A spherical vessel of radius r1 is filled with gas. The molar mass of the gas is m, the temperature is T. Through a tube of radius r2 and length l, the gas enters the mass spectrometer. The cross section of molecules s is such that the conditions 1/nr2 > s > 1/nr1 are satisfied, where n is the gas concentration. At some point in time, an admixture of an isotope of the same gas appears in the center of the vessel, differing little in mass. Estimate the time after which the mass spectrometer will be able to detect the impurity.

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