The minimum wavelength of an x-ray occurs when all the energy of the accelerated electron is converted into an X-ray photon in a single collision. However, most of the accelerated electrons are stopped after a few collisions. Different electrons convert different amount of their kinetic energies into X-ray photons of different wavelengths, resulting in the continuous background spectrum.
Using an X-ray spectrometer and a crystal as a wavelength selector, the intensity of X-rays emitted as a function of its wavelength can be measured and then plotted.
|The X-ray spectrum.|
The X-ray spectrum consists of a continuous background of X-ray radiation and a series of characteristic lines with intensity peaks.
In the continuous background, the intensity varies smoothly with wavelength. The background intensity reaches a maximum value as the wavelength increases and then falls as the wavelength increases further.
The characteristic X-ray spectrum which consists of sharp peaks of high intensity occurs at specific wavelengths, unaffected by the voltage of the X-ray tube.
The peaks are a result of the electrons from the cathode knocking out inner shell electrons from the target atoms. When the vacant shells are refilled by free electrons, X-ray photons of specific wavelengths are emitted.
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|Painstakingly painted in MS Paint.|
The figures above show the mechanism behind the characteristic X-ray spectrum.
What's the K and L in the Graph? What do they stand for?
Until next time.