Nuclear spin determination of Y-100m by collinear laser spectroscopy of optically pumped ions

The nuclear spin of the tau(1/2) = 0.94 s isomer in Y-100 has been determined by collinear laser spectroscopy of optically pumped yttrium fission fragments at the IGISOL facility, JYFL. The isotopes 96,98,99,100Y were produced by the proton-induced fission of natural uranium, and studied on the 4d5s D-3(2) (1045 cm(-1)) -> 4d5p P-3(1) ( 32 124 cm(-1)) transition at 321.67 nm. Enhancement of the population of the metastable D-3(2) levelwas achieved by optically pumping the ground state population via the 5s(2) S-1(0) -> 4d5p P-1(1) transition at 363.31 nm while the ions were stored in a linear Paul trap. These data, when combined with previous spectroscopic results, give sufficient information for the nuclear spin of Y-100m to be determined unambiguously as I = 4. This spin assignment reveals that Y-100m has an unexpectedly large dynamic contribution to its quadrupole deformation.