EVENTS, ADVANCES, AND NEWS
■ BY JEFF ECKERT
NEW CAMERA DETECTS
liquid scintillators in two planes. Neutrons traveling through the scintillators
bounce off the protons, energizing
them and creating the
“scatter.” When a proton
subsequently loses its
energy, it gives off light.
Using interactions in the
two planes, the camera
can ascertain the direction
and energy level of the
The biggest drawbacks
to this approach are
size (hand-held detectors
are considerably more
convenient) and the fact
that the scintillator material
is flammable and otherwise
hazardous to your health.
But solid scintillators could eventually
eliminate the latter problem.
After further development, the
Domestic Nuclear Detection Office
plans to ship the camera to Hawaii,
where the agency will study its
viability for shipboard operation.
PHOTO BY RANDY WONG.
■ Physicist Nick Mascarenhas prepares
the neutron scatter camera for a test.
Since 9/11, gamma-ray and
neutron detectors have been
deployed in many airports and border
crossings to help prevent nuclear
weapons or radioactive materials from
being smuggled into the country.
These instruments, however, have
some significant limitations in terms of
range and shield-penetration capability. A recent development at Sandia PHOTO COURTESY OF IBM.
National Labs ( www.sandia.gov),
however, promises to detect radiation over much greater distances
and through more shielding than is
possible with current apparatus.
The “neutron scatter camera” is
an improvement over traditional
neutron detection in that it “sees”
only high-energy neutrons and
ignores the uninteresting, low-energy ones that are all around us.
In a test, it also easily detected and
imaged a radiation source from across
a hallway and through several walls
Basically, the camera consists
of elements that contain proton-rich
10 February 2008
IBM CLOSER TO
COMPUTING WITH LIGHT
■ Diagram of IBM’s optical modulator.
For years, designers have talked
about the possibility of computing
with light pulses rather than electrical
signals. It now looks like scientists at
IBM ( www.ibm.com) have taken a
major step toward achieving it. The
breakthrough is a device, called a
silicon Mach-Zehnder electro-optic
modulator, that converts electrical
signals into light pulses. This, in itself,
is not particularly amazing. However,
the IBM version is said to be 100 to
1,000 times smaller than any such
devices previously demonstrated, so
it could eventually allow complete
optical routing networks to be placed
on a single chip, eliminating miles of
In operation, the device first
converts an electrical signal into a
laser beam and applies it to the
modulator. It uses tiny “silicon
nanophotonic waveguides” to control
the light flow on the chip, thus acting
like an extremely high-speed shutter.
Electrical charges injected into
the waveguide change the optical
properties of the silicon, thus
modulating the beam and creating
optical ones and zeros.
According to Dr. T. C. Chen, VP of
Science and Technology at IBM
Research, “Work is underway within
IBM and in the industry to pack many
more computing cores on a single chip,
but today’s on-chip communications
technology would overheat and be
far too slow to handle that increase
in workload. What we have done is a
significant step toward building a vastly smaller and more power-efficient
way to connect those cores, in a way
that nobody has done before.”
To put this into perspective, the
chip that powers the Sony Playstation
3 has nine cores on one chip. The
new technology could allow hundreds
or even thousands of cores to be
connected in the same space and
transfer data among the cores 100
times faster. Using this technology, a
supercomputer could someday fit into
a standard laptop case.