Experimental determination of the relativistic fine-structure splitting in a pionic atom and dependence of K x-ray energy upon the mode of excitation

Part I. Using a high-resolution crystal spectrometer the energy splitting of the pionic 5g-4f and 5f-4d transitions in Ti has been measured. The observed fine structure splitting of 85.2 +- 3.0 eV agrees with the calculated splitting of 88.1 eV, arising from the relativistic fine-structure correction term of the Klein-Gordon equation or the Relativistic Schroedinger equation and from small corrections due to vacuum polarization, strong interaction, and electron screening. Part II. It has been observed that the energies of K x rays in Ta, Eu, Lu, and W depend on the method of excitation of the atoms. For example, the energy of the Ta Kα1 x ray emitted after electron capture of 181W has been found to be lower by 0.78 +- 0.04 eV compared to the fluorescent Ta Kα1 x ray. Similarly, it has been observed that the Ta Kα1 x ray emitted after internal conversion following β-decay of 181Hf is higher by 0.7 +- 0.1 eV in energy compared to the same fluorescent Ta x ray. The observed shift in Ta cannot be explained by such known mechanisms as the chemical, magnetic hyperfine, isotope, isomer, and shake-off effects alone. However, these mechanisms seem to explain most of the observed shift in Eu, Lu, and W