Hyperfine Structures in the Atomic Spectrum of Calcium

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Abstract
The spectrum of calcium was excited in a hollow cathode tube cooled with liquid hydrogen. The use of a sample of calcium enriched in the isotope 43 allowed hyperfine structures to be resolved in the are line λ6103 (4s4p 3P0-4s5s3S1) and the spark lines λ3933 (4s 2S1/2-4p 2P3/2) and λ3968 (4s 2S1/2-4p 2P1/2), from which an approximate value of - 1.2 nuclear moments (n.m.) for the nuclear magnetic moment was derived. The intensity ratio of the components of the are line was found to be affected by self-absorption due to the metastability of the lower term. After correction for this effect, the measured intensity ratio agreed best with a value of 7/2 for the nuclear spin. After publication of the value of the gyromagnetic ratio by Jeffries, the measurements of the width of splitting of the spark lines a lowed the nuclear spin to be determined conclusively as I = 7/2, in agreement with the predictions from the shell model and the value deduced from the strength of the nuclear resonance signal. The splitting of the ground term, 0.109±0.002 cm-1, is 4% smaller than the value calculated from the gyromagnetic ratio by the use of the formulae of Goudsmit, Fermi, Segrè, Breit and Racah.

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