WEric Landström: Material Identification using Multiple X-Ray Absorptiometry

Dual Energy X-ray Absorptiometry is a proven technique used to identify unknown materials, by measuring the transmission of two X-ray energies. This technique is limited to measuring a single chemical quantity and is not able to handle more chemical variation. To overcome this, one approach is to use multiple-energies to resolve more information. The differences in the processes controlling the X-ray transmission limits the theoretical resolution capability to three characteristics. Of these three, one is dependent on the sample geometry and density. The remaining two are purely chemical characteristics and are investigated in this thesis. It is found that using X-ray photon energies in the range 20-90 keV, it is possible to measure one chemical characteristic to a high precision. Two chemical characteristics can be measured in limited circumstances and even though the precision is good, the measurement is prone to inaccuracies in machine modeling and stability. A two step method is defined, first finding an approximation of the X-ray spectra and then reconstructing the attenuation coefficient of the sample to a high precision (< 0.2%) using a robust low-rank basis for the characteristics.