Specifies the characteristics of reference sources and reference radiations which take the form of adequately characterized large-area sources specified in terms of activity (per unit area) and surface emission rate. Regulatory documents refer to surface contamination in terms of activity per unit area, while the response of monitoring instruments is related directly to the radiation emitted (i.e. they indicate surface emission rate). Does not describe the procedure involved in the use of these sources (see e.g. IEC Publication 325).