an incident (where, for example, the regulatory limit for a radiation worker has been exceeded); 3 is a serious incident; 4 corresponds to an accident with mainly local consequences; 5 an accident with wider consequences; 6 a serious accident; and 7, the highest rating, is for major accidents. On this scale, the Chernobyl accident (1986) is a 7, while the Three Mile Island accident (1979) receives a 5 rating.

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