Enhanced IPNS to train Spallation Neutron Source user community
by Jeff Evans
 Instruments crowd the experiment floor at the Intense Pulsed Neutron Source. |
After two decades of service to the scientific community, Argonne's Intense Pulsed Neutron Source (IPNS) is performing at its peak, and researchers are planning for an influx of new users and designing instruments for the next generation of neutron sources — the Spallation Neutron Source (SNS).
A pioneering national user facility, IPNS uses pulses of neutrons — uncharged, magnetic particles that form part of the nucleus of almost every atom — to probe the structures of materials ranging from semiconductors to proteins. Knowing the structure permits researchers to understand the physics controlling material behavior.
Since IPNS' first neutron pulse on Aug. 4, 1981, Argonne scientists have established the effectiveness of pulsed neutron sources, helped create the neutron user community and steered the direction of its research.
The first of its kind
IPNS was the first true user facility in the U.S. neutron source community, according to IPNS Division Director Raymond Teller and Jack Carpenter, IPNS' first director and its current technical director. Carpenter and other Argonne researchers built the IPNS predecessors — the first pulsed spallation source for neutron scattering, called ZING-P and ZING-P´ in the mid-1970s.
 Nicole Murphy assembles a new super-critical fluid extraction cell for pressure studies on the glass, liquid and amorphous diffractometer instrument at IPNS. |
"IPNS has devoted 75 percent of its beam time to outside users since its startup," remarked Teller. Outside users include researchers from industry, universities and other national laboratories across the world. Nuclear reactor-based neutron sources such as Brookhaven National Laboratory's High Flux Beam Reactor and Argonne's CP-5 Reactor, both now decommissioned, were user facilities, but they only devoted 5 to 10 percent of their time to outside users, Teller said.
"Now, when DOE builds a neutron user facility, they use the IPNS model," added Teller. "The fact that DOE is building the SNS is a real indication that IPNS got it right the first time."
The American Nuclear Society named IPNS a Nuclear Historic Landmark in 2002 for its essential contributions to nuclear technology.
Comparing IPNS and SNS
The $1.4 billion SNS is being built at Oak Ridge National Laboratory. Scheduled for completion in 2006, it will be the world's most intense spallation source for neutron scattering research.
The SNS will work much like the IPNS since both aim a pulsed beam of protons at a target, which, by a process called "spallation," emit pulses of neutrons that are trained on material samples.
But the SNS will operate at a higher energy of one billion electron volts, at beam intensities 40 to 100 times as strong and with liquid mercury as a target instead of the IPNS' depleted uranium.
At higher beam intensities, the SNS will allow scientists to examine the structure of small samples of substances, such as protein crystals, that are difficult to create in large amounts. Not only will a higher-intensity beam improve the resolution of a sample's atomic structure, but it will also make experiments run much faster — often an important factor as when following rapidly evolving changes in a sample.
"This means that an experiment that takes an hour to complete at IPNS could be done in less than a minute at SNS," said Teller.
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