1.1 This practice covers the procedures for preparation, testing and using the acidic aqueous ferrous ammonium sulfate solution dosimetry system to measure absorbed dose to water when exposed to ionizing radiation. The system consists of a dosimeter and appropriate analytical instrumentation. The system will be referred to as the Fricke system. It is classified as a reference-standard dosimetry system (see ISO/ASTM 51261).1.2 The practice describes the spectrophotometric analysis proce