Spectroscopy along Decay Chains of Element 114, Flerovium

This thesis focusses on a nuclear spectroscopy experiment conducted to study α-decay chains stemming from isotopes of flerovium (element Z = 114). An upgraded TASISpec decay station was placed behind the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. The fusion-evaporation reactions ⁴⁸Ca + ²⁴²Pu and ⁴⁸Ca + ²⁴⁴Pu provided a total of 29 flerovium decay chains. The measurement of two new types of even-even flerovium decay chains, starting from ²⁸⁶Fl and ²⁸⁸Fl, respectively, marked the discoveries of (i) an excited state in ²⁸²Cn and (ii) the isotope ²⁸⁰Ds. The observations gave further insights into the location of the coveted Island of Stability. With fifteen new decay chains starting from ²⁸⁹Fl, the global data set was doubled for this isotope. Measured decay properties of these chains could provide new evidence of α-decay fine structure of odd-A superheavy nuclei, as predicted by theoretical calculations.

The papers included in this thesis cover various aspects of the flerovium experiment. The chapters complement the publications with background information and further details. They include an introduction to the research field of superheavy nuclei, detector development efforts, a description of the experimental setup as well as information on the data analysis and the simulations performed. The chapters also provide a summary of the main results and overarching outlook perspectives.

In Paper I, the processing of digitised silicon preamplifier signals were applied to short-lived α-decaying nuclei North-East of Pb. Further preparatory aspects of the experiment as well as applied spectroscopic tools, are covered in Paper III. The TASISpec decay station was upgraded with novel Compex germanium detectors, and their characterisation is given in Paper II. Paper V presents detailed information on the data analysis and statistical assessments applied to the flerovium decay chains. Highlights from the even-even Fl-decay chains are presented in Paper IV and as a press release in Paper VII. Finally, the main findings of the odd-A, ²⁸⁹Fl, decay chains form Paper VI.