Presented by: Scott Speakman Ph.D - XRD Principal Scientist
Modern laboratory diffractometers are designed to operate with X-ray tubes that may have many different types of anodes: Cr, Mn, Fe, Co, Cu, Mo, Ag, and more. The X-ray tube anode determines the wavelength of radiation that is produced for measurements. Despite the wide selection of anodes available, contemporary literature is dominated by research that uses Cu wavelength X-rays for powder diffraction and scattering studies—so much so that some researchers mistakenly believe it is the only choice because "everybody else uses it". While Cu anode X-ray tubes have always been widely used in laboratory diffractometers, literature provides many examples of measurements that benefited from the use of other wavelengths of radiation, including synchrotrons and neutron beamlines.
Selection of the X-ray anode can determine if the X-ray beam penetrates 4 microns or 100 microns into the sample, greatly influencing the irradiated volume and grain statistics that are important for quantitative phase analysis and texture analysis. Selection of the X-ray anode can optimize peak intensity and background noise. Selection of the X-ray anode can enhance sensitivity to certain dopants in an alloy or impurities in a mixture. Selection of the X-ray anode can determine the precision of large d-spacing and line profile analysis, such as hydration analysis in clays.
This presentation will provide historical context for the dominance of Cu anode X-ray tubes, will summarize the important considerations when selecting an X-ray tube, and will provide examples of research that benefited from using various wavelengths of radiation. Particular focus will be paid to hard radiation X-ray sources, such as Mo and Ag anode tubes, which can be used much more efficiently with the introduction of new CdTe based detector technology. Availability of a fast CdTe-based hybrid pixel area array detector that is highly efficient for hard radiation will improve classic analyses, such as retained austenite and residual stress analysis of steels, while also opening up the possibility of beamline-type measurements such as transmission texture and residual stress analysis through metal foils.
Scott A Speakman Ph.D - XRD Principal Scientist
Dr. Scott Speakman joined PANalytical as Principal Scientist in 2014. Prior to joining PANalytical, Dr. Speakman managed the X-ray Shared Experimental Facility at MIT for 8 years. Dr. Speakman earned his PhD from Alfred University, where he worked with Prof. Scott Misture on <i>in situ</i> X-ray diffraction analysis of ionic conductors for solid oxide fuel cells. He also was a post-doctoral research associate with the Diffraction and Thermophysical Properties group at Oak Ridge National Lab. Dr. Speakman is a Fellow of the International Center for Diffraction Data, the chairperson for the ICDD subcommittee on Micro- and Meso-Porous Materials, and was awarded a 2013 Infinite Mile Award for extraordinary service to MIT.