How to Calculate X-Ray Energy

••• x-ray image by Claudio Calcagno from

X-rays are a part of the electromagnetic spectrum, with a wavelength from 0.01 to 10 nm. Sources of X-ray radiation are used in crystallography to determine the three-dimensional structure of compounds. X-ray machines are also used in medicine diagnostics (radiography). X-ray sources typically have monochromators to produce radiation with a single wavelength. The energy of an X-ray is reversely proportional to its wavelength and is calculated by the equation \"E=hc/lambda\", where h is Planck constant, c is speed of light and lambda is the wavelength. X-ray energy is typically given in electronvolts (eV).

    Retrieve the values of the fundamental constants h and c (see References): Speed of light c =299792458 m/s Planck constant h =4.1356673310 10**(?15) eV s

    Calculate production of the two fundamental constants h and c. hc =299792458 (m/s) * 4.1356673310 10(?15) eV s=1.2398418746 10(?6) eV m

    Convert wavelength typically given in nanometers (nm) into meters (m) lambda(m)=lambda(nm) 10*(-9).

    Calculate X-ray energy in eV.

    E(eV)=hc/ lambda(m) E(eV) = 1.2398418746 10(?6) (eV m)/ (lambda(nm) 10(-9))= 1239.8418746 / lambda(nm).

    Example: if lambda is 0.15 nm then E=1239.8418746/0.15=8265.612497eV


    • If you obtain the X-ray wavelength in nm, go directly to Step 4.


  • “CODATA recommended values of the fundamental physical constants: 2006”, P.J. Mohr, B.N. Taylor and D.B. Newell, J. Phys. Chem. Ref. Data , V. 37, pp.1187-1284, 2008.

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