Isotope shift and hyperfine structure measurements at the242f Am fission isomer

Istope shift and hyperfine structure measurements have been performed for the^242fAm fission isomer with target production rates of only a few per second. The method is based on resonance ionization spectroscopy (RIS) in a buffer gas cell with radioactive decay detection of the ionization process (RADRIS). A relative isotope shift ratioX _exp=IS^242f,241/ IS^243,241=41.7±0.9 has been measured for the 500.02 nm transition corresponding to a nuclear parameter ^242f,241=5.4±0.3 fm². The analysis of the quadrupole moment based on the deformed Fermi-model of the nuclear charge distribution including second order corrections results inQ ₂₀=38.2 ±1.4( _–0.8 ^+0.4 )_model eb. The measurement of the hyperfine structure splitting of the transition at 466.28 nm yields a negativeg-factor and a nuclear spin ofI=2 orI=3.Work supported by the Bundesministerium für Bildung und Forschung under contract 06 MZ 5661.