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17 March 2002

Hand-Held Radiation Detector Could Prevent Nuclear Smuggling

(System could detect radioactive materials entering ports, airports)
Engineers at the Department of Energy's Lawrence Berkeley, Lawrence
Livermore, and Los Alamos National Laboratories have developed a
10-pound, battery-powered radiation detector called Cryo3 that is
intended to detect anyone trying to smuggle radioactive material into
the country.
Although technical problems remain, DOE researchers foresee a time
when reliable, portable radiation detectors could be operating at any
customs port or border station.
Following is the text of a Department of Energy science article:
(begin text)
Office of Science 
Department of Energy 
March 11, 2002
Hand-Held Radiation Detector Could Outsmart Terrorists
By Dan Krotz 
Science Writer 
Lawrence Berkeley National Laboratory
Long before September 11, engineers at Lawrence Berkeley National
Laboratory, in collaboration with researchers at Lawrence Livermore
and Los Alamos National Laboratories, have been working to outsmart
terrorists attempting to smuggle radioactive material into the
Their solution is Cryo3, a 10-pound, battery-powered detector that
promises to bring state-of-the-art radiation spectrometry anywhere
radioactive materials are found.
"The innovation is coupling a germanium radiation detector with a
small, low-power cryogenic cooling mechanism originally designed for
the aerospace industry," says Lorenzo Fabris of Berkeley Lab's
Engineering Division. "This offers extremely high-resolution radiation
analysis in a portable package."
The need for a hand-held radiation detector was first born from a
necessity to monitor nuclear weapon stockpiles to ensure nations
adhered to treaty obligations. An even more pressing need surfaced
after the dissolution of the Soviet Union, when national security
experts worried the former superpower's nuclear arsenal could spark a
black market in fissile materials. In the wrong hands, these isotopes
could be used to build both nuclear bombs and conventional bombs laden
with radioactive material-a so-called dirty bomb. And rather than
being delivered via intercontinental missiles, contraband isotopes can
be hidden in backpacks and car trunks, meaning airports, border
checkpoints, and shipping terminals provide the last best chance to
thwart smuggling.
To complicate matters, any tool used to screen for isotopes in busy
terminals must detect not only the presence of radiation, but also the
type. A terrorist could mask radioactive material destined for a dirty
bomb in a seemingly benign package of medical isotopes, and therefore
sneak past a Geiger counter.
That's where the Cryo3 comes in. At the heart of the unit is a high
purity germanium crystal. Energetic photons, X, and gamma rays,
interact in the germanium crystal to create a corresponding charge.
When further processed, this charge depicts both the quantity and type
of radioactive isotope present. Although germanium offers higher
radiation resolution than other semiconductor detectors, such as
silicon and cadmium telluride, it must be deeply cooled, traditionally
with liquid nitrogen. And although liquid nitrogen is very common in
the laboratory, it is awkward to transport, store, and handle in the
To sidestep this limitation, Berkeley Lab engineers coupled the
germanium crystal to an off-the-shelf mechanical cooling device
currently used to cool low-noise cell phone antennae. The device,
which utilizes the Sterling cycle to reach low temperatures, only
requires 15 watts to cool the germanium to 87 degrees Kelvin. When the
cryogenic mechanical cooler is vacuum sealed to a germanium detector,
the result is a lightweight, highly sensitive radiation detector that
operates up to six hours on two rechargeable camcorder batteries.
The mechanical cooler requires 16 hours to cool the detector from room
temperature to operating temperature, but because the batteries are
hot swappable, a fresh supply guarantees unlimited operational time.
To keep the system portable and low power without sacrificing
resolution, Fabris and colleagues made additional refinements.
Borrowing from lessons learned in satellite-based germanium detector
applications, they protected the delicate crystal in a hermetically
sealed, nitrogen-filled capsule. The encapsulated germanium detector
is suspended with Kevlar fibers in a close-fitting utility vacuum
Another obstacle was electronic noise, a byproduct of all electrical
systems that is particularly troublesome in radiation detectors
because it degrades the electronic readout's depiction of the absorbed
radiation. In short, electronic noise softens the readout's sharp
spikes into rounded hills, meaning valuable data is lost. Fabris
turned to a specially designed small, low-power preamplifier that
minimizes electronic noise without sapping battery power-a critical
component, given that conventional preamplifiers are too power-hungry
to be used in a battery-powered device.
So far, Fabris and colleagues have developed detectors of modest size,
or so-called 25 percent efficient detectors. In the future, they hope
to increase the detector size and therefore the efficiency to 50 and
even 100 percent by using modified mechanical coolers that only cool
to 105 degrees Kelvin, a temperature still within germanium's
operating parameters. The modified mechanical coolers have almost
twice the heat lift for the same input power when compared to the
conventional mechanical cooler.
Ultimately, Fabris foresees a time when next-generation iterations of
Cryo3 safeguard the nation with lab-quality, portable radiation
detection and characterization.
"Whatever you can detect with a germanium crystal, you can detect with
the portable system," says Fabris. "Ideally, we would be able to place
one at any customs port."
(end text)
(Distributed by the Office of International Information Programs, U.S.
Department of State. Web site:

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