Neutron ionization chambers

Abstract

One of the first particles on neutron detectors bears the title: Ionization of gases by neutrons 1). Neutrons are neutral, a fact that the author was aware of. Still, he, as well as others 2) in their first attempt to investigate neutrons, chose to take the full step from a neutron to the output signal. They did indeed record a signal and proved that a measurement device could be made: a current caused by neutrons flowed through the chamber. Several years elapsed before the ion chamber was explored as a neutron detector. Much more information about the neutron was gained from another device, the cloud chamber, which became popular at the expense of the development of the ion chamber. Any radiation detector may be used as a neutron detector if it contains or can be complemented by a material giving a conversion process, which transfers the information of interest to a charged particle. The recoil nucleus in a neutron scattering, the reaction products in a nuclear reaction, or the fission fragments in a nuclear fission may be used for the detection of the primary neutron. The devices used as detectors were often tubes. They were given the name “radiation counter tubes”, abbreviated as “counters’, which for neutron detection gave the combination “neutron counters”. A more general term is “neutron chambers”. The neutron chamber might be a neutron counter or a neutron spectrometer. Pure neutron counters to be described here are the boron-lined neutron chamber, the boron-trifluoride chamber and the fission chamber. Proton-recoil chambers and helium-3 chambers can be used as counters or spectrometers. Teh slowing-down neutron detectors are systems which include one of the above chamber types. By chamber we mean here a detector using a gas for the next step in the detection chain, the detection of the charged particles. The ion-chamber, proportionality, corona-discharge and Geiger-Müller range have all been used for neutron sensitive chambers. Ion-chambers are used both in pulse counting systems and in current measuring systems. The electron-ion pair clouds created in the chamber are in pulse detection systems sensed by voltage, charge or current sensitive preamplifiers. The current-pulse detection method has recently been popular for fission chambers because of their high signal-to-noise ratio and short pulse length. They are often referred to in the literature as current detectors, but should not be confused with the chamber systems which use the mean current as the information carrier.