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Transmission geometry

PANalytical


X-ray techniques using transmission geometry

X-ray analytical techniques that make use of a transmission geometry require samples that are sufficiently transparent for the type of X-rays used. The incident X-ray beam fully penetrates, and is transmitted through, the sample with only moderate attenuation, typically by a factor of less than five to ten. Transmission techniques probe for the structure within the sample volume that is illuminated, e.g. by measuring the intensity of the diffracted beam as a function of the diffraction angle.

Samples to be measured in a transmission geometry may be confined e.g. between thin polymer foils or in a capillary, or mounted as free-standing objects. It is important to optimize the sample thickness for transmission measurements: whereas increasing the sample thickness results in a larger diffracting volume, the attenuation by the sample also increases. The right balance between these two effects must be determined.

A transmission geometry should be considered for samples that are:

  • Made of weakly absorbing materials; e.g. pharmaceutical substances, proteins, synthetic polymers (foils and fibers) and other organic materials
  • Fluids; e.g. liquid dispersions or slurries
  • Only available in very small amounts and that can be transferred in a thin capillary
  • Air-sensitive and can be sealed in a capillary or between thin polymer foils
  • Powder samples prone to preferred orientation effects (important for structure refinement studies); these could be measured in a spinning capillary
  • To be measured at very low angles; using low-angle diffraction or SAXS
  • To be investigated with respect to their bulk properties; e.g. XRD of a pharmaceutical tablet in a blister package

PANalytical solutions for transmission setups

The Empyrean and X'Pert³ Powder multipurpose X-ray diffraction platforms offer a wide range of X-ray analytical techniques that make use of a transmission geometry, such as:

PANalytical has developed a variety of sample stages and optical PreFIX modules specifically for transmission measurements. These include:

  • Capillary spinner
  • Low- and high-temperature options for capillary measurements
  • Reflection-transmission stage with sample spinner and automatic sample changer
  • SAXS/WAXS stage
  • The unique Slurry Flow Cell allowing in situ crystallization studies of organic (pharmaceutical) substances
  • Focusing and parallel beam X-ray mirrors, also for hard radiation (Ag and Mo)
  • CT stage

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