Preparation of thin-film neutron converter foils for imaging detectors

With the pending delivery of the new Spallation Neutron Source at Oak Ridge National Laboratory, a new generation of highly efficient, position sensitive neutron detectors needs to be developed. One promising prospect for detector development has been the neutron imaging detector, consisting of a conversion foil which produce amongst other things α and γ particles from incident neutrons, and a position sensitive charge particle detector. Historically the conversion efficiency has been low in these foils. To enhance the conversion efficiency, foils consisting of multiple converters and complex geometries need to be developed. In order to understand the materials chemistry between multiple converters as well as to maximize the production and transmission of the daughter products, we have prepared and characterized a series of thin-films from naturally occurring isotopes of the strong neutron absorbers Li, B and Gd. The films have been created using a combination of sputtering and evaporation techniques. The composition of the resulting films have been investigated using EDS and RBS while the interfacial mixing between the layers has been studied using a combination of RBS and SEM experiments. Experiments studying the aging of the detector films in the detector gas as well as alloying of Li and the film substrate have also been undertaken and the results are reported here.