When SAMMY met VENUS: A powerful pairing introduces new method of non-destructive testing

At the Department of Energy's Oak Ridge National Laboratory, researchers have made a match in pairing the nuclear analysis code SAMMY with the high-resolution neutron transmission measurements from ORNL's Versatile Neutron Imaging Instrument (VENUS) to identify and verify nuclear materials.

Combined, these technologies offer a new approach for non-destructive assay (NDA) testing, a method of characterizing nuclear materials without dismantling or destroying a potentially hazardous sample.

"It's a perfect match, not just between two technologies, SAMMY and VENUS, but between the people and capabilities here at ORNL," said Luiz Leal, the report's lead author and a distinguished R&D staff member in the Nuclear Data Group at ORNL. "By teaming up the right partners, we've identified a new mechanism for NDA testing with applications across nuclear science and national security."

Meet SAMMY, a leading nuclear analysis code

Nuclear data underpins all of nuclear science, serving as an essential reference for starting nuclear reactors, modeling new nuclear systems and analyzing materials. Contained in evaluated data libraries overseen by research institutions and nongovernmental entities around the world, nuclear data encompasses detailed individual measurements about thousands of nuclear isotopes, such as decay constants and fission yields.

Nuclear analysis codes like SAMMY enable nuclear engineers and developers to use this data to inform models and simulations that can accurately predict nuclear system performance.

"ORNL has a long history of measuring and evaluating nuclear data," Leal said. "SAMMY has been a key tool for reconciling nuclear theory with actual measurements for nearly three decades. Ever since it was developed at ORNL, it's been a leading contributor of nuclear resonance data."

Finding the right fit in neutron cross section data

Nuclear resonances are derived from one of the most significant nuclear data points: the neutron cross section. A cross section represents probability that a neutron will interact with a specific nucleus and cause a nuclear reaction. Each isotope has a distinct cross section profile that allows it to be easily identified.

"Cross sections are almost like a fingerprint," said Leal. "They can be identified by developing a resonance signature, which is generated by directing a neutron beam at a sample material over a range of energies. Tools like VENUS can develop this signature through neutron transmission."

While these "fingerprints" are visually represented in curves on a graph, they are numerically represented in data libraries as resonance parameters. Resonance parameters describe how neutrons interact with a nucleus across a range of specific energies. Because these energies vary and impact dozens of areas in nuclear science, the SAMMY code was specifically developed by ORNL to refine this data.

Using an approach that works to incorporate uncertainties and hone the data, SAMMY fits experimental data with previously measured resonance parameters for individual isotopes. These resonance parameters are incorporated in the evaluated nuclear data libraries and, with the help of the SAMMY code, become key inputs for modeling and simulating nuclear reactor performance.

"For this work, we applied SAMMY in reverse," said Jesse Brown, a nuclear data scientist in the Nuclear Data group. "We asked the code to identify and match fingerprints gathered through neutron transmission to determine an unknown sample composition. Fortunately, ORNL has the facilities to gather this data onsite at VENUS."

Enter VENUS, ORNL's Versatile Neutron Imaging Instrument

VENUS is a leading neutron imaging instrument located within the Spallation Neutron Source, a Department of Energy Office of Science user facility.

Among its many capabilities, VENUS is an ideal platform for probing materials because it offers a wide range of neutron energies, making it well-suited for identifying subtle nuclear "fingerprints" that distinguish one isotope from another.

In this work, researchers used an approach called neutron resonance transmission analysis (NRTA) to study candidate materials known for their isotopic complexity. This approach is especially useful for materials that are difficult to analyze with traditional techniques because they are heavily shielded, mixed with other materials, or must remain intact.

To perform NRTA, researchers used VENUS to direct a beam of neutrons through a sample and measure how neutrons moved through it at different energies. Researchers carefully calibrated VENUS's resolution function, or how precisely it can manage neutron energy, to focus on energy regions where many isotopes show clear resonance patterns.

"VENUS was designed and built with careful shielding upstream of the measurement area to allow precise measurements such as neutron resonance cross-sections" said Hassina Bilheux, a distinguished senior neutron imaging scientist at the Spallation Neutron Source. It is very rewarding to see years of work on building VENUS pay off for nuclear data experiments."

A perfect match

To demonstrate how SAMMY can be used to effectively match materials to data produced by VENUS, researchers selected three candidate samples of gold, tantalum and hafnium.

Gold and tantalum served as baseline materials, allowing the team to verify SAMMY's ability to accurately fit and model high-quality data produced by VENUS. Natural hafnium, a material used in control rods of nuclear reactors, was chosen specifically for its complexity.

"Gold and tantalum are relatively simple, isotopically speaking," said Leal. "Natural hafnium is not. It contains six different isotopes, and their neutron signatures overlap."

After Bilheux's team gathered transmission measurements from each sample, they shared the data with Leal and other members of ORNL's Nuclear Data Group. The team used SAMMY in its traditional format and a modified format designed to streamline hypothesis testing across a library of potential isotopes. Both versions yielded strong results, demonstrating that SAMMY could differentiate isotopes by unique resonance signatures.

"Being able to separate those signals shows that SAMMY, combined with high-quality data from VENUS, can identify real-world materials with complex compositions," said Leal. "This finding is important for using these tools for other applications, like NDA testing of unknown materials."

"This study clearly demonstrates the critical role of high-quality experimental data produced at VENUS," said Klaus Guber, Nuclear Data Group leader. The rigor and precision of these measurements provided the foundation necessary for the analysis. Without them, SAMMY would not have been able to achieve a meaningful or reliable solution."

From data to insights: Applications for non-destructive testing

Together, VENUS and SAMMY form a complementary pair. VENUS provides precise neutron transmission data, while SAMMY uses that information to extract meaningful insights from samples. Combined, the technologies represent a new capability with several national security applications, specifically in nuclear safeguards, forensics and post irradiation examination.

"The partnership was a unique match in evaluating the VENUS beamline performance and precisely measuring nuclear data at unprecedented acquisition times of minutes rather than day," said Bilheux. "This work demonstrates how impactful VENUS is for future NDA testing."

"This approach offers another way to perform NDA testing and adds another layer of confidence confirmed by data," said Leal. "We can verify materials using SAMMY in a way that's accurate, efficient, and non-destructive."

This effort also demonstrates another perfect match, ORNL's world-class facilities and leading expertise. Where an experiment of this scope might normally involve dozens of researchers coordinating efforts across the globe, the coupling of SAMMY and VENUS benefited from geographic proximity and a partnership across ORNL's scientific disciplines.

"Individually, these are outstanding capabilities. Together, we're generating precise measurements and analysis, and applying those findings to real-world challenges right here on ORNL's campus," said Leal. "That partnership is what makes a difference."

This work was supported by the U.S. Department of Energy's Nuclear Criticality Safety Program.

ORNL is committed to supporting U.S. energy needs by pursuing strategic research that advances a wide variety of affordable, abundant and competitive nuclear technologies, and strengthens national security. The lab's scientific expertise and world-class facilities are often the first step in advancing nuclear energy innovations.

UT-Battelle manages ORNL for the DOE's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit energy.gov/science. - Liz McCrory