The concept of the angular differential dose of ionizing radiation and its measurement

Radiation-induced effects often depend not only on the absorbed dose but also on the distribution of directions from which it is delivered. This distribution can be described by using the angular differential dose, whose integral over all angles equals the integrated dose. A directional sensor was developed to measure this quantity. The design of the sensor is based on a carbon fiber, self-reading, electrometer dosimeter. Its sensitivity to the direction of incident gamma rays or x-rays makes it possible to measure dose or dose rate as a function of the angle of incident radiation. Experiments to demonstrate the properties of this sensor (Directional Dosimeter, DD) were conducted, using point sources of 137Cs. Results show that the sensor can detect and locate multiple 137Cs sources and determine the angular differential dose or angular differential dose rate in physical units of gray (tissue) per degree or grays per degree per minute. The DD was also used to scan and image the back-scatter from a water target of monodirectionally incident 137Cs 662 keV gamma rays.