Towards the island of superheavy stability - Prompt spectroscopy of 246Fm and 256Rf nuclei

The region of trans-fermium nuclei (Z = 100 to 104) is the last region of the nuclides chart to be accessible to spectroscopic measurements. It therefore provides the ultimate anchor points for nuclear models. This region also lies on the path of the alpha-decay chains of the super-heavy elements. This region represents the limit of today's spectroscopic capabilities. It therefore requires technological developments in order to overcome these limits. My thesis focuses on various aspects of the spectroscopy of trans-fermium nuclei. I took part in the development of the TNT2D digital acquisition cards for germanium detectors. I validated their use on the gamma-ray spectrometer JUROGAM during an in-beam experiment and demonstrated the gain compared to an analogue acquisition system. These tests were part of the developments needed to secure a study of the prompt spectroscopy of 256Rf. The preparation of this experiment also lead me to work on the development of a 50Ti beam. For that purpose, I studied and tested the use of titanium organo-metallic compounds compatible with the MIVOC technique. In parallel, I studied the use of metallic and oxide titanium pellets with an inductive oven newly developed at the University of Jyvaeskylae. In addition to these developments, I had the opportunity to study the in-beam prompt spectroscopy of 246Fm at the University of Jyvaeskylae. The measurements yielded a rotational band built on the ground state of 246Fm. This band has been observed up to the level 16+ and shows a behaviour quite similar to the neighbouring even-even isotopes, except for the top of the band for which a wider statistics is necessary in order to conclude. (author)