[ RadSafe ] Article: Neutron science: Back on track?

[John Jacobus]

>From Nature 438, 730-731 (8 December 2005)

Neutron science: Back on track?
Karen Fox

(Karen Fox is a science writer based in Washington
DC.)

Top of pageAbstractNext June, a $1.4-billion
neutron-scattering facility will come online in the
United States. Karen Fox finds out whether this
machine really can breathe fresh life into the ageing
Tennessee lab that is its home.

Oak Ridge National Laboratory is more than 60 years
old and, until recently, it looked that way. Despite
its track record in nuclear research, the host of
wildlife that wanders on campus, and the pretty
sunsets over the rolling hills of eastern Tennessee,
it looked unlikely to entice the energetic people who
are the lifeblood of any great laboratory.

Salvation may be at hand. The Spallation Neutron
Source (SNS), the largest scientific facility to be
built in the United States for a decade, will become
operational at Oak Ridge by next June. The
$1.4-billion machine will generate neutron beams by
firing high-energy protons at liquid mercury. Hundreds
of visiting researchers are expected to descend on the
laboratory and use these beams to probe the structures
of molecules and crystals.

"What this brings to the table is the opportunity to
do an entirely new class of experiment," says Jack
Rush, who retired earlier this year as director of
neutron scattering at the National Institute of
Standards and Technology (NIST) in Gaithersburg,
Maryland.

Researchers around the world will be keen to assess
the popularity and capabilities of the new facility.
Once there would have been no question about the
usefulness of such a resource. But in the two decades
since the US Department of Energy (DOE) first planned
a neutron facility at Oak Ridge, the options available
for mapping molecular and crystalline structures have
widened. Facilities that use X-rays to probe these
structures, such as the Advanced Photon Source at
Argonne National Laboratory in Illinois, have become
vastly more powerful. Meanwhile, the number of
researchers who work with neutrons has declined as
several ageing neutron-source facilities have closed.

Despite this, Japan is building a research facility
similar to the SNS at Tokai, which will be ready in
2007. European plans for an even more advanced
spallation source hit political setbacks a couple of
years ago; their proponents are keen to revive them as
a way of preserving the continent's long-standing lead
in neutron science.

Building excitement
At Oak Ridge, the new neutron source is generating a
palpable buzz. The facility managers are aware that
many potential users of the technique have learned to
live without it. So to bring them to a site far from
the universities where they work will require
exceptional management and technical support.

"You can have a philosophy of 'if you build it, they
will come'," says Paul Butler, team leader for NIST's
small-angle neutron-scattering instrument. "But in my
experience that doesn't work. You have to do more."
Butler is on the SNS users group committee, formed
when construction began in 1999, to make sure the
neutron source goes that extra mile to meet
scientists' needs.

Oak Ridge managers know they face a challenge. They
anticipate that just a few hundred researchers will
use the facility during its first two years of
operation, while its neutron output slowly ramps up to
its full potential. But they expect this to build up
to 2,000 users a year by 2015, as researchers
currently accustomed to using advanced X-ray sources
begin to be converted to the subtler and sometimes
complementary charms of neutrons.

Supporters of the neutron source say that it does
things that other mapping tools can't do. X-rays
bounce off electrons, and so scatter much more
spectacularly from heavier elements that have many
electrons than from lighter ones, such as hydrogen,
which has only one. It has been estimated that, as a
result, the placement of about half of the hydrogen
atoms in published protein structures derived from
X-ray studies are not known. Neutrons interact
directly with nuclei, making lighter atoms easy to
identify.

