Two-photon decay of K-shell vacancies in silver atoms

The spectral distributions for the two-photon decay modes of singly K-shell ionized silver atoms are determined by x-ray–x-ray coincidence measurements. Ag K-shell vacancies were induced by nuclear electron capture decay of radioactive cadmium isotopes ¹⁰⁹Cd and two-photon coincidences were taken back to back (180°) and at a 90° opening angle for the emission. Each of the two-photon transitions from the 2s, 3s, and 3d states exhibits unique angular and spectral distributions. The measurements agree nicely with relativistic self-consistent field calculations of Tong et al. Our results also confirm and extend the earlier experimental data of Ilakovac and co-workers with improved accuracy.