By Ernie Tretkoff
Ways in which physics can contribute to homeland security were discussed at the joint APS-AAPT spring New England section meeting, held April 4-5 at the Coast Guard Academy in New London, CT.
Alessandro Curioni of Yale said that some of the same gamma-ray detection technology being developed for astronomy could be used for homeland security. For security purposes, one might want to measure energy, direction, time and polarization of gamma rays. “The same problem is encountered in medical applications, biology, materials science and nonproliferation, and security,” said Curioni. Many current gamma ray detectors for homeland security typically just count gamma rays, but don’t measure their energy, so it can be difficult to distinguish harmless radioactive materials from dangerous ones.
One difficulty in detecting gamma rays for any purpose is that “there is no good focusing optics for gamma rays” Curioni said. Gamma rays are highly penetrating, and easily travel several centimeters through dense materials. A detector needs to have large area, large field of view, and large stopping power.
There are several types of interactions gamma rays produce when they hit a material, the most common being Compton scattering, in which a photon transfers some of its energy to an electron. The incoming gamma ray scatters in some detector medium, such as liquid xenon or liquid argon, and both the electron and photon are detected, giving a measurement of the energy of the gamma ray photon, as well as some information about the direction it came from. Compton telescopes are currently some of the most sensitive instruments to detect gamma rays for astronomical uses. Curioni and others are working on building better Compton telescopes. The energy resolution of these instruments is already good, though they could use improved position resolution, Curioni said.
Applying some of these developments to homeland security is the next step. “There is a lot of overlap between fundamental research in particle and astrophysics and applications,” Curioni said.
Joseph Schumer of the Naval Research Laboratory talked about ways to monitor cargo for dangerous materials. This is challenging because authorities would want to detect dangerous materials quickly, from far away, and without interrupting commerce.
For radiation safety, time, distance and shielding are friends, Schumer said. “These same things make it hard to find smuggled nuclear materials,” he said. Passive detection schemes, which simply detect radiation a material emits, are limited because radioactive materials can easily be shielded by those wishing to conceal them. Current scanners also have trouble distinguishing dangerous materials such as highly enriched uranium from harmless radioactive materials.
Active detection methods, which Schumer and others are working on developing, might work better. Such methods would hit the target container to be scanned with a beam of neutrons, which would induce fission in any fissionable material in the container, resulting in emission of a characteristic radiation that could be detected. This method could detect highly enriched uranium even through light shielding. Schumer called the scheme a “nuclear carwash.”
John Luginsland of NumerEX Corporation talked about simulations of directed energy devices. These devices, some of which are still at the science fiction stage, could be used to temporarily or permanently disable electronics without harming humans. A different type of directed energy device could be used for non-lethal crowd control, by creating a painful, though supposedly harmless, burning sensation. Directed energy devices could be non-lethal, could be deployed rapidly, and have selectable effects, Luginsland pointed out. However, the technology is immature and controversial.
Currently Luginsland and others are working on simulations of compact high power microwave devices. Such devices would use relativistic magnetrons, similar to the magnetron in a microwave oven, but much more powerful. Luginsland’s simulations, which start from the basic electrodynamics, can suggest ways to improve the devices. Applications require new, compact, high efficiency sources of electromagnetic radiation. Advanced computation is providing new ways to virtually prototype these devices, he said.
Tim Dasey of MIT Lincoln Lab focused on biological and chemical defense. Attacks with biological or chemical weapons such as anthrax would be extremely difficult to prevent, since it’s relatively easy for anyone to get hold of the materials and the knowledge to make a biological or chemical weapon. Dasey’s talk focused on what could be done in the aftermath of an attack. “The first thing you want to do is understand what happened,” he said.
That requires fast, reliable detectors. With most current detectors, “I can tell there’s a cloud of stuff somewhere, but I can’t tell if it’s biological, and certainly can’t tell if it’s anthrax,” says Dasey.
A basic detection system might have as a first level a trigger detector that would provide some tentative warning of a threat, and perhaps some rudimentary agent classification, but not specific details. Dasey’s group is working on making small and inexpensive biological agent warning systems that use ultraviolet laser light to induce fluorescence in amino acids that might be present. The next level of sensing would identify specific agents. There are several potential ways to do this. In one test device, the researchers took living cells and engineered them to respond to certain pathogens that they want to detect. When the pathogen hits the cell, a biochemical reaction in the cell releases calcium ions that could be detected. This method gives results in minutes, but the cells only live for about a week at room temperature.
After attack, there are several steps before action can be taken, including figuring out where exactly the attack originated, how large the attack was, who was exposed, and what medical response is needed. Time is crucial in such situations. Cities are developing response plans, and Lincoln Labs is developing simulation-based training tools to help, Dasey said. The researchers are also working on developing self-decontaminating surfaces and a wide variety of other tools to plan for many contingencies.
Even high school students can begin to learn the science involved in homeland security. Lea Beaulieu, a teacher at Joppatowne High School in Maryland, described a new program for high school students in homeland security and emergency preparedness. The program, developed in cooperation with partners in government, higher education, and industry, supplements the standard high school curriculum and is aimed at average students. Some students in the program choose a science track, in which they focus specifically on the science involved in homeland security, learning, for instance, the chemistry and physics involved in detecting dangerous materials and the biology of how the body responds to toxins. They have hands-on lessons using relevant technology such as Geographic Information Systems and chemical detectors. The program began last year, with about 60 tenth grade students. After graduation, the students may go on to college or directly into the job market. “Homeland security is a booming industry,” she said. Beaulieu also believes the program will help interest some students in science by showing them important ways science is useful.