Unidentified peaks in I-125 spectrum

May 30th, 2018
by Joseph Magill

Qu. (from Z. S. JRC Karlsruhe) Using the Gamma Spectrum Generator app in Nucleonica I have created a gamma spectrum for I-125 (shown below). Comparing the results from the Nuclide Datasheets++, I find the three lines at approx. 35, 31, 27 keV (see inset from the Datasheets++). Where do the extra peaks at approx. 21 and 17 keV come from?
UnPeaksAns. (Nucleonica Team)
The additional lines from the I-125 spectrum are X-escape peaks.

Ge emits X-rays at approx. 10 keV (Intensity 48%), 11 keV (intensity 6%), and about 1.2 keV (Intensity 0.5%) so Xesc-peaks can be expected at:
21 keV = 31 keV – 10 keV
20 keV = 31 keV – 11 keV and 21 -1.2

17.6 keV = 27.5 – 10 keV
16.5 keV = 27.5 – 11 keV and 17.6 – 1.2

25.4 keV = 27.5 -1.2 keV
The relative intensities correspond about to the relative Ge X-ray intensities.
More information:
X-Ray Emission Lines
X-ray Escape Peaks

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