Abstract: This neutron detector device includes a containment inside of which there is mounted a detector and which contains a neutral gas. The detector is formed by a fission type chamber comprising a cylindrical-shaped external electrode, coated with a lining of uranium in metal form, enriched as isotope 235, and a cylindrical-shaped internal electrode coaxial to the external electrode. The containment is of annular shape and arranges a cylindrical center space open at both ends to house a moderator to slow down the fast neutrons with great efficiency with respect to detection. The present invention provides an advantage of making it easy to replace the moderator. It is favorable to use cylindrical electrodes of large diameter thus increasing the sensitivity.

Abstract: A neutron detection device is housed in a metal enclosure containing a first detector with a high-sensitivity fission chamber, and a second detector having a low-sensitivity fission chamber and a boron-lined ionization chamber compensated for gamma radiation. The detection device is useful for extended range measurement of the neutron fluence rate outside the core of a nuclear reactor.