A review of the processes by which ultrasound is generated through the interaction of ionizing radiation and irradiated materials: some possible applications.

The production of acoustic waves following the absorption of energy deposited by ionizing radiation, with a consequent production of localized thermal spikes has been confirmed by a number of papers published in the physics literature. This paper reviews the basic theory and presents most of the supporting experimental data. Some of the experimental methods used and the results obtained are summarized. In addition to the rather straightforward and routine use of acoustic phenomena produced by ionizing radiation for the detection and measurements of such radiation, there are some special applications that appear to be especially attractive for medical physics. Some of these are unique to ionizing radiation in that the amplitude of the ultrasound wave is proportional to the energy deposited in small volumes at localized sites of these interactions, while others derive from methodologies already in use with nonionizing radiations. The detection and measurement of this ultrasonic radiation could possibly lead to methods for the study of such fundamental phenomenon as track structure, precision localization of therapeutic treatment beams, and even the possible imaging of internal anatomic structures to provide on-line portal images.