ISOTOPE SHIFT MEASUREMENTS FOR SUPERDEFORMED FISSION ISOMERIC STATES

Optical isotope shift measurements have been performed for the Am-240, 242(f) fission isomers with low target production rates of 10 s(-1) em ploying resonance ionization spectroscopy in a buffer gas cell. Isotop e shift ratios IS240f,241/IS243,241 = 39.2(8) and IS242f,241/IS243,241 = 41.4(8) have been measured at the 500.02 nm transition. A differenc e in the nuclear mean charge radii delta[r(2)](opt)(242f,241) = 5.34(2 8) fm(2) and an intrinsic quadrupole moment Q(20)(242f) = (35.5 +/- 1. 0(st) +/- 1.2(mod)) e b have been deduced, neglecting the nuclear pola rization correction. The small difference delta Q(20)(242f,240f) = 0.6 3(8) e b demonstrates the stability of the deformation if two neutrons are removed. [S0031-9007(97)04957-0].