  The thermal conductivity, heat capacity and heat release of NbTi, NbTi-H and
NbTi-D were measured at low temperatures. All three systems reveal low
temperature anomalies typical for structural glasses. It is shown that above a
concentration of 2\% H or D the tunneling states of the NbTi matrix disappear.
Therefore, for higher concentration it is a good system to proof how the change
of the mass of tunneling atoms influences the low temperature anomalies. For
the heat capacity we found the expected isotopic effect. However, the anomalous
isotopic effect observed for the heat release data cannot be explained within
the standard tunneling model. A surprising result is that tunneling systems
with very high barrier heights, even the systems with the maximum barrier
height, influence remarkable the heat capacity and the heat release data at low
temperatures. As a possible origin, we consider large-scale fluctuations in
thermal expansion which could generate anomalous two-level systems.
