This International Standard applies to the radiation detectors which are installed external to the core of nuclear reactors and which provide electrical input signals to the reactor’s control and instrumentation system. These detectors are usually gas-filled neutron detectors and this standard applies only to that type although many of its principles could be used for others, for example, gas-filled gamma radiation detectors. This standard therefore describes characteristics and tests methods for gas-filled radiation detectors used for the protection of nuclear reactors. The detectors subject to this standard are: • boron d.c. ionization chambers, • fission d.c. ionization chambers or fission pulse ionization chambers (fission counters), • boron trifluoride proportional pulse counter tubes, • helium-3 proportional pulse counter tubes. This standard may be used for d.c. ionization chambers for gamma radiation but the detectors discussed here are not used for personnel dosimetry. In-core radiation detectors are specifically addressed by IEC 60568 and IEC 61468. NOTE This list is not restrictive and it is hoped that all types of radiation detectors used in reactor installations will benefit from the present standard. The standard for tests also applies to connecting cables and connectors when they form an integral part of the detector.