![]() Bowden states, “The oscillation signature is the key to understanding the differences between prediction and observation. For electron antineutrinos from a nuclear reactor, the baseline at which oscillation first becomes noticeable is at about a 1-kilometer distance from the reactor. Each flavor state generates a unique oscillation signature, represented by a variation in the neutrino detection rate with the distance traveled (the baseline). As the neutrino travels away from its point of creation, the differing mass of those underlying states causes oscillation-wherein the neutrino transforms from one flavor to another. When a neutrino is created, it starts in a quantum superposition of three underlying mass states that represent the three flavors. PROSPECT probes this anomaly by searching for a particular signature: neutrino oscillation. In recent years, experiments at nuclear reactors have detected fewer antineutrinos than predicted, leading physicists to hypothesize that the missing particles were transforming into unobservable sterile neutrinos as they traveled. In other words, Mendenhall explains, “The positron carries away the antineutrino’s incoming energy, which allows us to measure that quantity.” PROSPECT measures the time delay between the proton–antineutrino collision and subsequent capture of the neutron, thus identifying IBD events. Successful neutrino detection at a nuclear reactor hinges on exploiting the inverse beta decay (IBD) process, in which the neutrino’s antiparticle-the antineutrino-collides with a proton, leaving behind a positron and a neutron. Neutrinos are electrically neutral, have a smaller mass than other elementary particles, and usually pass through matter undetected. (See S&TR, December 2012, Positively Scintillating Neutral Particles Brighten Scientific Prospects and July/August 2016, A Detector to Study the Neutrino's Nature.) Just when the elementary particle’s three “flavors” (electron, muon, and tau) were finally understood, along came the possibility of a fourth-the sterile neutrino-whose existence would pose new questions about the Standard Model of physics. Since its discovery 60 years ago, the neutrino has continually intrigued the physics community. PROSPECT is also the first full-scale detector operating aboveground, which opens up possibilities for mobile reactor monitoring technology.” Additional funding comes from Livermore’s Laboratory Directed Research and Development Program, the Heising–Simons Foundation, and other partners. In 2016, the PROSPECT team won the Department of Energy’s Office of Science funding competition for neutrino research projects that were, among other criteria, “modest in cost and timescale.” Bowden, who serves as the project’s co-spokesperson, says, “Many researchers are excited about small experiments in neutrino detection, and our collaboration is at the forefront with the first published results. (Photo courtesy of the PROSPECT collaboration.)Ĭompared to other detectors, which can weigh up to 50,000 tons, the 4-ton PROSPECT detector is more moderate in size. Livermore physicist Michael Mendenhall (left) and PROSPECT colleagues assemble components of the segmented detector array during its construction at Yale University. ![]() The PROSPECT detector began collecting data in 2018. Over the last six years, the detector was designed, then assembled at Yale University, and later installed at Oak Ridge’s High Flux Isotope Reactor (HFIR)-a user facility that provides a high-intensity neutron source for materials science and isotope production experiments. The PROSPECT collaboration began in 2013, and includes Livermore physicists Nathaniel Bowden, Jason Brodsky, Tim Classen, and Michael Mendenhall, as well as colleagues from the National Institute of Standards and Technology (NIST), Brookhaven and Oak Ridge national laboratories, and 10 universities. PROSPECT, the Precision Oscillation and Spectrum Experiment, is a unique neutrino–antineutrino detection project aimed at investigating fundamental particle physics and improving detection sensitivity for nuclear fission reactions. Perhaps the most exciting experiments are those that undertake both objectives. Others are intended to test-drive new mission-critical technologies. Many experiments conducted by Lawrence Livermore researchers are designed to explore questions of fundamental science. The Little Neutrino Experiment That Could The sophisticated neutrino–antineutrino detection system-the first aboveground detector of its kind-is sited at Oak Ridge National Laboratory’s High Flux Isotope Reactor (HFIR). Lawrence Livermore is a founding member of PROSPECT, the Precision Oscillation and Spectrum Experiment.
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