Direct Measurement of Desorption Kinetics of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ at Low Temperatures

A direct method for measuring the desorption time constant of flash-desorbed ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ films (≲ 1 monolayer), adsorbed on Nichrome or Constantan heaters, is described. A time constant $\tau$ is found which behaves as $\tau ={\tau }_0\exp \left[\frac{E}{T_s}\right]$, where $T_s$ is the heater temperature. The value for the characteristic lifetime ${\tau }_0$ is ${10}^{-9\mathrm{}}$-${10}^{-10\mathrm{}}$ sec, orders of magnitude shorter than that previously reported. The measured energy parameter $E$ was found to be $\sim \frac{2}{3}$ of the chemical potential.