We report measurements of the distribution of rotons generated by a particles interacting in a bath of superfluid helium. The roton flux is found to be anisotropic; it is about 4 times larger transverse to the track direction than along it. This asymmetry may provide a powerful tool in particle and astrophysics experiments where sensitivity to low energy recoil track direction is important.

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This letter reports experiments on the conductance of mesoscopic Bi films which are polycrystalline and contain single atomic two-level tunneling systems. These defects act as electron scattering centers and give rise to random telegraph signals in the conductance. External strain, applied to the samples at low temperatures, changes the asymmetry energy of the double-well potential of the tunneling particle and thus controls its average dwell time in either well. The measurements allow to determine in a direct way the deformation potential of a particular tunneling defect.