The directional dose equivalent H'(0.07, ) at the point of interest in the actual radiation field is the dose equivalent which would be generated in the associated expanded radiation field at a depth of 0.07 mm on the radius of the ICRU sphere which is oriented in the fixed direction . An expanded radiation field is an idealized radiation field in which the particle flux density and the energy and direction distribution of the radiation show the same values at all points of a sufficient volume as the actual radiation field at the point of interest.

Diagram of an expanded radiation field

Diagram of an expanded radiation field