Acoustic signals of nonthermal origin from high energy protons in water

Abstract

Acoustic pulses generated by the passage of 30-GeV protons through water show evidence for the presence of a nonthermal source. In addition to the bipolar leading-compression signal expected from thermal shock, a tripolar leading-rarefaction component is observed. The component is dominant at 4°C, where the thermal signal should vanish. A space-charge effect may be the source of this component, since other proposed mechanisms leading to tripolar pulses should give a leading-compression signal.