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Testing for the continuous spectrum of x rays predicted to accompany the photoejection of an atomic inner-shell electron

Cornell Affiliated Author(s)


Philip Jacobson
Andrija Rasovic
Arthur Campello
Chase Goddard
Matthew Dykes
Yuchao Chen
J. Ko
Stanislav Stoupin
Gwen Gardner
Justin Oh
Carl Franck


Echoing classical physics, quantum electrodynamics predicts the release of a spectral continuum of electromagnetic radiation upon the sudden acceleration of charged particles in quantum matter. Despite apparent theoretical success in describing sister nuclear processes, known as internal bremsstrahlung, following nuclear beta decay and capture, the situation of the photoejection of an electron from an inner shell of an atom, intra-atomic bremsstrahlung (IAB), is far from settled. In this paper we present fresh measurements which rely on contemporary signal processing as well as the high flux available from a synchrotron radiation source to revisit the problem by photoejecting electrons from the innermost shell of copper. We have sufficient sample statistics to measure the expected spectra at the level expected by contemporary theory. Furthermore, we employ sufficiently thin targets to overcome secondary scattering artifacts. Our approach applies the fluorescence coincidence method to guard against extraneous scattering and multiple incident photon processes. Our observations set a severe upper limit on the rate for IAB: We conclude that current theory overpredicts, by at least 5 sigma, the measured rate for -shell IAB in copper in the range of detected energies below the fluorescence energy. ©2021 American Physical Society

Date Published


Physical Review A








Group (Lab)

Carl Franck Group

Funding Source


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