Diffractometers Information

Diffractometers are used to measure crystal structure, grain size, texture, and/or residual stress of materials and compounds through the interaction of X-ray beams, gamma rays, electron beams, or neutron beams with a sample. Traditional diffractometers use X-rays, electromagnetic radiation with wavelengths in the range of 0.1 to 10 nanometers (nm). Typically, X-ray diffraction instruments are used to study the crystalline structure of solids and ionizing gases. Because X-rays are diffracted mainly by electron density, an analysis of diffraction angles can be used to produce an electron density map of a given crystalline structure. Crystals diffract X-rays passing through them at specific angles depending on the X-ray wavelength, the crystal orientation, and the structure of the crystal. 

There are several basic types of diffractometers. Electron diffractometers and neutron diffractometers are sensitive to nuclei. Often, these diffraction instruments are used to determine hydrogen positions with great accuracy. Because hydrogen atoms have a low electron density, determining their positions requires an extensive requirement of the diffraction pattern. Diffractometers include gamma ray devices, which use gamma radiation to examine the structure of crystals. X-ray, electron, neutron, and gamma ray diffractometers use detector types that are listed as camera or film, imaging plate or foil, position sensitive detector (PSD), solid-state or semiconductor, and scintillation.   

Diffractometers carry several product specifications for configuration. These include diffraction method, sample/detector positioning system, and diffracted beam optics. There are three main choices for diffraction method: Laue or single crystal, rotating crystal, and other methods such as Lang, Borman, or rocking curves. Choices for sample/detector positioning system include goniometer, Eulerian cradle, and transition stage. Diffracted beam optics are defined as monochromating crystal, collimators and slits, and K-beta absorption filter. Some diffractometers are benchtop devices. Others are handheld or portable products. Crystal orientation, crystal quality, and residual stress are additional factors to consider. 

There are four main performance specifications for diffractometers: angular rate, angular accuracy, peak count rage, and maximum specimen diameter. Angular range is the range of diffracted beam angles that can be measured. Angular accuracy, the resolution in diffracted angles, can be measured on a diffracted angle vs. intensity plot or diffraction pattern. Peak count rate is the maximum rate in counts per second (cps) produce by the substrate and measured by diffractometers. Maximum specimen diameter is the greatest sample width that diffractometers can measure.