  Several experimental studies have reported thermally activated behavior of
the mechanical response of solid Helium-4 which does not fit into the model of
thermally activated Frenkel pairs in an ideal crystal. The purpose of the
present work is to investigate how structural topological defects modify the
response. Using quantum Monte Carlo Worm Algorithm, we study temperature
dependence of fluctuations of the total number of particles in samples of hcp
solid Helium-4 containing several types of dislocations. Such fluctuations can
be described by the thermal activation law with the activation energy dependent
strongly on the type of the dislocation and the crystal density. The extracted
values cover a range from about 1K to 20K. It is also found that annihilation
of a jog-antijog pair can produce a local region of the solid characterized by
the orthorhombic symmetry. This serendipitous observation suggests that hcp
solid Helium-4 can undergo a displacive phase transition into the orthorhombic
crystal under uniaxial stress of about 10-15%
