Detection of the isotopes of lithium using the Faraday effect

Abstract

This paper is dedicated to Professor Douglas E. Ryan on the occasio~~ of his 65th birthdaySHI-L~AN JING and ROGER STEPHENS. Can. J. Chem. 65, 903 (1987) Lithium is atomised in an air-acetylene flame within a longitudinal magnetic field. Birefringent and dichroic signals are separately measured using a pulsed hollow cathode source. The arrangement is found to give isotopic selectivity and is useable down to concentrations of about 10 kg/mL. The signal ratio of birefringence: dichroism is found to be approximately independent of sample concentration at the high and low extremes of the calibration curve. However, severe distortions occur at intermediate concentrations. In addition, a reversal of signal magnitudes is observed between 6~i and 7Li. This effect is attributed primarily to a distortion of the source profile as a result of self-absorption, SHI-LIAN JING et ROGER STEPHENS. Can. J. Chem. 65, 903 (1987). Le lithium est atomis6 dans une flamme air/acCtylene comportant un champ magnCtique longitudinal. On peut faire des mesures sCpar6es des signaux birkfringent et dichroi'que en utilisant une source h cathode creuse et pulsCe. On a trouvC que cet arrangement donne une bonne sClectivitC isotopique et qu'on peut I'utiliser jusqu'a des concentrations aussi faibles que 10 pg/mL On a trouve que, aux limites extremement Clevie ou basse de la courbe de calibration, le rapport des signaux de birCfringence/dichroi'sme est pratiquement indCpendant de la concentration de I'Cchantillon. Toutefois, il se produits d'importantes distortions aux concentrations intermediaires. De plus, on observe un renversement des amplitudes des signaux entre le 6~i et le 7Li. On attribue principalement cet effet h une distortiondu profil de la sourcequi provient d'une auto-absorption.[Traduit par la revue] Introduction Magneto-optic rotation (MOR) has been used for the selective detection of the isotopes of lead (1). The technique employed the ratio of birefringence to dichroism in a Voigt optical configuration as a measurement parameter. The particular advantage of this approach is an ability to identify the different isotopes with an apparatus which uses a conventional, commercially available light source and atomiser: the method can tolerate the overlap of the hyperfine components of the atomic spectra without recourse to the use of isotopically pure sources and low pressure atomisers in order to optimise spectroscopic resolution.The ratio parameter is isotopically sensitive because the shape of an atomic line profile changes as the isotopic composition of the atomic vapor is altered. Since birefringence and dichroism show a different functional dependence on the form of the profile their ratio is automatically responsive to such variations. The ratio parameter is otherwise robust, being largely independent of source intensity and of background absorption by non-atomic species, and with a reasonable tolerance towards limited changes in the sample concentration.One disadvantage of the original apparatus proved to be a need for high samp...