March 18, 2025• Physics 18, s33
Measuring how efficiently an isotope captures neutrons of various energies both confirms and refutes some surprising recent results.
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When an atomic nucleus is struck by a neutron, it has a chance of capturing that neutron and becoming a heavier isotope. In 2019, physicists studying this process in zirconium-88 (88Zr) made a surprising discovery: The isotope’s neutron-capture cross section for low-energy (thermal) neutrons was tens of thousands of times larger than theory predicted [1]. Extrapolating from that result, they calculated 88Zr’s neutron-capture cross section across all neutron energies—its so-called resonance integral—and found it to be 2 orders of magnitude larger than any previously measured. Now Thanos Stamatopoulos at Los Alamos National Laboratory in New Mexico and colleagues have tested the validity of that extrapolation [2a, 3]. Taking energy-resolved measurements of 88Zr’s neutron-capture cross section over a broad energy range, the team derived a thermal-neutron-capture cross section roughly in line with the surprise result from 2019, but the resonance integral turned out to be nearly 200 times smaller.
Conventionally, neutron-capture cross sections are measured by bombarding a sample with neutrons and then measuring the gamma-ray signature produced when some of those neutrons are captured. Using this method for a radioactive isotope such as 88Zr is difficult because the detector can be overwhelmed by gamma radiation from the decaying isotope itself. Instead, Stamatopoulos and colleagues fired a broad-spectrum neutron beam at a 88Zr target and measured the flux of neutrons that traversed the sample to reach a detector a few meters beyond. Since higher-energy neutrons arrived at the detectors sooner, the values obtained for the neutron-capture cross section were intrinsically energy resolved. The measurements revealed that 88Zr’s capture cross section is dominated by a single large peak at low energies, and then it plummets at high energies. Extrapolating this low-energy capture efficiency yielded the previous high resonance integral.
–Marric Stephens
Marric Stephens is a Corresponding Editor for Physics Magazine based in Bristol, UK.
References
J. A. Shusterman et al., “The surprisingly large neutron capture cross-section of 88Zr,” Nature 565, 328 (2019).
A. Stamatopoulos et al., “Origin of the enormous 88Zr neutron-capture cross section and quantifying its impact on applications,” Phys. Rev. Lett. 134, 112702 (2025); .
A. Stamatopoulos et al., “First study of 88Zr + n at DICER at LANSCE at energies up to 500 eV and relevance to explosive environments,” Phys. Rev. C 111, 034613 (2025).
Discovery of the Origin of the Enormous Zr88 Neutron-Capture Cross Section and Quantifying Its Impact on Applications
Athanasios Stamatopoulos, Paul E. Koehler, Brad DiGiovine, Veronika Mocko, Artem Matyskin, Christiaan Vermeulen, Aaron Couture, Andrew Cooper, Jonathan Morrell, and Ellen O’Brien
Phys. Rev. Lett. 134, 112702 (2025)
Published March 18, 2025
First study of Zr88+n at DICER at LANSCE at energies up to 500 eV and relevance to explosive environments
Athanasios Stamatopoulos, Paul E. Koehler, Brad DiGiovine, Veronika Mocko, Artem Matyskin, Christiaan Vermeulen, Aaron Couture, Andrew Cooper, Jonathan Morrell, Ellen O'Brien, Dusan Kral, and John Ullmann
Phys. Rev. C 111, 034613 (2025)
Published March 18, 2025
Subject Areas
Nuclear Physics
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