A fissile neutron detection system includes a neutron moderator and a neutron detector disposed proximate such that a majority of the surface area of the neutron moderator is disposed proximate the neutron detector. Fissile neutrons impinge upon and enter the neutron moderator where the energy level of the fissile neutron is reduced to that of a thermal neutron. The thermal neutron may exit the moderator in any direction. Maximizing the surface area of the neutron moderator that is proximate the neutron detector beneficially improves the reliability and accuracy of the fissile neutron detection system by increasing the percentage of thermal neutrons that exit the neutron moderator and enter the neutron detector.

A neutron position detector according to an embodiment includes a tubular enclosure used as a cathode, an anode located at an axial center inside the enclosure, and a gas that includes a .sup.3He gas and an additive gas and is sealed inside the enclosure. The additive gas includes nitrogen as a quenching gas, and argon as a gas that reduces the ranges of reaction products as neutron and .sup.3He gas.

A neutron position detector according to an embodiment includes a tubular enclosure used as a cathode, an anode located at an axial center inside the enclosure, and a gas that includes a .sup.3He gas and an additive gas and is sealed inside the enclosure. The additive gas includes nitrogen as a quenching gas, and argon as a gas that reduces the ranges of reaction products as neutron and .sup.3He gas.

A radiation detector to monitor the neutron flux of a nuclear reactor or other high-radiation environment, that can withstand the high temperatures and radiation fields of such environment, is provided. A small dielectric substrate with a low neutron-activation cross section is provided. The substrate is coated with a neutron conversion material, such as uranium oxide or thorium oxide. One or more substrates form a micro-sized detection cavity that is filled with a detection gas. A voltage is provided across anode and cathode wires in the detection cavity. A neutron absorbed in the conversion material may release reaction products into the gas, causing ionization of the gas which then produces a current or voltage signal. The small detector volume minimizes energy deposition into the detection gas by competing particles such as gamma rays, fast electrons, and beta particles, and therefore minimizes false counts while retaining large signals from neutron interactions.

A radiation detector to monitor the neutron flux of a nuclear reactor or other high-radiation environment, that can withstand the high temperatures and radiation fields of such environment, is provided. A small dielectric substrate with a low neutron-activation cross section is provided. The substrate is coated with a neutron conversion material, such as uranium oxide or thorium oxide. One or more substrates form a micro-sized detection cavity that is filled with a detection gas. A voltage is provided across anode and cathode wires in the detection cavity. A neutron absorbed in the conversion material may release reaction products into the gas, causing ionization of the gas which then produces a current or voltage signal. The small detector volume minimizes energy deposition into the detection gas by competing particles such as gamma rays, fast electrons, and beta particles, and therefore minimizes false counts while retaining large signals from neutron interactions.

Apparatus include an atmospheric pressure glow discharge (APGD) analyte electrode defining an analyte discharge axis into an APGD volume, and a plurality of APGD counter electrodes having respective electrical discharge ends directed to the APGD volume, wherein the APGD analyte electrode and the APGD counter electrodes are configured to produce an APGD plasma in the APGD volume with a voltage difference between the APGD analyte electrode and one or more of the AGPD counter electrodes. An electrode can be integrated into an ion inlet. Apparatus can be configured to perform auto-ignition and/or provide multi-modal operation through selectively powering electrodes. Electrode holder devices are disclosed. Related methods are disclosed.

A fissile neutron detection system includes an ionizing thermal neutron detector arrangement including an inner peripheral shape that at least substantially surrounds a moderator region for detecting thermal neutrons that exit the moderator region but is at least generally transparent to the incident fissile neutrons. A moderator is disposed within the moderator region having lateral extents such that any given dimension that bisects the lateral extents includes a length that is greater than any thickness of the moderator arrangement transverse to the lateral extents. The moderator can include major widthwise and major lengthwise lateral extents such that any given dimension across the lengthwise and widthwise lateral extents includes a length that is greater than any thickness of the moderator arrangement transverse to the lateral extents.

A neutron position detector according to an embodiment includes a tubular enclosure used as a cathode, an anode located at an axial center inside the enclosure, and a gas that includes a .sup.3He gas and an additive gas and is sealed inside the enclosure. The additive gas includes nitrogen as a quenching gas, and argon as a gas that reduces the ranges of reaction products as neutron and .sup.3He gas.

A neutron position detector according to an embodiment includes a tubular enclosure used as a cathode, an anode located at an axial center inside the enclosure, and a gas that includes a .sup.3He gas and an additive gas and is sealed inside the enclosure. The additive gas includes nitrogen as a quenching gas, and argon as a gas that reduces the ranges of reaction products as neutron and .sup.3He gas.

A narrow thermal neutron detector includes a slidably receivable ionization thermal neutron detector module within an overall housing body. An active sheet layer of the ionization thermal neutron detector module can be tensioned across its width. The ionization thermal neutron detector module can include module upper major surface extents and module lower surface extents such that, when installed within the housing body, the module upper major surface extents are in a first spaced apart confronting relationship with housing upper major surface extents to define a first clearance and module lower major surface extents are in a second spaced apart confronting relationship with housing lower major surface extents to define a second clearance to accommodate housing flexing due to ambient pressure change. The housing body can be formed with a single opening for receiving the ionization thermal neutron detection module or with opposing first and second opposing end openings.