= Solution
{c}
The closest components above differ by $\Delta\nu_{\min}=\mu_BB/(2h)\simeq7.0\,\mathrm{GHz\,T^{-1}}B$. At $B=0.1\,\mathrm T$, their separation is about $0.70\,\mathrm{GHz}$. A visible <spectral line> near $500\,\mathrm{nm}$ would consequently require <spectral resolving power> of order $\nu/\Delta\nu_{\min}\simeq9\times10^5$. An ordinary low-resolution <spectrometer> would merge the components.
A suitable arrangement places an excited low-pressure <strontium> discharge or a transversely observed <atomic beam> between wide electromagnet pole pieces. Collect the emission perpendicular to the <magnetic field>, select the desired <spectral line> with a prefilter or <monochromator>, and send it through a high-finesse scanning <Fabry–Pérot interferometer> to a detector. A rotatable linear <polarizer> separates the two $\pi$ components from the four $\sigma$ components. Calibrate both the interferometer's <free spectral range> and the local <magnetic field>; take zero-field and several field-strength scans, and fit component positions against $B$.
The <magnetic field> should be uniform across the viewed volume, with its associated <Zeeman splitting> larger than the combined <natural linewidth>, <Doppler broadening>, <pressure broadening> and instrumental width, but much smaller than the separations of the relevant <atomic fine-structure levels>. A collimated transverse <atomic beam>, low collision rate and restricted collection angle reduce unwanted <spectral line broadening>. Avoid appreciable <power broadening>, resolve or model <isotope> and <hyperfine structure>, and check for self-<absorption>. A zero-field scan and the predicted linear scaling help distinguish actual <Zeeman splitting> components from neighbouring <spectral lines>.
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