There is strong observational evidence that a quasi-thermal population of electrons (or pairs) exists in compact X-ray sources. It is, however, unclear what mechanism thermalizes the particles. Here, two processes, Coulomb scattering and synchrotron self-absorption, that may be responsible for the thermalization, are reviewed. The parameter spaces in which respective process dominates are given...

Nuclear resonance fluorescence measurements provide direct sensitivity to ground-state transition widths by probing the photoexcitation process of nuclear resonances. A technique in Relative Self-Absorption (RSA) measurements, which are done at multiple absorber temperatures, was developed and tested with 27Al Darmstadt High Intensity Photon Setup Superconducting Linear Accelerator. The advanta...