Portable X-Ray
Fluorescence to Determine
the Composition of
Household Objects
Katherine Spoth, mentor Peter Revesz
August 13, 2010
The Project
• Learn the physics of XRF
• Master the use of the XRF setup
and related software
• Collect samples
• Run XRF measurements/collect
spectra from each sample
• Identify features in the spectrum
• Determine which element produced
each peak
• Use software to carry out rough
quantitative analysis
Review of XRF
• Incoming X-ray
radiation excites an
inner electron and
causes it to be
ejected from an atom.
• Outer electrons fall to
fill this vacancy,
releasing X-rays with
energy equal to the
difference between
the two energy levels.
Review of XRF
• Each element when excited emits a unique
X-ray spectrum.
• This is used to determine which elements
are present in a spectrum from an unknown
sample.
The characteristic spectrum of copper.
Setup
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Amptek Mini-X X-ray tube.
Generates X-rays by using accelerated electrons to
excite electrons in a silver target, which then emits Xrays at its characteristic energy 22.16 keV.
Continuous Bremsstrahlung radiation also produced.
Setup
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Amptek XR-100SDD - silicon drift detector
Amptek PX4 - digital pulse processor and multichannel
analyzer
X-rays create electron-hole pairs in silicon material in the
detector, produces electrical pulse with height proportional
to X-ray energy.
PX4 measures pulse height and sorts into channels based
on X-ray energy, producing a spectrum.
Setup
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The sample is placed on a joystick-controlled 2-axis table.
Allows user to change locations or look at multiple samples
without turning off the X-ray source and opening the
enclosure.
Setup
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Setup also includes a camera that allows the user to see where the
sample is located.
Can use a fluorescent screen to determine the area that the X-ray
beam impacts.
This can be marked onto the camera and used to determine which
part of the sample is receiving X-rays.
Allows view of a sample to be shown on a projector for
Setup
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X-ray source, sample, and detector all are contained in a lead
acrylic enclosure, ensuring no radiation can escape.
Interlock system prevents door from being opened while X-ray
source is powered on.
Spectrum Analysis
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The collected spectrum is displayed in Amptek’s ADMCA program.
The program is also used to control the PX4, to start and stop data
acquisition.
Spectrum Analysis
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Peaks can be selected and their centroid energy will be displayed
Determine which element produces a peak at that energy, look for
other peaks from the same element to be certain of its presence
Quantitative Analysis
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After it is determined which elements are present in a sample,
XRS-FP can be used to give approximate concentrations
This software processes the spectrum: removes background,
smoothes the spectrum, removes artifacts from the source,
subtracts a background spectrum, and deconvolves the spectrum
to compute the intensity of each element peak
Uses fundamental parameters to compute concentrations from
these intensities
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This approach requires the user to input details about the
geometry of the XRF setup and a list of the elements present
Quantitative Analysis
A spectrum before and after processing in XRS-FP.
Quantitative Analysis
Quantitative Analysis
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Method has several limitations:
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X-rays from light elements attenuate in air too much to be
detected by this setup
The mass fraction that is produced does not account for the
possible presence of light elements
Approximations in user inputs also decrease the accuracy of the
concentrations given by the program
These ideas need to be kept in mind when interpreting results from
XRS-FP.
Results
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Around 100 different samples were tested - very few were found
to contain anything harmful
Samples that did contain elements like lead and cadmium
tended to be older items
None of the samples we purchased for the project contained
dangerous materials (face paints, cosmetics, crayons)
Some interesting samples are shown on the following slides.
Results
This is a children’s bracelet that I found in my house, probably from
the late 1990s. The beads are colored made of colored plastic so
the lead found here is found in the beads, not just in a paint or
surface coating.
Results
The spectrum created by one sample of the face paint that was
purchased in June. The spectra shown have all been processed in
XRS-FP.
Results
This is the spectrum from the
green paint on this Pyrex mug
made in the 1970s.
Results
A soil sample collected near the
lower Wilson ab parking lot.
Outreach
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The portable XRF cart’s main purpose is outreach and teaching
Presented the setup to several groups of visiting teachers
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Gave brief introduction to XRF
Described the apparatus and setup
Demonstrated the process using a sample provided from the
audience
Allowed visitors to use the chart to match a peak’s energy to the
element
Outreach
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The XRF setup is a valuable teaching tool for several reasons:
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Its portability allows it to be used in any location.
Spectra can be displayed on the monitor on the cart or the computer
can be attached to a projector.
XRF can be easily explained to groups with almost any amount of
science background.
The use of audience-contributed samples increases interest and
participation.
Outreach
•
The XRF setup is a valuable teaching tool for several reasons:
•
•
•
•
Its portability allows it to be used in any location.
Spectra can be displayed on the monitor on the cart or the computer
can be attached to a projector.
XRF can be easily explained to groups with almost any amount of
science background.
The use of audience-contributed samples increases interest and
participation.