What is an X-Ray?
An X-Ray is an electromagnetic wave, it has a wavelength 0.001 to 10 nanometers which overlaps with gamma’s wavelength. However X-Rays are different from gamma as they are produced from fast electrons rapidly decelerating to produce photons of Electromagnetic Radiation.
Medical X-Rays are known as ‘soft’ as they are lower energy than gamma which is produced by radioactive substances. Medical X-Rays are produced in an X-Ray tube:
1. High energy electrons (100keV) are emitted from the filament cathode and accelerated towards the anode.
2. When the electrons hit the anode some energy (~1%) is converted into X-Rays
3. Some of the X-Rays can then pass through the window out of the vacuum as a collocated beam.
Most of the energy emitted from the electrons hitting the anode is converted to heat energy, this means the anode needs to have a high melting point so it can be used more frequently; Tungsten is often used due to this fact. Usually the anode is rotated so that it is kept cooler and can be used for longer.
Calculating the Wavelength
λ – Wavelength of X-Rays produced (m)
h – Planks constant (6.63×10 J s–1)
c – Speed of light in a vacuum (3×10 m)
e – Charge on an electron (1.6×10 coulombs)
V – The p.d. the electron is accelerated through.
Sometimes when the electrons hit the anode at high speeds, electrons at the anode get excited. When the electrons relax back to their normal energy level a photon is released, the energy of the photon is equal to the difference in the energy between the energy levels. Some elements are more prone to emit photons of energy than other elements and so will be characteristic to that element.