The enrichment of the neon isotopes in a thermoacoustic device is demonstrated. Because the thermal diffusion ratio of neon is small, an apparatus longer than a wavelength was necessary in order to easily observe the separation. The device was modular and extensible, so that arbitrarily large separations could in principle be obtained. The acoustic duct was a series of multiple, identical quarter-wavelength modules with side-branch drivers. In this way, waveforms close to that of a traveling wave were maintained in the duct, despite the high acoustic attenuation caused by the duct’s small diameter and large length. The concentrations of the isotopes were measured at one end of the duct using a quadrupole mass spectrometer. For the operating frequency of 227 Hz, the maximum separation gradient obtained was 0.43%/m, and mole fluxes at zero gradient as high as 3 nmol/s were observed. Effects of turbulence, though not observed, are also discussed, and the scaling properties of this method are compared with those of traditional mixture-separation methods.

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See Handbook of Chemistry and Physics, 64th ed. (CRC Press, Boca Raton, FL. 1984), p. B-235. Besides the two main isotopes, Ne21 is present at a concentration of 0.27%.
10.
As a measure of the difficulty in separating the neon isotopes compared to He–Ar mixtures, the 157-Hz neon data described below can be compared with data we obtained at the same frequency after filling this apparatus with a sample mixture of 55–45 He–Ar, which has the same sound speed as neon. In He–Ar, with a pressure amplitude of 2650 Pa, the apparatus produced concentration differences Δn∼0.4 across the duct—more than 50 times larger than the Δn obtained with 91–9 Ne20Ne22 mixtures at the same operating frequency.
11.
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8510B pressure transducer, Endevco, San Juan Capistrano, CA; http://www.endevco.com;
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23.
The reader may notice that the equilibrium concentration in Fig. 4 before separation appears to be 9.53% rather than the 9.22% quoted in Ref. 9. We attribute this to an error in the calibration of the mass spectrometer.
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28.
Reference 25, Eqs. (4.54) and (4.70) with dTm/dx=0.
29.
The analytical calculation of Δn across a module of arbitrary L and Δφ becomes tractable when turbulence and steady diffusion are ignored and the wave number is taken to be real.
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