Nuclear moments of the radioactive isotope La determined by collinear fast-beam laser spectroscopy

Iimura, Hideki  ; Schuessler, H. A.*; Buchinger, F.*; Cocolios, T.*; Crawford, J. E.*; Gulick, S.*; Lee, J. K. P.*; Levy, C. D. P.*; Pearson, M.*; Lioubimov, V.*; Zhu, F.*; Rikovska, J.*; Rosner, S. D.*; Thompson, R.*; Wyss, R.*

We report measurements of the hyperfine structure constants of La (N=74) as an initial step to further exploring the neutron deficient rare-earth region where a sudden onset of nuclear deformation is predicted theoretically around N=74. This work is an extension of our earlier off-line experiments on La to on-line laser spectroscopy. The radioactive isotope La (T=59 min) was produced by means of a spallation reaction using a proton beam from TRIUMF cyclotron. The hyperfine spectra were observed by using the method of collinear fast-beam laser spectroscopy. From the obtained hyperfine constants, the nuclear moments of La were derived. In order to arrive at an understanding of the nuclear structure of La, we have carried out particle triaxial-rotor calculations. The results from the calculation reproduce well the experimental values when a triaxial shape is assumed for La.