Cobalt and silver nanocoatings for reactor dosimetry

Activation foils are an important tool for the characterization of neutron fields. Some of the materials that are used in these foils have large interaction cross-sections that cause unwanted self-shielding effects. In practice experimenters minimize these effects by using aluminium alloys. An alternative approach can be a nanocoating of a pure material on a carrier. The validity of this approach is investigated in this work. Nanocoatings can be more flexible compared to alloys and can probably reduce the number of required post-irradiation gamma spectrometry measurements. Cobalt and silver nanocoatings were deposited by physical vapour deposition on nickel and aluminium carrier foils. The nanocoatings were tested in two irradiation campaigns in the Belgian Reactor 1 at SCK CEN. By depositing nanocoatings with different thickness and determining the corresponding number of activated atoms the inherent flexibility of the technique is demonstrated. When the dosimeters were punched from the carrier foils, the metal cylindrical punch damaged the nanocoatings which increased the spread on the number of atoms between different dosimeters. This is prevented by including a Ti interlayer of 5 nm between the carrier and the cobalt and silver layers. It was shown that this results in a coating with good homogeneity or minimal spread. This study shows that applying nanocoatings on a carrier is a valid technique to make dosimeters.