Collisional relaxation in a fermionic gas

We propose a method to study the degeneracy of a trapped atomic gas of fermions through the relaxation of the motion of a test particle. In the degenerate regime, and for an energy of the test particle well below the Fermi energy, we show that the Fermi-Dirac statistics is responsible for a strong decrease in the relaxation rate. This method can be used to directly measure the temperature of the fermionic gas. [S1050-2947 (99)50506-4].