Penn State researchers will participate in a new international multi-laboratory and multi-university collaboration led by Lawrence Livermore National Laboratory (LLNL) that harnesses the unusual characteristics of the elusive subatomic particles known as antineutrinos for nuclear nonproliferation–the prevention of the spread of nuclear weapons. The program will support the development of detection hardware and algorithms to improve nonproliferation detector capabilities for remote monitoring of nuclear reactors.
The initiative, known as the Advanced Instrumentation Testbed (AIT), is sponsored by the Department of Energy's National Nuclear Security Administration (NNSA). The AIT will be built and operated as part of an ongoing nonproliferation research collaboration between national laboratories and universities in the US and UK.
"Fission in nuclear reactors generates heat, which is used to pressurize or boil water to turn turbines for electricity generation," said LLNL physicist and AIT principal investigator Adam Bernstein. "Our goal is to harness a largely neglected aspect of the fission process for practical purposes. This very same fission process results in the emission of enormous numbers of highly penetrating particles known as antineutrinos. In our testbed, we will demonstrate the capability to detect the operations of nuclear reactors at significant distances, using antineutrino emissions.
"One of the key components of the testbed, the WATCHMAN antineutrino detector, will perform reactor monitoring at about 25 kilometers," said Bernstein. "This demonstration will lay the groundwork for larger detectors that would be required to monitor or discover small reactors at distances of up to several hundred kilometers." (WATCHMAN is an acronym for the WATer CHerenkov Monitor of ANtineutrinos.)
Carrying no electric charge and weighing more than one million times less than electrons, neutrinos and their antimatter counterparts, antineutrinos, interact only very weakly with normal matter. As a result, they can travel through enormous amounts of material, well over a light year (nine trillion kilometers) of solid lead, without slowing down or stopping. This means that it is impossible to prevent reactor antineutrino emission with shielding, and even a reactor buried deep underground can be detected.
"Since the Nobel-prize winning discovery by Clyde Cowan and Frederick Reines using a reactor source in the late 1950's, scientists have spent over 60 years exploring the curious properties of neutrinos," said the project's co-spokesman, professor Mark Vagins of the University of California, Irvine. "With WATCHMAN, we'll have a chance to show how these fascinating particles can be put to work for a very practical purpose."
In addition to monitoring reactors from longer distances, more powerful neutrino detectors could help provide researchers with more understanding about how the universe works. WATCHMAN, once commissioned, will become one of a small set of large antineutrino detectors worldwide that are capable of detecting antineutrino bursts from supernovae.
Subject to final approval by contributing stakeholders, including the mine authorities, the AIT will be constructed at the site of the Boulby Underground Laboratory, an existing United Kingdom government-funded deep underground science facility operating in a working potash, polyhalite and salt mine (Boulby Mine) located on the northeast coast of England.
The technical goal of WATCHMAN is to detect reactor antineutrinos, and thereby observe reactor operations at a significant distance from a nuclear reactor complex, using a large water-based detector. Doping the water with trace amounts of the rare earth metal gadolinium, a neutron capture agent, greatly enhances its sensitivity to antineutrinos, which generate neutrons by interacting with protons in the water.
The demonstration consists of observing reactor operations, including turn-on and turn-off of individual reactors at the Hartlepool two-core reactor complex, 25 kilometers distant from the mine, with a 3,500-ton detector. Monitoring of this type may be of use in present and future cooperative monitoring agreements and treaties in which the goal is to track or restrict the production of fissile materials that can be used in nuclear weapons.
Penn State personnel bring a wealth of experience in neutrino physics, underground detector construction, and fast electronics design to the WATCHMAN experiment. Doug Cowen, professor of physics and of astronomy and astrophysics, and Tyler Anderson, research professor of physics, collectively have decades of experience in the design and operation of sensitive detectors deployed in challenging and remote environments.
"Tyler and I are leading the effort to design the data acquisition electronics for WATCHMAN, with a particular focus on building a system with the flexibility and speed to handle the unique signature produced by reactor electron anti-neutrinos as well as the abrupt spike in neutrino interactions produced by a galactic supernova," Cowen said.
WATCHMAN will be the first demonstration of remote monitoring of individual reactor operations at a significant distance, using a scalable water-based technology. The AIT also will permit deployment of numerous advanced technologies that are relevant for remote reactor monitoring and detection, including water-based liquid scintillators, fast photo-sensors, light concentrators and others.
New methods for improving sensitivity also will be studied with the AIT, including directional suppression of backgrounds, advanced calibration techniques, and sophisticated algorithms and techniques for optimal extraction and utilization of the antineutrino signal.
Further, since neutrinos are emitted by the earth itself, detectors like WATCHMAN and its successors may permit the measurement of geo-antineutrinos.
"By measuring geo-antineutrinos, scientists may be able to learn about the total heat output of the earth, as well as study the composition of the earth's crust and mantle," Bernstein noted. "WATCHMAN, and more broadly the AIT, offer examples of the powerful synergy that can be gained when tools developed for basic science are applied in nonproliferation contexts."
"At long last, I get to reply with a resounding `yes!' to the inevitable question I get asked of whether or not anything useful can be done with neutrinos," said Cowen.
The AIT consortium consists of Lawrence Livermore, Lawrence Berkeley, and Brookhaven national laboratories, the United Kingdom's Atomic Weapons Establishment (AWE) and the United Kingdom's Science and Technology Facilities Council's Boulby Underground Laboratory; eight U.S. universities, the University of California (UC), Berkeley; UC Davis; UC Irvine; the University of Hawaii, Iowa State University; Penn State; the University of Pennsylvania; and the University of Michigan, as well as one British university, the University of Sheffield.
"It's a truly remarkable team," said Vagins, the academic cospokesman. "The depth and breadth of experience in both nonproliferation studies and neutrino physics is unmatched."
LLNL has helped to pioneer a successful, and now worldwide, effort to develop relatively small ton-scale antineutrino detectors for monitoring fissile inventories in reactors at roughly 25-meter distances from the reactor core. The new program is a logical extension of this work, representing a 1000-fold increase in distance compared to LLNL's previous deployments.