Spectrum Identification & Artifacts

Peak Identification

Continum X-Rays

White radiation(Continuum)

CharacteristicX-ray

EjectedElectron

Incident electron beam

Change in background slope due to increased charge during acquisition.

8 12keV

Bkg for a Conductor Actual

Bkg

The blue dashed background is for an insulator with an equilibrium charge. The red background shows a varying amount of charge.

Characteristic X-Rays

Depth of Excitation Electrons lose energy in steps as

they go deeper in the sample. The electron energy may drop below

the critical ionization energy of the element in the sample.

The ratio of the primary beam energy to the excitation of the element is referred to as the overvoltage.

X-Ray Absorption

x-rays

samplesurface

primarybeam

Area of absorption

The ratio of absorbed to emitted x-rays increases with the accelerating voltage.

X-Ray FluorescenceK Kab

Cr 5.41 5.988

Fe 6.39 7.11

Ni 7.47 8.33

What if there was Mn in this sample?

The Mn Kab is 6.53. Fe K can not excite MnK but Ni K would be able to fluoresce MnK

Comparison of window material X-ray transmission

Type B C N O F

ECON 100% 100% 100% 100% 100%

SUTW 25% 85% 42% 60% 70%

UTW 12% 42% 20% 30% 35%

BE 0% 0% 0% 0% 5%

A Be detector will not show any characteristic X-rays below about 0.75 keV. UTW and SUTW detectors will show peaks at these low energies but at a diminished peak height.

X-Ray Artifacts

Peak Broadening

Peak Distortion /Asymmetry

Escape Peaks Absorption

Edges

Silicon Internal Fluorescence Peak

Sum Peaks Stray Radiation A Warming

Detector

Peak Broadening

Peaks broaden as you increase in energy. Characteristic asymmetry of peak- high end of peak is sharp (the

absorption edge) while low end of peak tails due to possible incomplete charge collection.

Escape Peaks

SiLicrystal

Ca @

3.6

9

Si @ 1.74

1.74

1.95

Peaks with energies greater than 1.84 keV will create escape peaks. Higher energy peaks deposit energy deeper in the crystal and have a lesser chance of creating an escape peak because the Si X ray tends not to travel such a distance.

Warming Detector

As the detector warms the noise peak widens and may appear in the spectrum as a low-end noise peak. All peaks will broaden and may shift in energy

Ni-Cu K & L Series Peaks

Note the better separation of adjacent elements at higher energies. In manual ID, you should start with the higher energy peaks for this reason.

K-Series Peak with Sum and Escape Peaks

The Kb peak is about 1/8 the size of the Ka. The Kb becomes smaller and closer to the Ka at lower energies.

Tin- L-Series Peaks

Typical L-series peaks. A small Ln peak exists between the Ll and La. At lower energies, the peaks move closer together and are eventually not resolved.

Osmium- M Series Peaks

M-series peaks are similar to the L-series peaks at lower energies. Better separation of the peaks at higher energies is not achieved because the periodic table does not contain sufficiently high Z elements.

Stainless Steel Deconvolution

The peak fit is shown with the HPD function, the misfit of the Cr Kb results from the small presence of Mn Ka.

Optimization of X-Ray Count Throughput and Time Constant

Resolution-Time Constant Relation

At faster time constants, the throughput is increased but the resolution broadens. Fast time constants are commonly used for mapping but not for the collection of spectra with subtle overlaps.