XRF User Guide




Hardware
X-ray Target - this is the source of your x-rays. In tube-based devices, this is your metal anode. In isotope devices, this is your radioactive isotope.
Voltage - this is the energy range of the photons you are sending in. Typically only the maximum is reported since the minimum is always 0.
Current - this is how many electrons are interacting with the x-ray target. These are typically reported in μA or mA depending on your device
Watts - this is voltage (keV) times current (μA) divided by 1,000. For example, analyzing at 40 keV with 30 μA would be a 1.2 watt draw on the tube.
Detector - this is the 'eye' that sees your photons - in portable instrumentation it is either a silicon pin diode or a silicon drift detector.
Channels - these are the units of detection in your detector. They receive and then amplify the photons returning from your sample.
Filter - an object which you put between the x-ray source and your sample to either a) attenuate the signal to allow for better signal-noise ratio of elements or b) preferentially exit an element
Atmosphere - this includes every atom between your sample and your detector. This includes dry air compositions (nitrogen, oxygen, etc.) and any other matter present (e.g. the window of your XRF if present).

Spectra
K-alpha peak - formed from photons emitted when an L-shell electron jumps to the K orbital.
K-beta peak - formed from photons emitted when an M-shell electron jumps into the K orbital, this peak will be higher in energy than the K-alpha line, but will be smaller.
L-alpha peak - formed from photons emitted when an M-shell electron jumps into the L orbital.
L-beta peak - formed from photons emitted when an N-shell electron jumps into the L orbital.

Rayleigh Peak - this is the elastic scatter that occurs within a sample, in XRF it will be the K and L lines for the element that composes the X-ray target. Typically this is rhodium, tungsten, molybdenum, or silver.
Compton Peak - this is the inelastic scatter that occurs within a sample, it will occur at both a slightly lower and slightly higher energy than the Rayleigh Peak. It has a wider gaussian distribution than any other peaks that is present.
Bragg Peak - this is coherent scattering that occurs within the sample when photons interact with the crystalline structure of a sample. To test if you have these peaks, rotate the sample slightly and retake the assay - the coherent scatter will shift in the spectrum.
Bremmsstrahlrung Radiation - this is commonly referred to as the backscatter in the spectrum. It is the result of outer electron shell transactions (often to the L or M shell) which create a continuum in the spectrum.

Sum peak - these occur when a single element dominates the signal in the spectrum. With sufficiently high count rates, the detector incorrectly assigns two photons of the same energy as one photon of double the energy.
Escape peak - these are the product of photons escaping from the detector, causing a fluorescence of the elements composing the detector. The lower energy photon that excited the atoms in the detector is then reabsorbed, with its energy minus the detector's energy. For silicon pin diode and silicon drift detectors, this peak will be present at the energy of an element minus 1.7 keV.

Resolution - your detector counts photons using channels, but your spectrum reports energy. Each channel has a set number of eV that it can represent. For silicon-drift detectors, this is typically 19 - 21 eV/ch, depending on the sample.
Energy Calibration - this is the mathematical formula used to convert channels into energy for the x-axis. This changes from sample to sample, and often is automatic. Some instruments require a manual calibration by shooting a standard first.
FWHM - this is the full width height maximum of the manganese K-alpha peak. For silicon-pin diode detectors it is around 200 eV, in silicone drift detectors it can be as low as 138 eV, but this depends on your instrument and sample.

Safety
Ionizing Radiation - this is the result of photons causing electron transitions in a sample or organism.
Hazard - this is the danger of a given photon to a given sample.
Exposure - this is the quantity of photons an organism is exposed to over a given period of time.
REM - the Roentgen Equivalent Man (REM) is a measure of the equivalent dose of ionizing radiation. One REM is equal to 0.01 sievert; in the United States any individual is limited to 5 REM lifetime ionizing radiation exposure.
Sievert - this is the standard derived unit for ionizing radiation dose; these represent the random health risk which accumulates with exposure to ionizing radiation.
Primary Beam - this is the direct, uninterrupted path of the x-rays generated by instrumentation. This is the primary risk of ionizing radiation exposure for most instruments.
Secondary Scatter - these are the elastically and inelastically reflected photons that have ionizing potential. These have the same hazard as the primary beam, but their is much lower exposure since many photons from the primary beam are absorbed by the sample.
Radiation Shield - this is an object that can sufficiently attenuate (absorb) all photons emitted from an instrument. There is no universal radiation shield - they are specific for each maximum energy of photons from the instrument.

Physical Concepts
Fluorescence Efficiency - the percentage of atoms that fluoresce. This happens because outer shell electrons shuffle around instead of inner shell electrons, resulting in energy balance.
Absorption Edge - this is the point at which there is maximum potential to eject an electron from an inner shell orbital of the atom - after it is a rapid drop to a 0% chance. You can think of the absorption edge as a normal distribution with the left half cut away.
Mass Attenuation - this is absorption of photons of a given energy as it passed through a medium like air or metal - think of it as the lost signal. These are calculated using the mass attenuation coefficient (-μ/ρ), where μ is the attenuation coefficient and ρ is the mass density. You can calculate μ here.

Quantification
Reference Standard - this is a sample with a known chemical composition that is employed in an empirical calibration on your instrument.
Calibration Curve - this is a linear/multilinear/nonlinear model formed with photon counts on the x-axis and concentrations on the y-axis used to estimate concentrations in a sample. It is generated using reference standards with known concentrations.
Empirical Calibration - this is a quantification protocol which is generated by measuring reference standards.
Fundamental Parameters - this is a mathematical technique which attempts standard-less quantification of multiple matrices
Deconvolution - this is a process by which net intensities for each elemental peak are estimated using physical parameters. This can be done using either a least-squares or Bayesian approach.
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