Structured approach
Dean Myles, head of structural biology at Oak Ridge,
points out that another advantage of dealing with
nuclei, rather than electrons, is the ability to
distinguish between different isotopes of the same
element. This means that researchers can, for example,
use deuterium — a heavy isotope of hydrogen — as a
marker for the position of a particular atom in a
molecule or structure. "I liken it to a black cat in a
snow field," says Myles. Because neutron sources can
map structures over time, a molecule labelled with
deuterium could, for instance, be watched as it
wanders across the surface of a sample that mimics a
cell membrane. Oak Ridge is keen to teach its users
the chemical tricks necessary for such work, and the
lab is also growing bacteria in deuterium-rich media
so that they produce deuterated proteins.

Neutrons can also probe magnetic moments in solids and
phenomena such as high-temperature superconductivity.
Theories explaining superconductivity can be tested by
mapping the position and movement of oscillations of
the magnetic moment at a range of different atomic
energy levels, Rush says. And the SNS should be able
to collect these data some ten times more quickly than
existing neutron facilities, owing to its high neutron
flux.

This high flux level — up to 1017 neutrons per square
centimetre per second — will also allow users of the
facility to extract useful information from smaller
samples. This, says Rush, is a valuable capacity for
people studying things in short supply, such as
proteins or newly developed polymers.

The facility also incorporates specialized equipment
to cater for different research needs. One instrument
will place samples under extremely high pressure,
helping planetary scientists who want to model the
hydrogen-rich interior of Jupiter. Until now, it has
been a struggle to reach pressures above 25 kilobars
simply because of a lack of beam intensity at neutron
sources, says Richard Nelmes, who specializes in
high-pressure neutron science at ISIS, the British
neutron facility near Oxford, which is currently the
most powerful spallation source in the world.

For Oak Ridge — the largest of the DOE's civilian
laboratories — the new facility provides a badly
needed opportunity to regain scientific momentum.
"It's a little bit of an engine you get rolling," says
Jeff Wadsworth, Oak Ridge's director. "It generates an
optimism that feeds on itself."

Face lift
Oak Ridge was built in 1943 to produce uranium and
plutonium for the Manhattan Project, and a major new
facility hasn't been added since the high-flux isotope
reactor was built in 1966. "There was first-class
research and great people, but it looked like a
decrepit 1950s lab," says Thomas Mason, who joined the
SNS project at Oak Ridge in 1998, becoming the lab's
associate director three years later. "People weren't
working with state-of-the-art facilities."

Next year's opening is the culmination of a prolonged
struggle to rectify that. Back in 1984, a National
Academy of Sciences panel recommended the distribution
of various scientific facilities to different DOE
labs, with the largest one — a proposed advanced
neutron-source reactor — allocated to Oak Ridge. But
in 1995 Congress halted the $2.9-billion project just
before construction began.

The DOE decided to build a less expensive,
accelerator-based neutron source instead: the SNS.
Developed as a joint project between a number of the
department's laboratories, including Los Alamos in New
Mexico and Brookhaven in New York state, it was
decided to locate the facility at Oak Ridge, in the
home state of then-vice-president Al Gore.

After construction began, Oak Ridge's management
contract was taken over by the University of Tennessee
and Battelle, a contract research organization based
in Ohio. The new management team has been working hard
to secure extra investment for the lab: for instance,
it has borrowed $115 million from private banks to
build associated infrastructure, including a new
centre for computational sciences. On the back of
that, Oak Ridge has won leadership of a large DOE
supercomputing initiative.

"There is a substantial amount of risk that goes along
with the debt," says Wadsworth. "But we believed it
would help to attract more contracts and to grow our
business, and so far we've been successful."

Ultimately, Oak Ridge will measure its success by its
ability to attract world-quality researchers — both as
visitors and as staff. "You put enough bright people
together and interesting things happen," says Butler.
"There are all these buildings going up on the hill,
and then you put in these people and resources, and
add 1,500 users with all their new ideas." In these
gentle southern hills, he predicts, "it's going to be
a melting pot of ideas, bubbling away".

+++++++++++++++++++
"Efforts and courage are not enough without purpose and direction."
"John F. Kennedy, U.S. President and former Naval Officer 

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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