The population of isomeric (metastable) excited states in nuclei within astrophysical environments associated with R-process freezeout can affect the final abundance of stable isotopes; these astrophysically relevant isomers are known as `astromers’ [1][2]. Astromers can be populated/depopulated via various electromagnetic mechanisms, generally via low excitation energy, short-lived states above the isomer. The population of these `astromers’ has been studied theoretically using the Planckian photon bath [1] in which a network of photo-nuclear excited states and subsequent relaxations is considered during the population of an astromer from its associated nuclear ground state.
Similarly, an isomer can be depopulated [2] with a much lower, yet albeit comparable electron flux via inelastic electron-scattering processes, which will necessarily also deplete the astrophysical isomer [3]. One such electromagnetic process is `nuclear excitation by electron capture’ (NEEC), which is the inverse of internal conversion, recently reported to deplete isomers terrestrially with a high [4], yet still refuted [5], excitation probability in a radioactive ion-beam scenario.
This presentation focuses around encouraging the development hot-dense-plasma experiments using the photon and electron flux available at current or in-development peta-Watt (PW) laser facilities, which allow experimentation into separating the electromagnetic mechanisms at play in depleting isomers. This will allow us to readily challenge the relevance of astromers in calculating the final abundance of isotopes in the cosmos.
[1] G. Wendell Misch et al. “Astromers: Nuclear Isomers in Astrophysics”. In: The Astrophysical Journal Supplement Series 252.1 (Dec. 2020), p. 2. doi: 10.3847/ 1538-4365/abc41d
[2] G. Wendell Misch, T. M. Sprouse, and M. R. Mumpower. “Astromers in the Radioactive Decay of r-process Nuclei”. In: The Astrophysical Journal Letters 913.1 (May 2021), p. L2. doi: 10.3847/2041- 8213/abfb74
[3] J. Carroll and C. Chiara. “Isomer depletion”. In: The European Physical Journal Special Topics (Apr. 2024). doi: 10.1140/epjs/s11734-024-01149-8
[4] C. Chiara et al. “Isomer depletion as experimental evidence of nuclear excitation by electron capture”. In: Nature Publishing Group 554.7691 (2018), pp. 216–218. doi: 10.1038/nature25483.
[5] Y. Wu, C. H. Keitel, and A. P´alffy. “93mMo isomer depletion via beam-based nuclear excitation by electron capture”.