First, A lesson in Fluorescence
What is XRF? Well it is X-Ray Fluorescense of course. The next obvious question is “What is fluorescence?”. When high-energy, primary X-ray photons (such as those emitted from the XRF analyzer’s x-ray tube) strike a sample, the electrons of the innermost K or L orbits are displaced and become unstable ions. Electrons seek stability, therefore this results in an electron from an outer L or M orbit to shift into the vacant space at the inner orbital. The electron moving from the outer orbital into the inner orbital causes a secondary X-ray photon to be emitted. This is known as fluorescence.
Individual elements produce their own characteristic secondary X-rays, which means they fluoresce differently than other elements. The energy (E) of the emitted fluorescent X-ray photon is determined by the difference in energies between the initial and final orbit of the transitions. The XRF can then measure these energy signatures and frequencies and determine the concentrations of specific elements and alloys in the sample. Simple enough, right?
Applications of XRF technology
When an X-Ray Fluoroscope or XRF is used properly it can confirm the absence or presence of specific elemental metals and alloys in soils, paint, and a variety of other materials. The technology of hand-held XRF and field portable analyzers allows the end user the ability to gather screening level to laboratory grade data at measurable concentrations and detection limits. Therefore the applications where XRF technology can be applied are tremendous. Manufacturers of XRF analyzers have developed instruments to benefit a wide variety of market places including many environmental applications. One benefit to the end user is that the handheld XRF analyzers can be used to analyze samples insitu, or with minimal transportion, alteration, or damage, making them an ideal field tool.
XRF analyzers of the past required the instrument to contain a hazardous radioactive source, requiring extra safety requirements and restrictive regulation. Modern XRF units do not contain radioactive material. The instrument generates and emits X-rays only when the X-ray tube is energized and taking readings. Although the modern, XRF analyzers are much safer than the older models, one must still be aware of the safety requirements. The instrument still emits X-ray energy and should never be pointed at anyone. It is important to follow all of the safety recommendations in the operator’s manual.
When using and XRF for environmental applications, it is imprtant to be aware of the accepted methodology for various applications. It is important to follow the workplan set forth in your scope of services and if the workplan states that work will be performed in accordance with a regulator approved protocol, please make sure you fully understand the methodology. Below is a list of some of the excepted regulator developed methodologies.
US EPA: Comply with Method 6200 for Metals in Soil; 8 RCRA (Cr, As, Pb, Hg, Se, Ag, Cd, Ba) & Priority Pollutant (Tl, Cu, Ni, Sb, Zn) Metals; CCA in Pressure Treated Woods http://www.epa.gov/waste/hazard/testmethods/sw846/pdfs/6200.pdf
US OSHA: Comply with Methods OSSA1 & OSS1 for Pb in Air Filters & Dust Wipes
US NIOSH: Comply with Method 7702 for Pb in Air Filters
EU RoHS: Screen for RoHS (Restriction of Hazardous Substances) Compliance for Pb, Hg, Cr, Br, and Cd
EU WEEE: Screen for WEEE (Waste Electrical and Electronic Equipment) Directive Identification of RoHS elements, in particular Hg, Cl, and other toxic metals
Understanding X-Rays and XRF Safety
Pine Environmental Services, Inc. does not intend this article to be a substitute for fully comprehending the risks and safety precautions associated with use of XRF analyzers.
X-radiation (composed of X-rays) is a form of electromagnetic radiation. X-rays have a wavelength of 10 to 0.01 nanometers, with frequencies in the range 30 petahertz to 30 exahertz (30×1015Hz to 30×1018Hz). X-ray energies are in the range 120 eV to 120 keV and are longer than gamma rays but shorter than UV rays.
The rem is the traditional unit of dose equivalent. This describes the energy delivered by X-radiation (indirectly ionizing radiation) for humans. The SI (International System of Units) counterpart is the sievert (Sv). One sievert is equal to100 rem. Because the rem is a relatively large unit, X-rays are typically measured in millirem (mrem), or in microsievert (μSv).
1 rem = 1000 mrem 1 Sv = 100 rem 1 μSv = 1/1000000 Sv 1 mrem = 10 μSv
The average person living in the United States is exposed to approximately 150 mrem annually from background sources alone. Dental X-rays dosage reports seem to vary significantly. Depending on the x-ray source, a typical dental X-ray results in an exposure varying from 3 to 900 mrems (30 to 9,000 μSv) with common medical and/or dental x-rays: 20-30 mrem each. Mammogram exposure is measured between 100-200 mrem, flying in a commercial jet coast to coast (6 hrs.) has exposures between 1-2 mrem, and daily exposure from background radiation measures between 0.3 to 0.5 mrem/day (depends on geographic location)
A single case of XRF analyzer misuse may issue a measured dose between70-250 mrem however, regular misuse, such as taking safety shortcuts, produces radiation exposure that greatly exceeds these typical levels and should be avoided entirely.
XRF Tips
• Familiarize yourself with the XRF analyzer prior to field operation. This saves time during sampling.
• When using the handheld or field portable XRF analyzers in accordance with USEPA Method 6200, become familiar with procedures outlined in the method to ensure compliance and optimum results.
• Instead of recording readings with only date time and sample number, customize data entry with dropdowns and detailed information about each sample.
• A fully charged XRF battery will last approximately 4 hours (Pine includes 2 batteries with rental). Pleaese be sure that both batteries are charged before sampling. Please request an additional battery if you anticipate longer work days.
• Use the soil or paint chip standards to confirm XRF accuracy and comply with QA/QC protocols.
• Be familiar with XRF safety and your state’s XRF safety regulations.
Link to the NRC: Federal & State Materials & Environmental Management website: http://nrc-stp.ornl.gov/asdirectory.html
Please call your local Pine office with any questions or concerns.
Pine Environmental Services, Inc.