Berlin 2018 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 68: Poster: Complex Fluids, Glasses, Granular
DY 68.6: Poster
Thursday, March 15, 2018, 15:30–18:00, Poster A
Why beam hardening is necessary to measure volume fractions in granular packings — •Manuel Baur1, Norman Uhlmann2, Thorsten Pöschel1, and Matthias Schröter1 — 1MSS, FAU, Germany — 2Fraunhofer Institute for Integrated Circuits, Fürth, Germany
We study density waves in a fluidized bed via x-ray radiography. Dense regions in the bed attenuate the x-rays stronger than dilute ones and result in darker gray values. The commonly used Lambert-Beer law, to describe the photon attenuation, is just valid for monochromatic x-ray beams. Industrially used x-ray tubes do not emit a monochromatic beam, but the broad Bremsstrahlung spectrum. In this case the attenuation coefficient depends on the photon energy. High energy photons are attenuated less than weak energy photons. The ratio of high to low energy photons in the spectrum of the x-ray beam increases after transmitting a slab of material - the beam hardens. An understanding of beam hardening is necessary to quantize density fluctuations in a fluidized bed from radiograms. We present a technique to access the x-ray attenuation as a function of transmitted material thickness and show how the transmitted thickness can be deduced from that.