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Measured and Theoretical Kα X-Ray Emission Linewidths of U, Np, and Pu

Wessels A, Dean JW, Becker DT, Bennett DA, Carpenter MH, Croce M, Fowler JW, Gard JD et al.

Physical review letters, 2026

Abstract

We present measurements of the Kα_{1} and Kα_{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 Kα x-rays overlap with diagnostic gamma lines. We also present multiconfiguration Dirac-Fock calculations of the Kα 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.

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