In principle, any fission neutron or gamma interaction with matter which produces measurable effects can be used for rcactor-power measurements Practical considerations, however, limit the choice to a few The commonly used detectors have evolved through a selection process based on considerations of signal strength, response time, and tolerance of interfering radiations

The radiation detector produces an electrical signal that overrides typical electronic-circuit noise levels If the detector is to be used in reactor protection systems, its signal must be reliable and its response time should be short In event of a reactor accident or major component failure, the detector may have to respond rapidly to initiate a shutdown before damage can occur I he time constants of signal conditioning circuits are longer than detector response and normally are limiting for protection system considerations In addition, a strong gamma background can obscure the neutron signal Fission product gamma radiation is always a large contributor to the background gammas in power reactors

Despite considerable research and development on other types most operating detectors depend on gas ionization Generally, gas ionization detectors5 can be made to have sufficient sensitivity without excessive size and to have a wide operating range, a fast response time, and adequate radiation selectivity

Most neutron sensors utilize gas ionization caused bv charged particles emitted in neutron-induced fission reactions in 23SU or m (n a) reactions in boron Gamma sensors detect the ionization caused by Compton electrons