Measured and Theoretical K⁢-alpha X-Ray Emission Linewidths of U, Np, and Pu

Published

September 10, 2026

Author(s)

Abigail Wessels, Jonathan William Dean, Daniel Becker, Douglas Bennett, Matthew Carpenter, Mark Croce, Joseph Fowler, Johnathon Gard, Paul Indelicato, Katrina Koehler, John Mates, Daniel McNeel, David Mercer, Daniel Schmidt, Katherine Schreiber, Daniel Swetz, Duc Vo, Sophie Weidenbenner, Joel Ullom

Abstract

We present measurements of the K-alpha-1 and K-alpha-2 natural x-ray linewidths of uranium, neptunium, and plutonium (Z=92, 93, 94) obtained using a superconducting transition-edge sensor microcalorimeter array. The relative uncertainties range from 0.5% to 1.5%, improving upon previous values by factors ranging from 3 to 8. These refined linewidths reduce systematic errors in gamma-ray spectroscopy assays of Pu-bearing materials, where K-alpha x-rays overlap with diagnostic gamma lines. We also present multiconfiguration Dirac-Fock calculations of the K-alpha linewidths for U, Np, and Pu, providing a benchmark for theory and experiment. These calculations reveal a discrepancy between ab initio theory and experiment possible to observe only with the improved experimental accuracy achieved in this work.

Citation

Physical Review Letters

Pub Type

Journals

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https://doi.org/10.1103/tcbz-kqk1

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Keywords

Atomic & molecular structure, Atomic spectra, Energy levels, Lifetimes & widths, Nuclear decay, First-principles calculations, Hartree-Fock methods, X-ray emission spectroscopy

Citation

Wessels, A. , Dean, J. , Becker, D. , Bennett, D. , Carpenter, M. , Croce, M. , Fowler, J. , Gard, J. , Indelicato, P. , Koehler, K. , Mates, J. , McNeel, D. , Mercer, D. , Schmidt, D. , Schreiber, K. , Swetz, D. , Vo, D. , Weidenbenner, S. and Ullom, J. (2026), Measured and Theoretical K⁢-alpha X-Ray Emission Linewidths of U, Np, and Pu, Physical Review Letters, [online], https://doi.org/10.1103/tcbz-kqk1, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956931 (Accessed September 24, 2026)

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