Isotope shift measurement at 244fAm

Optical isotope shift measurements have been performed at the 244f Am fission isomers (T 1/2=1 ms) with low target production rates of 10/s employing resonance ionization spectroscopy in a buffer gas cell. The isotope shift ratio IS244f,241/IS243,241 = 42.0(9) has been measured at the 500.02 nm transition. A change in the nuclear mean charge radius \(\delta \langle r^2 \rangle _{{\text{opt}}}^{{\text{224}}f,241}\) = 5.41(31) fm2 and an intrinsic quadrupole moment \(Q_{{\text{20}}}^{{\text{224}}f}\) = 34.4 eb have been deduced with the deformed Fermi model. The small difference of the nuclear parameter Λ244f,242f = 0.069(21) fm2 between the 244f Am and 242f Am fission isomers results in a change of the quadrupole moment \(\delta Q_{{\text{20}}}^{{\text{224}}f,242f}\) eb only and demonstrates the stability of the superdeformation in the second potential minimum if two neutrons are removed.