Laser spectroscopy of a thermal atomic beam of natural lanthanum has been performed. An active filtering technique has been used to remove spurious cavity modes from the laser output, leading to unambiguous identification of hyperfine structure associated with 138La. Hyperfine structure coefficients and isotope shifts for several transitions of the isotopes 138La and 139La are presented.
An isomer has been detected in 171 Hf with a half-life of T 1/2 = 29.5(9) s. The state was populated in the 170 Yb(α,3n) 171m Hf reaction at a beam energy of E α = 50 MeV in an on-line ion guide isotope separator. The isomeric 171m Hf + beam was extracted from the ion guide, mass-analysed and implanted in the surface of a microchannel-plate. The half-life of the collected activity was measured from the decay of the microchannel-plate count rate. We associate the isomer with the first excited state in 171 Hf with spin 1/2 − at an excitation energy of 22(2) keV.
An alternative approach is proposed for the analysis of optical isotope shifts. It is shown that for many elements a plot of the shift for one isotope pair against that for another pair for a series of transitions is linear. In certain circumstances the gradient of this plot gives the ratio of the change in mean square charge radii of the isotope pairs directly. Alternatively the plot is helpful in making judgements as to whether specific mass effects are likely to be negligible, with the field shift dominant, and hence assisting other methods of analysis. The possible range of validity is discussed.
The first successful application of an ion-guide separator (IGISOL) for collinear laser spectroscopy of radioisotopes has achieved an efficiency comparable with the best obtained with catcher-ionizer facilities. The ion beam energy spread was determined to be less than 6 eV, allowing laser fluorescence resonance signals for the radioisotopes to be detected with high resolution and sensitivity. Applications of this technique to measuring nuclear properties of refractory elements and short lived isomers promises to be particularly advantageous.
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