Moseley's Law
Definition
The square root of the characteristic X-ray frequency varies linearly with atomic number Z. Discovered by Henry Moseley in 1913, it is what turns an X-ray emission spectrum into an elemental identification rather than a guess. Lets a spectrometer assign every line to a Z value with confidence.
- Discovered by
- Henry Moseley
- Year
- 1913
- Relationship
- sqrt(X-ray frequency) is linear in atomic number Z
- Field
- X-ray spectroscopy (XRF, XRD)
- Forensic use
- Converts spectral lines into elemental identification
Common questions
Why was Moseley's law significant for the periodic table?+
It gave a physical, measurable definition of atomic number distinct from atomic mass, resolving ordering discrepancies in the periodic table of the time and confirming that elements should be arranged by proton count rather than mass alone.
How does this law get used in a forensic XRF measurement?+
An XRF spectrometer records characteristic X-ray emission lines from a sample, and the instrument's software applies Moseley's relationship to convert each line's energy or frequency into an atomic number, letting the analyst read off which elements are present in gunshot residue, glass, paint, or metal evidence.
Does Moseley's law give quantitative concentration, or just presence of an element?+
The law itself only identifies which elements are present from their characteristic line positions; determining how much of each element is present requires comparing peak intensities against calibration standards, a separate quantitative step in XRF analysis.
Related terms
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- ICDD PDF-4
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