Experimental study of an initially pressurized water target irradiated by a proton beam

This experimental visualization study was conducted to investigate and define the phenomena of an initially pressurized liquid water target that can prevent the boiling of water when the target is irradiated with a 30-MeV proton beam produced using the MC-50 Cyclotron at Korea Institute of Radiological and Medical Sciences. At various initial pressures and proton beam currents, the behavior of the target water was investigated using a complementary metal-oxide-semiconductor camera. We confirmed that an appropriate initial pressure could indeed prevent local bulk boiling, and be determined by solving Rayleigh's equation and the Clausius-Clapeyron equation for homogeneous bubble growth using the measured bubble size generated at the Bragg-peak region. The saturation temperature of the initial pressure must be higher than the calculated local water temperature at the Bragg-peak region. The final pressure of the water target increased proportionally with the initial pressure and proton beam current. The penetration depth of the beam varied with beam current and slightly with the final pressure, as evidenced by the emission of blue light in all experimental cases.