Fig. 1. Feynman diagrams of the possible mechanisms for producing nuclear isomers in plasma: (a) CE; (b) NEEC. “○e” indicates that the electron is in an atomically bound state and “e” that it is in a continuum state. N indicates that the nucleus is in its ground state and N∗ that it is in an excited state.

Fig. 2. Energy level diagrams of (a) ¹⁰⁷Ag and (b) ⁷³Ge. The nucleus can be excited to its isomeric states directly, or it can first be excited to higher states, with subsequent decay to its isomeric states.

Fig. 3. Nanowire array target model used in the simulation. The simulation involves modeling several adjustable parameters, including the wire length L, wire diameter D, distance between wires S, and substrate thickness d.

Fig. 4. Representative spectra of electrons captured at different locations at times (a) t = 18 fs and (b) t = 22 fs. Arrows indicate the directions of the electron velocities, and the color shading indicates the respective energies. The periodicity in the electron directions is attributed to the oscillations of the laser electromagnetic field.

Fig. 5. Spectra of electron energy at different times for (a) Ag and (b) Ge. The color shading indicates N_e log₁₀N_e with units keV⁻¹ fs⁻¹ J⁻¹ presents energy spectra of Ag and Ge at different times. Both Ag and Ge electrons reach peak energy levels at ∼35 fs, coinciding with the exit of the primary laser beam from the nanowire array. Subsequently, the electron energies (temperature) decrease. A significant number of electrons exceed the energy thresholds for CE of ¹⁰⁷Ag and ⁷³Ge. Furthermore, a significant proportion of electrons satisfy the energy requirements for NEEC resonance in ¹⁰⁷Ag and ⁷³Ge, as described in Sec. II.

Fig. 6. Profiles of ion number Nionq,t in various charge states q for (a) Ag and (b) Ge at different times t. The color shading indicates log10Nionq,t, with units of q⁻¹ fs⁻¹ J⁻¹.

Fig. 7. Representative results from PIC simulations for (a) ¹⁰⁷Ag and (b) ⁷³Ge: electron energy spectra dN_e/dE_e(t) at times t = 50, 100, and 150 fs, CE cross-section σ(E_e), and their product [dN_e/dE_e(t)]σ(E_e). The products are plotted to delineate the major contributory sources, since the reaction rates are proportional to [dN_e/dE_e(t)]σ(E_e).

Fig. 8. Production rates, normalized to laser energy, of ¹⁰⁷Ag and ⁷³Ge isomers through CE.

Fig. 9. NEEC resonance strength S_NEEC-GSA(E_r, q) as a function of charge state q and resonance energy E_r for for (a) ^107mAg and (b) ^73mGe.

Fig. 10. (a) Production rate r_q(t) of ^73mGe by NEEC as a function of time t for different ion charge states q. (b) Total r_q(t), given by r_total(t) = ∑_qr_q(t).