Sound wave generated by swift heavy ions

We irradiated samples of polycrystalline metals (Al and Cu) and ceramics (MgO and machinable ceramic) with a short-pulse beam of 3.54-GeV Xe ions and detected sound waves in ultrasonic frequencies with piezoelectric sensors on the surface. On the Al sample, waveforms were observed at different positions relative to the epicenter and were compared with those by 3.8-GeV Ar ion and YAG-laser irradiation. The gross structure of the waveform was similar between the Xe and laser irradiation, where we observed a shear wave which was not found in the Ar-beam irradiation. For the metal samples, the propagation time of the compression wave to the epicenter is shorter for the Xe ion than the laser irradiation. Using the time difference and separately-measured value of speed of sound, we estimated the depth of the sound source in metals and found that it is near the end of the ion range.