Experimental Techniques

Abstract

Optical isotope shifts between isotopes that differ by two in their mass number are usually comparable with or smaller than the Doppler width of spectral lines from a low-temperature light source. This is shown in Fig. 8.1 where the curves are both for spectral lines of wavelength 500 nm. The curve labeled “width” is the Doppler width for a source temperature of 500 K; that labeled “NMS” is the normal mass shift. The labeled points are examples (where the wavelength is only roughly of the order of 500 nm in some cases) of large specific mass shifts (given by numbers) and field shifts involving one outer s electron (given by letters). Since the great majority of isotope shifts are smaller than these examples, it can be seen that isotope shifts are rarely larger than the Doppler width even for a light source run at such a low temperature as 500 K.