We present measurements of the tunnel current and dynamic conductance of me
chanically controllable break junctions of Pt, Au, and Al at low temperatur
es in He-4 and He-3 gas environments. The study reveals that the previously
observed bias dependence of a reduction of the tunnel current due to the p
resence of adsorbed He has a typical width of 15-20 meV at 4.2 K, and is ce
ntered around zero bias. The tunnel resistance value at which the relative
reduction is maximal varies between 100 M Ohm and 1 G Ohm, and the maximum
value seems to be both material and sample dependent. The latter may be con
nected to differences in the exact electrode-surface geometries.