Antineutrino detection strengthened with new plastic scintillator

How can we find and measure nuclear particles, like antineutrinos, which travel at close to the speed of light?

Antineutrinos are the antimatter partner of a neutrino, one of nature’s most elusive and least understood subatomic particles. They are commonly seen near nuclear reactors, which emit large amounts of antineutrinos, but they are also found in abundance throughout the universe due to Earth’s natural radioactivity, with most of them originating from the decay of potassium 40, thorium 232 and uranium. -238 isotopes.

When an antineutrino collides with a proton, a positron and a neutron are produced, a process known as inverse beta decay (IBD). This event causes the ignition of scintillating materials, making it possible to detect these antineutrinos; and if they can be detected, they can be used to study the properties of a reactor core or the Earth’s interior.

Researchers at Lawrence Livermore National Laboratory (LLNL), in partnership with Eljen Technology, are working on a possible detection solution: a lithium-6 doped plastic scintillator to detect reactor antineutrinos, representing more than a decade of research in materials science. Their research appears in the journal Nuclear instruments and methods in physics research Section A: Accelerators, spectrometers, detectors and associated equipment.

Plastic magic

In the early 2010s, LLNL materials scientist Natalia Zaitseva and her team were the first to develop a plastic scintillator capable of pulse shape discrimination (PSD), i.e., effectively distinguishing neutrons gamma rays (important for detecting IBD events). Building on this work, the new formulation of lithium-6 doped plastic scintillator is also PSD compatible.

“Lithium-6 is particularly advantageous, because in addition to having a significant thermal neutron capture cross section, it provides a localized capture location, further enhancing the detector’s ability to effectively reject unwanted background noise,” he said. said LLNL scientist Viacheslav “Slava”. Li. This improved detection is made possible through the IBD process.

“While integrating lithium-6 into liquid scintillators has proven to be both a difficult and rewarding endeavor – successfully demonstrated by PROSPECT, another reactor-antineutrino experiment with fundamental contributions to LLNL – achieving this in a solid, compact and easily transportable plastic scintillator has not been achieved before, especially not on a scale suitable for efficient detection of antineutrinos,” said LLNL scientist and corresponding author Cristian Roca. the article.

Compared to liquid scintillators, which have been the standard technology for reactor-antineutrino detection for decades, plastic scintillators offer superior safety and mobility with fewer regulatory and practical constraints that are typically imposed on liquid scintillators and their environment. exploitation.

Optimizing detector performance

To prepare the scintillator (commercially known as EJ-299-50) for the market, researchers in LLNL’s Rare Event Detection Group conducted a series of measurements to characterize the material’s performance in a system of large-scale detection.

For nearly six months, the researchers studied the aging process of these scintillators to ensure the long-term stability of the plastic. After demonstrating the reliable optical performance and neutron identification capabilities of EJ-299-50 during this period, the researchers installed 36 of the plastic scintillator “bars” in a 6 × 6 grid configuration on a detection system called Reactor Operations Antineutrino Detection Surface Testbed Rover. (ROADSTR). A follow-up study is currently underway to evaluate the performance of ROADSTR with these bars.

Alongside their work on scintillators, scientists in the Rare Event Detection group are collaborating with researchers at the University of Hawaii to improve the directional sensitivity of the detectors; that is, the ability to determine the direction of the incoming antineutrino relative to the detector. This information can be extracted by correlating events occurring during the IBD response and is particularly useful in limiting illicit production of military equipment.

The team’s research, published in Applied physical examination and supported by the Monitoring, Technology and Verification Consortium, explores different detector designs, finding that some detector geometries outperform others in directional resolution.

With applications in the areas of reactor safeguards and monitoring, as well as homeland security and nuclear nonproliferation, these combined research efforts open the door to a new era of antineutrino detection.