The US Nuclear Regulatory Commission defines a dirty bomb as a “type of Radiological Dispersal Device (RDD) that combines conventional explosives, such as dynamite, with radioactive material.” Although most do not produce enough radiation to kill many people, an RDD explosion could engender a number of prolonged and unpredictable consequences, including mass hysteria, significant health risks – both physical and psychological – due to radiation exposure, property damage and economic repercussions, such as major cleanup costs.
While the first thought that may come to mind might be that of weapons-smuggling through customs or packages mailed throughout the postal system, most radioactive products passing through these facilities are benign medical or industrial products. Because the laws and regulations classifying them and governing their transport are somewhat complicated, especially internationally, they are invariably flagged and inspected typically for reasons of protocol. However, officials keep in mind that products and substances intended for innocent purposes can also be used for purposes that are not innocent.
For this reason, everything radioactive passing through many of the world’s main postal centers has to be checked.
One commonly found substance is Cesium-137, a soft, flexible, silvery-white metal that easily bonds with chlorides to create a crystalline powder. The U.S. EPA notes that “Exposure to Cs-137 can increase the risk for cancer because of the presence of high-energy gamma radiation. Internal exposure to Cs-137 through ingestion or inhalation allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, which increases cancer risk.”
Despite its danger, Cs-137 is used in small amounts for calibration of radiation-detection equipment, such as Geiger Mueller counters. In larger amounts, Cs-137 is used in medical radiation therapy devices for treating cancer; in industrial devices to measure the thickness of materials, such as paper and sheet metal, photographs, and other uses.
In addition to small quantities of such radioactive isotopes used in medicine and industry, inspectors are, indeed, also seeking to identify radioactive material that, in consolidation, could be used by terrorists to make a dirty bomb. Isotopes that can pose such a threat are known as Special Nuclear Material (SNM) and include Plutonium, Uranium, and Neptunium (Pu, U, Np). When these isotopes are detected, ‘red flags’ are raised. That’s why it’s critical to know the exact isotope of the radioactive material in order to assess the potential threat and quickly initiate a plan of action. There’s a big difference if the radiation detected is Cs-137 from medical equipment or Plutonium-239, which is used to make nuclear weapons.
With radioactive isotopes, the types of radionuclides and their quantity or concentration become the issue that requires detection and identification of all of them that may be passing through customs or a major international postal facility. A terrorist’s dirty bomb isn’t made from one small packet of an isotope intended for medical diagnostic instruments, but from a collection and concentration of certain classes of isotopes collected together in one place.
Fortunately, there are radiation detection and measurement technologies that can help mitigate the threat. Every isotope has its own signature ‘spectrum’ that can be detected and displayed on a handheld Radiation Isotope Identifier. Officers can quickly scan the suspected material with the instrument, which analyzes its acquired ID spectrum in real time, and automatically displays the optimum scan time to accurately detect the presence of Special Nuclear Material (SNM). These handheld instruments are capable of checking large bundles, pallets of products, or rooms full of goods for signs of unseen radioactive elements – and visually alert the operator to the presence of isotopes.
These detectors must be capable of not only determining that radiological material is present, but also what material it is. In this manner, then, an inspector can gauge whether or not the material is of low significance, or if the package needs to be opened and examined.
That identification goes a long way toward saving time and preventing wasted time and unnecessary alarm, and also of preventing the misdirection of fissionable material to malicious purposes.