From Deep Space to Dirty Bombs; UNH Scientists Retask Telescope
By David Sims, Institute for the Study of Earth, Oceans, and Space
May 21, 2008
NASA's Compton Gamma Ray Observatory. Photo courtesy of NASA.
UNH astrophysicist James Ryan knows how to detect radioactive emissions across
the vast sweep of our galaxy.
So when he watched National Guardsmen struggle to track down a radioactive
source inside a building as they conducted a drill mocking a terrorist dirty-bomb
operation, the proverbial lightbulb-in-the-head lit up.
“If we can detect radioactive aluminum-26 on the other side of the galaxy
we can find other radioactive materials like cesium-137 or cobalt-60 inside
a building or on the other side of the street by the same method,” Ryan
Ryan was a member of the UNH research team that helped build and operate the
gamma-ray imaging COMPTEL telescope onboard the Compton Gamma Ray Observatory
(CGRO), a 1991-2000 NASA mission dedicated to observing the high-energy universe.
Knowing that the space telescope accurately pinpointed and made images of
faraway radioactive elements like aluminum-26, which is produced by dying stars
and emits gamma-rays, Ryan understood that the same basic technology could
be retasked for work a little closer to home – like detecting, for example,
radioactive medical waste obtained surreptitiously for use in making a dirty
He and colleagues at UNH’s Space Science Center dusted off two spare
detectors made for COMPTEL and created a telescope that could potentially be
loaded on a truck and used for homeland security work such as scanning shipping
containers or buildings for radioactive materials.
The key operational aspect of the telescope, known as GRETA, short for the
Gamma-ray Experimental Telescope Assembly, is that unlike other technologies
such as Geiger counters or spectrometers it can accurately determine the direction
from which a radioactive source is being emitted by creating an image.
Of the mock National Guard exercise Ryan notes that while soldiers did have
precision spectrometers that can identify the source material, the isotope,
and can determine if that material is natural or man-made, they are omni-directional
Says Ryan, “So they might detect the presence of cesium-137 but they
won’t know where it is unless they get right up close to it, they’d
have to fish around inside the building.” Which is not an ideal scenario
when the first responders have multiple issues to worry about like other potential
hazards from pipe bombs or biological agents, as was the case in the high-stress
Although more sophisticated technologies are currently under development,
Ryan notes that there will be both a time lag and a big price tag associated
with this while GRETA is a currently available technology that can get the
“Here’s an instrument that has the sensitivity necessary for the
job and it’s available now,” he says.
Earlier this week Ryan’s UNH colleague, project engineer Jason Legere,
presented information about GRETA and its abilities to the 2008 IEEE Conference
on Technologies for Homeland Security, which brought together more than 300
innovators to focus on novel and innovative technologies addressing pressing
national security problems.
“What I think impressed attendees the most about GRETA wasn’t
just its ability to locate and identify radioactive materials, but to do so
from a safe distance. This makes GRETA unique,” says Legere.