LOW-TEMPERATURE HEAT RELEASE IN PURE ALUMINUM

We have measured the heat release of pure (6N) aluminium in the time r ange from 5h to 300h after cooling it from 85K to 200mK, in the normal and superconducting states. We measured a heat release that resembles quantitatively that from vitreous silica (SiO2) at times t greater th an or equal to 4 x 10(5) s indicating the existence of tunneling syste ms in agreement with previously published acoustic measurements. The t ime dependence of the heat release in Al is, however, weaker as that f ound in amorphous materials. No difference in the heat release has bee n measured in the normal and superconducting states.