BS IEC 60860:2014 IEC60860:2014@IEC2014 - 13 - 6.2.3 Neutron detectors 6.2.3.1 Requirements Since widely differing types of neutron detectors (scintillators, ionisation chambers, self powered activation detectors in moderators and junction diodes) with different energy response characteristics may be used in criticality alarm systems,it is only possible to give general guidelines on their use. The response of all neutron detectors shall be determined using the reference radiation (252Cf fission neutrons or other appropriate source). In addition for those detectors to be installed in a moderated neutron radiation field the response of the detectors shall be determined for such fields. The energy response of the detector may be measured using Iso standard neutron reference radiations (mono energetic radiations produced by an accelerator). The response of the detector to the moderated neutron field may then be assessed using published data on the neutron leakage spectrumforcritical assemblies.Alternatively,the detector response may be directly determined by exposure in a moderated neutron field simulated by a critical assembly or reactor of known dose rate. 6.2.3.2 Method oftest radiated during a criticality accident. The energy response to other reference neutron radiations should be also determined. The appropriate neutron energies as well as the criteria for acceptability should be specified uodn agreement between manufacturer and user. In this case, expose the detection subassembly to known dose rates and note the indications provided by the detector. The energy response of the detector shall comply with the criteria for acceptability. 6.3 Responsetime 6.3.1 Requirements The system shall be designed to produce the criticality alarm signal within O,3 s after the detection of criticality event. 6.3.2 Method of test produced within 0,3 s. 6.4 Alarm threshold of detection 6.4.1 Requirements The equipment shall respond to the direct gamma radiation, neutrons, or a combination of these radiations emitted during a criticality accident and shall meet the alarm threshold of detection specified by the purchaser. The alarm threshold of detection shall be such that when the equipment is installed, it will detect the equivalent of an absorbed neutron and (see 4.2). BSIEC 60860:2014 - 14 - IEC60860:2014IEC2014 6.4.2 Method of test The alarm threshold of detection, being the minimum dose to trigger the alarm, should be determined using an appropriate pulsed source of the test radiation. Tests should be made witharangeof radiationpulses of durationof about 1ms to3s. 6.5 Variation of responsewithangle of incidence 6.5.1 Requirements The angular dependent response of the detection subassembly shall bedetermined. 6.5.2 Method of test With a reference radiation source having a suitable activity and positioned at a given distance, thedetection subassembly shallberotated in steps of 3o°as specified below in a)and b)and the response to the test radiation shall be recorded. The activity and the distance shall be specified by the manufacturer. The distance shall exceed ten times the maximum dimension ofthedetectionsubassembly Detection subassembly rotated around a horizontal axis passing through the subassembly a)[ and orthogonal to the axis through the subassembly and the source. b)Detection subassembly rotated around a vertical axis passing through the subassembly detector.The results should be presented in the form of a polar chart. 6.6 Overload characteristics 6.6.1 Requirements For radiation doses or dose rates greater than those required to initiate the alarm, the warning subassembly shall be activated and remain so until reset. After the test the equipment shall during a period of at least 1 min. 6.6.2 Method of test This test shall be performed using a reactor or other appropriate source of radiation. The detection subassembly is exposed to the above dose rate and the alarm signal shall continue until reset. After the test the equipment shall