Hyperfine structure and isotope shift measurements of long-lived La isotopes by collinear laser spectroscopy

Abstract

The La isotopes (Z = 57) are in a region of rapid transition from nuclei with nearly spherical shape (the singly magic 139La) to nuclei that are soft towards deformation, presenting a good opportunity to test various nuclear models. There exist two naturally occurring La isotopes: the stable 139La and the long-lived 138La (T 1/2 = 1.05 × 1011 y). The natural abundance of 138La is very low (0.090%). So far, there is no measurement of the hyperfine structure (HFS) and the isotope shift (IS) of 138LaII. In order to extract changes in mean-square nuclear charge radii from IS data on LaII, a detailed knowledge of the ionic structure of La is essential. Therefore, for future measurements of short-lived isotopes, we have measured the HFS and IS of several transitions in 138,139LaII with collinear laser ion-beam spectroscopy. In addition to these naturally occurring nuclides, measurements for accelerator produced 137La (6 × 104 y) were also made.