Victor L. Granatstein and Gregory S. Nusinovich at the University of Maryland, USA, have proposed a scheme for detecting a concealed source of radioactive material without searching shipping containers one by one.

The concept is based on the gamma-ray emission from the radioactive material that would pass through the container walls and ionize the surrounding air. The facilitated breakdown of the air in a focused beam of high-power, coherent, terahertz or infrared radiation would then be an indicator of the presence of the radioactive material. The gamma rays coming through the container walls could be detected by a pulsed electromagnetic source of duration between 10 ns to ms.

The team evaluated several candidate sources for this detection, including a 670-GHz gyrotron oscillator with 200-kW, 10-µs output pulses and a TEA CO₂ laser with 30-MW, 100-ns output pulses. A system based on the 670-GHz gyrotron would have enhanced sensitivity and a range exceeding 10 m.

However, at this early stage it is not yet clear whether this approach to detection of nuclear material is practical.

• Detecting excess ionizing radiation by electromagnetic breakdown of air,
  Victor L. Granatstein, Gregory S. Nusinovich,
  J. Appl. Phys. 2010.
  DOI: 10.1063/1.3484044