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Impact of the small Dirac component on the valence electron density of actinides at their nuclei in solids

A. V. Nikolaev1, U. N. Kurelchuk2, and E. V. Tkalya3,2,4,5

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Phys. Rev. C 114, 034601 – Published 3 September, 2026

DOI: https://doi.org/10.1103/fmc6-8f4q

Abstract

We include the small components of valence states of actinides in the calculation scheme within the linear augmented plane wave method for solids and study their influence on the electron density at the actinide nuclear region, which is important for such processes as electron capture, beta decay, internal conversion, and others. The method was applied to Ac, Th, ThO2, and UO2. We find that, depending on the material, the electron density of valence electrons at the nucleus increases by a factor of 2.4–4.3, and this increase is due to the electron density from the small components of the 6p1/2 semicore states. Although accounting for the electron density of small components typically results in very small changes in the equilibrium lattice constant and bulk modulus, in some cases it reaches 0.007 Å for the lattice constant and 8 GPa for the bulk modulus. A refined electron density distribution in nucleus can be important for accurately describing electron-nuclear phenomena and for calculating characteristics measured in nuclear spectroscopy, especially for the low-energy clock transition in the Th229 nucleus.

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Phys. Rev. C 114, 034601– Published 3 September, 2026
  • Received 14 April 2026
  • Accepted 6 July 2026
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