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Analysis of soils by X-ray fluorescence spectrometry (XFS) (CAT#: STEM-ST-0188-WXH)

Introduction

Portable X-ray fluorescence (PXRF) spectrometry is a proximal sensing technique whereby low-power X-rays are used to make elemental determinations in soils. The technique is rapid, portable, and provides multi-elemental analysis with results generally comparable to traditional laboratory-based techniques. Elemental data from PXRF can then be either used directly for soil parameter assessment (e.g., total Ca, total Fe) or as a proxy for predicting other soil parameters of interest (e.g., soil cation-exchange capacity [CEC], soil reaction, soil salinity) via simple or multiple linear regression. Importantly, PXRF does have some limitations that must be considered in the context of soil analysis. Those notwithstanding, PXRF has proven effective in numerous, agronomic, pedological, and environmental quality assessment applications.




Principle

XRF describes the process where some high-energy radiation excites atoms by shooting out electrons from the innermost orbitals. When the atom relaxes, that is, when outer electrons fill inner shells, X-Ray fluorescence radiation is emitted.

Applications

XRF is widely used as a fast characterization tool in many analytical labs across the world, for applications as diverse as metallurgy, forensics, polymers, electronics, archaeology, environmental analysis, geology and mining.

Procedure

1. Primary X-rays knock out an electron from one of the orbitals surrounding the nucleus within an atom of the material.
2. A hole is produced in the orbital, resulting in a high energy, unstable configuration for the atom.
3. To restore equilibrium, an electron from a higher energy, outer orbital falls into the hole. Since this is a lower energy position, the excess energy is emitted in the form of fluorescent X-rays.
The energy difference between the expelled and replacement electrons is characteristic of the element atom in which the fluorescence process is occurring – thus, the energy of the emitted fluorescent X-ray is directly linked to a specific element being analyzed.

Materials

XRF spectrometer (including X-ray source, sample chamber, analysing crystal, detector and signal processing computer)