The synthesis and study of the superheavy nuclei (SHN) is still one of the major challenges of modern nuclear physics. Experimental studies of hitherto unknown nuclei depend crucially on their identification in terms of atomic charge Z and nuclear mass A. To complete particle ID capabilities of the separator-spectrometer set-up S3 at GANIL-SPIRAL2, already providing a mass resolution sufficient to resolve the A of SHN, its focal plane detection system SIRIUS will be provided with X-ray detection for Z identification of the species of interest. The development of an X-ray detection system array, employing thin germanium crystals with thin entrance windows (based on so-called Low-Energy Photon Spectrometers (LEPS)), its integration in the SIRIUS set-up as well as its in-beam test and use for SHN decay spectroscopy will be the main tasks of the Ph.D. thesis. The Ph.D. student will be involved in SHN spectroscopic studies at GANIL and international accelerator laboratories like ANL, which serve as efficient preparation of the experiment campaigns planned at S3 which is scheduled to come online in 2024. This Ph.D. thesis work is an important ingredient for the preparation of the detection instrumentation needed for the S3 operation.