4. 1 DESCRIPTION.

4. 1. 1 In-Core Detector Assemblies

The in-core detector assemblies are designed for operation within power reactor cores in either a water or air ambience. Both the in-core Campbeller and the counter assemblies consist of a detector enclosure which has a 1/4-inch o. d. x 2-5/8-inch length, a 3/16-inch-o. d. radiation — and temperature-resistant cable, and a ceramic-to-metal cable seal termination. An adapter is mounted on the cable seal which mates with a standard HN connector. • Only Type-304 stainless steel is exposed to the reactor ambience. All exposed joints are inert-arc-welded.

The detectors proper are integral units 0. 160 o. d. x 1-3/4 inches long, contained within the detector enclosure of the probe. Chamber materials are titanium, fosterite ceramic, and argon filling gas. A uranium coating is electro-deposited on the inside diameter of the chamber shell. Careful attention is given to the outgassing and backfilling processes to prevent impurity contamination of the fill gas. All materials and processes used in the fabrication of these devices are similar to those used in the ceramic-metal electronic tube industry. The Campbell chamber differs from the counter in that the gas pressure-gap length product is smaller, and the chamber contains less uranium. . •

The coaxial cable consists of a Type-304 stainless steel center conductor, quartz fiber insulation, a stainless steel braid, a double braid of copper, and a Type-304 stainless steel sheath tube. The materials used in the cable were chosen to meet the requirements of signal transmission, physical compatibility, and tolerance to elevated temperature and radiation levels.

An HN type termination for the cable connector provides a high-quality, moisture-proof. connection to the interconnecting cable.

4. 1.2 Out-of-Core Detectors.

The out-of-core detector used in the tests was a standard General Electric fission counter, NA04, constructed mainly of aluminum and alumina ceramic. The argon gas gap length is 1/8 inch. External dimensions are 3 o. d, x 13-1/2 length. An HN termination providёs con­nection to the standard cable. Both the inner and outer surfaces of the active volume are coated with uranium.

A brief description of the pulse formation process in a fission ion chamber is contained in the following paragraphs of this section.