The purpose of this standard is to specify performance criteria and type-test methods used to evaluate portable radiation detection instruments. These instruments are used for detection of photon emitting radioactive materials and photon exposure rates. Instruments are used for the purposes of detection@ interdiction and prevention. Instruments may include alarms to indicate an increase in exposure rate. This standard does not apply to instruments that are primarily intended to provide a measurement of dose equivalent rate. In a departure from other DHS-related ANSI N42 instruments standards@ some issues of Radiological/Nuclear initial response (R/N initial response) are discussed. A tactical description of R/N initial response is provided in this revised standard in Annex H and is generally linked to related R/N initial response instrumentation situations in ANSI N42.32@ ANSI N42.34@ ANSI N42.35@ ANSI N42.38@ ANSI N42.43@ ANSI N42.53@ and directly linked to ANSI N42.49A. This direct link is from a portable instrument with low exposure rate range to a portable instrument of a much higher exposure rate range. This instrument range change may be necessary in some R/N initial response situations. Purpose This standard specifies the performance criteria and test methodologies for portable radiation detection instrumentation used for detection of photon emitting radioactive materials for Homeland Security applications. Annex H@ R/N initial response Applications for Preventive Radiological/Nuclear Detection (PRND) Equipment@ provides guidance and considerations for use of PRND equipment in R/N initial response situations.