Thoriated glass lenses—sometimes used in vintage cameras to reduce chromatic aberration—may contain up to 30% Th-232 by mass. For this analysis of Th-232, the Radiacode will rely on gamma emissions from its decay products, with a focus on the 238.6 keV peak produced by Pb-212, as well as the 583 keV and 2614 keV peaks produced by Tl-208.
Steps for Calibration:
1. Power on the Radiacode device.
2. Open the Radiacode application on your mobile device and connect to the Radiacode.
3. Turn off the sound to avoid triggering alarms.
4. Place the thoriated glass specimen over the trifoil symbol or beneath the plus sign located at the end of the Radiacode.
5. Reset the spectrum on the application by touching the three dots on the right side of the spectrum and selecting “Restart Accumulation.”
6. Allow the Radiacode device to collect sufficient data. Data collection is complete when the spectrum graph appears filled in with yellow past the 2614 keV line. This should take at least five hours with a thoriated glass specimen measuring 6000 CPM on the Radiacode 103.
7. Once enough data is collected, save the spectrum by pressing the three dots on the right side of the spectrum and selecting “Save Spectrum to Library.” Then, touch the three dots again and select “Energy Scale Calibration.” A blue overlay will appear at the top.
8. Indicate the first peak (point one) on the graph near 238.6 keV by touching it.
9. Enter the value 239 and touch “Next.”
10. Indicate the second peak for point two near 583 keV by touching it.
11. Enter the value 583 and touch “Next.”
12. Indicate the third peak and enter the value 2614, then touch “Finish.”
13. Touch “Save Coefficients” and then “Program Coefficients into Device.”
14. The calibration is now complete.
Calibration and Spectrum Adjustments for the Radiacode Device
If a mistake is made during calibration, you can undo the calibration and revert to the factory calibration by pressing the virtual button “Reset to Factory Settings.”
Energy Levels for Calibration
These instructions are not exclusive. Any three of the following energy levels may be used in ascending order as long as you can distinguish their peaks: 239, 338, 727, 911, 1588, and 2614 keV.
Historical Spectrum Adjustments
After calibration, you can adjust previous library spectra to match the latest calibration. To do this:
Open the Spectrum tab.
Tap the folder symbol on the toolbar to open the library.
Select the spectrum you want to adjust by tapping on it.
Tap “Edit Calibration Coefficients.”
Press “Copy from the Device”—the spectrum will then be adjusted to the new calibration.
Single-Point Calibration
To verify the calibration using normal background radiation or perform a single-point calibration:
Run a new spectrum for 36 to 48 hours by pressing the three dots and selecting “Restart Accumulation.”
Note: A previously saved spectrum cannot be used for this method. The spectrum must be actively running in the Spectrum tab.
After collecting enough data, a K-40 peak at 1461 keV (1460.8 keV) from natural potassium should be visible.
If the K-40 peak does not align at 1461 keV, perform a single-point calibration:
Open the settings in the Spectrum tab by tapping the cogwheel symbol.
Scroll down to “Calibration Coefficients.”
Adjust the a1 coefficient by ±0.05 units until the K-40 peak aligns correctly at 1461 keV.
Press “Save,” and it will return to the Settings page. Press “Save” again to save the calibration to the device. The single-point calibration is now complete.
Final Thoughts
Once calibration is complete, your Radiacode device will provide more accurate energy readings, improving gamma emission identification from radioactive materials. Using thoriated glass as a calibration source ensures a consistent and reliable method for energy scale adjustments. Regular calibration is recommended, especially if the device is exposed to varying environmental conditions.