The impact of neutron science facilities—like those at Oak Ridge National Laboratory (ORNL) that generate cold neutrons for basic science and engineering studies—is fundamentally limited by the flux of the neutrons that they produce, where the flux is the number of neutrons moving through a fixed area per second. Spallation neutron sources, which generate neutrons by colliding protons with a heavy target, yield the highest flux of all such sources.
ORNL is now working on a Second Target Station (STS), which will allow for a significantly higher flux than the First Target Station (FTS), which is now in operation. The STS at ORNL’s Spallation Neutron Source (SNS) is expected to produce a neutron source that is the brightest in the world, having a significantly higher peak brightness compared to the FTS, where the reflectometry instruments already fall short of being able to handle the highest available flux by a factor of around 100.
One powerful class of neutron science instruments that are most limited by the increasing source flux is neutron reflectometry, which is essential to many investigations of interfaces in fundamental physics, materials science, and bioengineering. Just as light reflects off of certain surfaces, so do cold neutrons, which are neutrons that have been slowed down to travel at speeds of less than 1000 meters per second with wavelengths around 1 angstrom (10-10m).
If reflectometers or other instruments are not able to accommodate the brightness of the higher flux neutron sources through the ability to accurately handle high neutron count rates, then the impact of the upgrade to higher flux is wasted.
In response to this concern, Associate Department Head, Professor, and UCOR Fellow Jason Hayward was awarded a grant for $459,893 by the Office of Basic Energy Sciences within the Department of Energy (DOE) Office of Science for his research “Neutron Detector Development for High-rate Neutron Reflectometry at the Second Target Station of Oak Ridge National Laboratory.”
This research will address the engineering challenges required to accurately handle high neutron count rates for next generation reflectometers, which may also benefit other next generation neutron science instruments, including small angle neutron scattering, spectroscopy, diffraction, and imaging.
Specifically, Hayward will work with UT Research Scientist Xianfei Wen, who helped to write the proposal, to develop a scalable, 2-D positive-sensitive, pixelated scintillator-based neutron detector module with an exceptional count rate capability (i.e., 10 MHz/cm2) that is capable of correctly identifying cold neutrons, even during the prompt flashes of gamma rays associated with spallation. Hayward is a prior recipient of a DOE Science CAREER award, wherein his team was tasked to work on technologies that would improve the impact of the same neutron science facilities by increasing the position resolution of cold neutron imaging instruments.
“We are excited to again have the trust of the Office of Science on this occasion to develop next generation instrumentation that can handle the high brightness of the neutron source they have funded,” he said. “This will help us better enable our colleagues here and abroad to realize the full scientific and engineering impact of this investment.”
The benefits from a higher flux spallation neutron source coupled to capable measurement instrumentation include a vastly reduced measurement time, from hours or days to minutes or even seconds. The advances should make targeted beamlines available to more users, while enhancing the quality of the available data.