Status of (α,n)-Reaction Data for Nuclear Safeguards

Abstract: (α,n) reactions on light elements present an ubiquitous neutron source term throughout the nuclear fuel cycle. In some cases (α,n) neutrons may be used to quantify the mass of nuclear material, in some they provide screening information, while in other situations they are an interference. From a safeguards applications perspective it is important to be able to able to estimate the yield and spectrum of (α,n) neutrons. This paper briefly outlines the safeguards need and reviews the current status of (α,n) data commonly available for safeguards use. We identify a pressing need for new thick-target (α,n) yield data to support such applications and also to benchmark differential data which is needed in emission spectrum calculations. Direct thick target integrated over angle yield data, along with the largely independent associated activity technique when possible, provide a powerful approach to resolving the massive discrepancies present in the scientific literature and provide an unambiguous and accurate normalization at the 2% level for fundamental thin target data when used to construct thick target yield data for applications. New thin target (microscopic) data are also needed, particularly data on partial cross sections and angular distributions, since these are needed in the calculation of 4π emission spectra. We also note that α-particle stopping power data, which enters into the theory used to convert yield and spectra in one medium to a different medium, are flagged as an important contributor to the overall uncertainty, especially for actinide materials, and validation across a range of compounds is proposed. Finally the need and possibilities for updated tools and data archives are discussed.