Prompt Gamma Neutron Activation Analysis of Niobium for Characterization of Light Interstitials

Graduation date: 2017High purity niobium metal is used in the construction of superconducting radio frequency (SRF) cavities in superconducting particle accelerators, such as the Large Hadron Collider (LHC) at CERN or the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. The usual method for characterizing the impurities in this niobium, the residual resistivity ratio (RRR) technique, can provide information relating to the superconducting quality of the material, and thus, a measure of the impurity content that is not specific to chemical elements. To improve the material quality further, another method must be used to specifically identify the elemental impurities at parts per million (ppm) levels. This study investigates the use of one potential method, Prompt Gamma Neutron Activation Analysis (PGNAA), for the application of high purity niobium metal, through the use of the PGNAA facility at the Oregon State University TRIGA ® Reactor (OSTR). Two “standard” samples were used to determine the response rate of the facility (in cps/g) for elements known as the light interstitials (H, C, N, and O), and five “unknown” samples were analyzed to determine the ability of the PGNAA technique to identify these impurities in a niobium matrix. The PGNAA technique shows promise for characterization of light interstitials in the material matrix of high purity niobium, as all PGNAA results reported are on the same order of magnitude as current chemical analysis results. For this analysis, the response rate of the PGNAA system that is associated with the “standard” sample that most closely conformed to the composition of the unknown samples was used. Additionally, the PGNAA results are well matched to the trends in the impurity values for carbon and nitrogen. With the use of a greater number of “standard” reference samples in future work, a far greater accuracy in the determination of detection limits and concentration values could be achieved