FRIB To Construct A Next-Generation Neutron Detector


Empowered by a National Science Foundation (NSF) grant, the Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) is spearheading a multi-institutional project to construct a next-generation fast-neutron detector unlike any other in the world. Researchers and students at eight U.S. colleges and universities—Virginia State University, Augustana College, James Madison University, Davidson College, Wabash College, Hope College, Indiana Wesleyan University, and MSU—are participating in this pioneering effort.

The MoNA-LISA neutron detector array is made of long scintillator bars that are read out by a pair of photosensors (photo multiplier tubes) at each end. MoNA (right) was constructed in 2003, and LISA (left) in 2011.

The project aims to build a modular plastic scintillator array for fast neutrons at FRIB. FRIB is a scientific user facility for the U.S. Department of Energy Office of Science (DOE-SC), supporting the mission of the DOE-SC Office of Nuclear Physics. User facility operation is supported by the DOE-SC Office of Nuclear Physics as one of 28 DOE-SC user facilities.

The detector will capitalize on FRIB’s mission to advance the field of nuclear physics by unlocking new scientific understanding of exotic nuclei and allowing undergraduate students to learn key technical skills and contribute to nuclear physics research. It is expected to be completed in 2026.

“This new fast-neutron detector will position us to explore distant regions of the nuclear landscape like never before, sharpen theories, and train a new generation of scientists in the process,” said Thomas Baumann, staff physicist at FRIB, who is leading the project.

Two decades in the making

In 2000, Baumann, then a postdoctoral researcher at the National Superconducting Cyclotron Laboratory (NSCL) at MSU—the predecessor to FRIB, led the design of a large-area neutron-detector array called the Modular Neutron Array (MoNA). MoNA was later complemented with the Large multi-Institutional Scintilator Array (LISA). Both detectors are the workforce of the MoNA Collaborationthat manages them. In addition to the eight institutions participating in the project, the MoNA Collaboration also includes Indiana University South Bend, Central Michigan University, Concordia College at Moorhead, and Argonne National Laboratory.

The concept of the next-generation neutron detector consists of scintillator tiles that are equipped with an array of light sensitive silicon photomultipliers (SiPMs). The image shows a simulation of the scintillation light that is detected by the SiPMs.

Researchers at FRIB and partner institutions used MoNA-LISA to conduct multiple experiments each year. MoNA-LISA explored the most neutron-rich nuclei that can exist in the universe and even unbound nuclei that decay right away, delivering insights on nuclides like neon-31, beryllium-16, and oxygen-26. It also contributed valuable learning experiences to more than 250 undergraduate students across a dozen institutions involved in the MoNA Collaboration headed by MSU.

While MoNA and LISA produced results and informed the development of other neutron detectors, Baumann remained convinced he could design a more precise instrument.

“At the time we built MoNA, I didn’t come up with an idea that was better than what was already available, so I basically built a detector that was simpler than what was available,” Baumann said.

The current design, however, aims to surpass today’s best-in-class detectors, including MoNA. NSF funding for the project—“Collaborative Research: Equipment: MRI Consortium: Track 2 Development of a Next Generation Fast Neutron Detector”—will help Baumann and his colleagues pursue that objective.

Novel design, novel results

Thomas Baumann

Baumann’s latest design concept jettisons the long plastic scintillator bar and prevailing time-difference method used in MoNA and other fast-neutron detectors around the world in favor of silicon photo multipliers (SiPMs). The novel instrument promises to improve the position resolution of the current MoNA and LISA detectors by a factor of five. Yet more, its unique tiled design will offer flexibility to specific experiment needs.

“With this detector, we can get more precise data and validate or tweak existing theories,” said Paul Gueye, associate professor of nuclear physics at FRIB and in MSU’s Department of Physics and Astronomy and a decade-long member of the MoNA Collaboration.

The new detector array will significantly boost the precision of nuclear structure measurements. This will enable scientists to better understand how protons and neutrons interact inside nuclei, generate fresh insights on heavier, more exotic isotopes, refine existing theories, and create a richer understanding of the universe.

“We can produce knowledge not present before, which is incredibly exciting,” Gueye said.

Fostering scientific talent

The NSF-funded project is also unique for its collaborative energy and focus on developing the pipeline of U.S. scientific and technical talent.

Directed by a MoNA researcher, undergraduate students at the eight participating institutions will each build 16 modular detectors. Those detectors will then be shipped to FRIB, where the Baumann-led team will compile a total of 128 detector tiles into one massive array.

Paul Gueye

“While this will be a cutting-edge device, the assembly and construction of it are still at the level that an undergraduate student can participate and be involved,” said Anthony Kuchera, an associate professor of physics at Davidson College. Kuchera has been a member of the MoNA collaboration since his days as a postdoctoral research associate at NSCL.

In FRIB, MSU—home to a top-ranked nuclear physics program nationally, according to U.S. News & World Report—hosts the only accelerator-based user facility on a university campus for students studying accelerator science, cryogenic engineering, and radiochemistry. DOE has identified developing nuclear scientists as vital to fueling the nation’s economic competitiveness, energy security, nuclear security, and nonproliferation efforts.

“Involving students in nuclear science has always been a focus of FRIB and the MoNA Collaboration and something we’re thrilled to be continuing with this new project,” Baumann said. “We believe it not only benefits the individuals themselves, but also contributes to science as a whole.”

The road ahead

Anthony Kuchera

Last year, Baumann distributed test kits to his partners. Students have been connecting photo sensors to plastic scintillators, soldering the sensors to circuit boards, and making early measurements with radioactive sources. Student-led computer simulations will assess various performance and geometrical aspects of the design. In addition, the test kit work will inform the construction of modular detector prototypes and contribute to the FRIB detector’s final design.

Baumann said the project’s goal is to include the detector in FRIB experiments within the next three years. Thereafter, it can serve the facility’s broader scientific user community and propel discovery in the field of nuclear science.

“The fundamental measurements possible with this new detector will allow nuclear scientists to test their understanding of scientific theories and models of the nucleus and drive knowledge in new directions,” Baumann said.

This story was first published by FRIB MSU.

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