Lab 3: X-ray Fluorescence (XRF)
This lab contains:
- Introduction to XRF
- XRF theory
- XRF analysis procedure
- Lab 3: XRF Worksheet
X-ray fluorescence (XRF) has been used for over fifty years to investigate the composition of cultural, scientific, archaeological and historic objects. This technique is non-destructive and can be used in situ—in the place where it was found—which makes it suitable for fieldwork. XRF is a very valuable tool for elemental analysis, but it does not quantify (how much) the elements in the object tested. The XRF technique is qualitative (is it present) and is valuable for establishing elemental signatures which can illuminate the object’s origin. One case in point is the origin of copper tools in the Americas. Copper from the Great Lakes region of North America is found in tools used by the Caddo Indians in Northwest Louisiana. With this information, it is possible to deduce that trading occurred from Canada to the Gulf of Mexico in Pre-Historic times.
The physical principles of XRF are quite simple and well established. Electrons located in the atom’s inner shells (K, L, and M) are excited by electromagnetic radiation. This results in vacancies in the atoms of the surface layers. These vacancies de-excite by the production of a secondary (fluorescence) X-ray whose energies are unique to a specific element. Each element has a characteristic signature that can be used to identify itself. In other words, X-rays bombard the sample surface and send the electrons to a different energy level. When the electrons transition back into their respective orbits, they emit X-rays (fluorescence). The resulting energies are plotted and a spectrum of the sample is produce. The XRF unit that NCPTT has is the Tracer III-V (figure 4).
XRF Analysis Procedure
- Refer to Figure 4 to recognized XRF instrument.
- The XRF and the computer will be setup already and the first step is as follows:
- Double-click on the icon named “S1PXRF”
- Turn XRF on with key switch
- On the top menu, select ‘Download’
- From the ‘Download’ submenu, select ‘Port’
- From the ‘Port’ submenu, select ‘Com1’
- Now click ‘OK’
- The screen changes and a command button called ‘Timed’ is visible
- Click the ‘Timed’ command button and select ‘Timed Assay’
- There are several parameters that appear
- Change ‘Test Time’ to 60 seconds
- The ‘FWHM’ parameter must be 220
- Under ‘File Types’, make sure that all file types are checked
- Close the screen by clicking ‘OK’
- At this time, a ‘Save’ dialog box appears
- Navigate if needed to the proper directory and type in a file name
- The file naming convention is:
- **DO NOT CLICK SAVE YET**
- Make sure there is XRF film covering the sample platform
- Place the specimen on the sample platform and now click ‘Save’
- A graph of the elemental composition will appear
- Reviewing results:
- Once the results are visible, a command button called ‘Elem’ will appear
- Click this button and a screen will appear. This screen is similar to the periodic chart of elements. It also lists the K, L, and M shells.
- For example, if the ‘Pb’ command button is clicked, the peak for lead (Pb) will be highlighted with a blue line. If you want to annotate the peak, click the ‘Add” command button.
- Repeat the last step for each element that may be in the sample
- Record any and all results on the XRF Worksheet
- The file saves automatically and you may print the graph also
- Remove the sample from the sample platform and clean the area
- As soon as all the XRF scans are complete, an NCPTT staff member will print them and disperse the results to each respective group
At this time please refer to Lab 3: XRF Worksheet below.
Rubric for “Conservation Scientist for a Day”
Task: You are working in a team of conservation scientists collaborating to identify the composition of a recently found pottery shard. You are expected to describe the physical characteristics of the object and document it. You are expected to use chemical methods to identify some of the elements found in the glaze of the pottery. You will observe the body of the pottery shard and describe what you see under a microscope. Once you complete the exercise, each team member will work with the information to create a report on the object. The report will have an introduction, a description of the experiments, a presentation of data, an interpretation of data, and a conclusion.
The recommended grading is as follows:
|Object Characterization||All Sections of the description worksheet are complete. Written description is accurate and detailed.
|Most sections of the description worksheet are complete. Written description is accurate but lacks detail.
|Sections of the description sheet are not completed. Detail and accuracy are not identified in the description.||20 points total|
|Participate in hands-on experiments, accurately follow instructions and complete all tasks. Provide accurate information about the object.||Participate in hands-on experiments, follow instructions and complete most tasks. Provide mostly accurate information about the object.
|Fail to complete hands-on experiments. Have trouble following instructions. Record inaccurate information.||20 points total|
|Interpreting Data||Carefully consider data in your written report; provide accurate information about the artifact; and use data in your interpretation of the elements present in the object in your conclusion.||Mostly consider data in your written report; provide mostly accurate information about the artifact; and relate most data to written conclusions.
|Interpretation/evaluation of team data is not evident in their written report. Jumps to conclusions without carefully considering the data.||20 points total|
|Disseminating Information||Written report contains all sections. Information is presented in an orderly fashion. Information is accurate.
Data supports conclusions.
|Written report contains all sections. Information is mostly accurate.
Data supports conclusions.
|Not all sections of written report are completed. Facts don’t support conclusions. Information is inaccurate.
|20 points total|
|Contribute to the team; treat each other with respect and kindness; and complete all the tasks.
|Make an effort to contribute to the team. Complete some tasks.||Work separately from the team; ideas of others are not respected; tasks are not completed.||20 points total|