Three University of Maryland researchers are developing a new laser technique that could allow for more remote detection of radioactive, nuclear material.
The researchers’ technique involves firing two laser beams — one of low intensity and one of high intensity — into the air around a potentially radioactive source. The low—intensity beam ionizes the negative ions in the air, or removes one of their electrons, resulting in an elevated level of electrons, said Joshua Isaacs, a graduate research assistant in the physics department who is developing the technique with Phillip Sprangle, a physics professor at this university and Chenlong Miao, a graduate research assistant in the electrical and computer engineering department.
The high-intensity beam is used to create a spark in the air, and the speed at which the spark is formed can be an indicator of surrounding levels of radiation, Isaacs said.
The goal of this research is to demonstrate a new concept for the remote detection of nuclear materials such as colbalt-60, a radioactive material that can be used in making dirty bombs, Sprangle said. The Defense Threat Reduction Agency is funding the research.
“We came up with a way to detect the radioactivity from farther away than the actual radiation penetrates,” Isaacs said.
A paper describing and analyzing this technique was published in Physics of Plasmas in March.
Traditionally, one would have to place a Geiger counter in the radiation’s vicinity to detect any radioactivity, Isaacs said. But this method is not always practical.
Radioactive material gives off ionizing radiation, causing neutral air molecules to be ionized and lose electrons, Isaacs said. Some of these electrons recombine with positive ions and neutralize them, he explained, but others attach to neutral molecules such as oxygen, forming negative ions.
The net result of this process is that, in the presence of radioactive materials, the level of ions in the air is elevated.
“Our concept is based on the detection of electromagnet signatures in the vicinity of nuclear material and can enable stand-off detection … [at a distance] greater than 100 meters,” Sprangle said.
The laser technique does have limitations, Isaacs said, such as the range of detection, which is limited to several hundred meters.
“It’s a less accurate detection, but more useful in certain circumstances,” Isaacs said. “It’s safer than getting close to the source of radioactive material, and it can scan a large, remote area very quickly.”
For example, there is no way to individually scan every single container on an approaching cargo ship, meaning most containers would go unchecked, Isaacs said. But a remote detection device utilizing this laser technique, either at port or mounted on a helicopter, could potentially check each container by tracking radioactivity in the surrounding air.
Isaacs, Miao and Sprangle’s method of remote radiation detection is “extremely promising,” said Howard Milchberg, a professor in the electrical and computer engineering department.
“We will soon be testing it out in my lab,” Milchberg said.
The research is still in development, Isaacs said, and the next step is laboratory experiments at this university. Eventually they hope to run field tests, though he said there is not a clear timeline for that stage just yet.
