X-ray-assisted nuclear excitation by electron capture in optical laser-generated plasmas

This is the authors' abstract. We don't add key points for this paper.

X-ray-assisted nuclear excitation by electron capture (NEEC) into inner-shell atomic holes in a plasma environment generated by strong optical lasers is investigated theoretically. The considered scenario involves the interaction of a strong optical laser with a solid-state nuclear target leading to the generation of a plasma. In addition, intense x-ray radiation from the X-ray Free Electron Laser (XFEL) produces inner-shell holes in the plasma ions, into which NEEC may occur. As a case study, we consider the 4.85-keV transition starting from the 2.4-MeV long-lived ⁹³ᵐMo isomer that can be used to release the energy stored in this metastable nuclear state. We find that the recombination into 2p1/2 inner-shell holes is most efficient in driving the nuclear transition. The generation of inner-shell holes while the plasma is at a temperature of a few hundred eV can allow optimal conditions for NEEC, which are otherwise reached for steady-state plasma conditions in thermodynamical equilibrium only at few keV. The combination of x-ray and optical lasers presents two advantages: First, NEEC rates can be maximized at plasma temperatures where the photoexcitation rate remains low. Second, with mJ-class optical lasers and an XFEL repetition rate of 10 kHz, the NEEC excitation number can reach ≈1 depleted isomer per second and is competitive with scenarios recently envisaged at petawatt-class lasers.