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 we have measured the energy splitting of the pionic 5g-4f and 5f-4d transitions in Ti. 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 Schr8dinger equation and from small corrections due to vacuum polarization, strong interaction, and electron screening. Part II. We have 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, we have observed that the Ta Ka1 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.