Towards Optical Spectroscopy of the Element Nobelium (${\sf Z }= \mathsf{102}$) in a Buffer Gas Cell

For the investigation of the atomic level structure ofheavy elements which can only be produced at on-line facilitiessuch as GSI, a novel experimental procedure has been developed. Itis based on Radiation Detected Resonance Ionization Spectroscopy(RADRIS) and can be applied to elements like nobelium produced atrates of a few ions per second. Fusion reaction products areseparated from the primary beam by the velocity filter SHIP atGSI, stopped in a buffer gas cell, collected on a tantalumfilament and then re-evaporated as atoms. The ions produced byresonance ionization with tunable laser beams are detected viatheir characteristic α decay. First on-line experiments onα-active 155Yb, which is supposed to have an atomiclevel structure similar to nobelium, were performed. These testexperiments focused on the optimization of the collection andre-evaporation process of the radioactive ions, the laserionization efficiency and the detection via α decay. Anoverall efficiency for RADRIS of 0.8% with respect to the targetproduction rate was measured. While further improvements of thisefficiency are in progress it should already be sufficient for thesearch for atomic levels in nobelium.