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18 May 2019 _ PopularMechanics.com
HOW YOUR WORLD WORKS
HE TRAIN RIDE was as uneventful as the dozens of oth-
ers the man had taken from Washington, D.C., to New
York City. He watched the scenery change as he headed
north past Baltimore, along the Delaware River to Phil-
adelphia, through Newark, then into the long dark
tunnel on the final approach to New York’s Pennsyl-
vania Station. Throughout the trip, the device in his
pocket—the size of a portable hard drive, all black, with a sin-
gle button on the center of one side and a blinking blue LED light
above it—remained silent.
After getting off the train, the man moved with the large mid-
day crowd toward the entrance to the subway. On the uptown
platform, standing near a dark-haired woman in her late 40s,
he felt his pocket vibrate insistently. He
looked at his phone: high levels of gamma
rays. Technetium-99m. He was the only
one who knew.
The man, Vincent Tang, is a prominent
physicist at DARPA. He and his team have
spent the last five years working on Sigma,
a program for counteracting nuclear ter-
rorism. A year ago they launched Sigma+,
an expanded system that will identify
chemical, biological, and nuclear compo-
nents, along with explosives, to help law
enforcement stop terrorists before they
can strike. The major breakthrough is
the radioisotope identification device in
Tang’s pocket, the D3S, which was built
by the British company Kromek. Unlike
earlier versions, which were much larger,
the D3S fits in your pocket. And at a frac-
tion of the prev ious price, it can be carried
by every police officer, firefighter, EMT,
and other emergency-service personnel in a city. When paired
with a network of larger, more sensitive devices, both mobile
and at fixed points around a city, this creates a crowdsourced
dragnet for thwarting possible biological, chemical, explosive,
or nuclear attack.
The Sigma system is already being tested in a few major urban
centers across the United States. (They can’t be named for secu-
rity reasons.) Someday soon, Tang hopes, Sigma+ will be the
strongest tool available to cities in the fight against terrorism.
Despite the vibrating in his pocket, Tang isn’t concerned by
the reading on the subway platform. Technetium is the most com-
monly used radioactive tracer, an element doctors give patients
before X-rays and other hospital tests. But if it had been an ele-
ment used for a dirty bomb, Tang would have known just as quickly.IN A POPULAR MECHANICS EXCLUSIVE, Tang allowed us to test
the device in New York City for two weeks. But first he had to show
me how it works.
With special tracking software installed on my laptop, Tang dem-
onstrated how simple it was to follow the D3S in real time. Once it
was paired with his phone, as easily as you would add any Bluetooth
device, the D3S popped up on the map. Had we added more—say, an
entire police unit fanned across its precinct—we could have followed
them as well and got ten instant notifications
of any detected threats.
Next, the test. Inside the D3S is a one-inch
cube of thallium-activated cesium iodide
crystal. When the characteristic energy of
an isotope hits that crystal, it is absorbed
and re-emitted as light particles, which are
converted into an electrical signal that the
D3S reads.
Tang carefully set a palm-size lead con-
tainer (called a pig) on my kitchen table.
Inside were test samples of cobalt-60,
cesium-137, and radium-226, elements that,
in larger concentrations, could be fatal. He
took each out, and we watched as, within one
or two seconds, his phone vibrated with an
alert—an instant identification of the sub-
stance and the approximate amount.
After a little more instruction, I was on
my own. In two weeks of very determined
testing—and many miles of walking with
optimistic suspicion—I’m pleased (but somehow also slightly dis-
appointed) to have found nothing. There was a brief moment of
excitement when I passed the foreign embassy of a not-so-friendly
country and felt a warning vibration in my pocket. This was it! I
thought. I’m about to save the world! But then I looked at my phone:
fluorine-18, another isotope regularly used in medical testing.
With older equipment, that false positive, along with the one
Tang had on the subway platform, could have sent counterterror-
ist teams scurrying. New York City wasn’t any safer because of me,
but it will be when Sigma+ makes its way to our streets.Tiny Device Can Detect
Nuclear Armageddon
A new sensor—small enough to fit in pockets and cheap enough to fit in budgets—will
help law enforcement locate dangerous materials before terrorists can use them.
/ B Y D A N I E L D U B N O /