by Ron Kurtus (revised 20 September 2013)
There are three major ways that x-rays are produced or generated. The most common is the Bremsstrahlung process, where a high speed electron traveling in a material is slowed or stopped by the forces of an atom it encounters, thus emitting an x-ray.
Another method is K-shell emission, where a high energy electron knocks an electron from an inner orbit in an atom, and an x-ray is emitted with the replacement of that electron. The third method occurs in a synchrotron, which is a subatomic particle accelerator that creates high intensity x-rays used for nuclear studies.
Questions you may have include:
- What is the Bremsstrahlung process?
- What is K-shell emission?
- What is the Synchrotron method?
This lesson will answer those questions. Useful tool: Units Conversion
The most common method of creating or generating x-rays is by the Bremsstrahlung process, where high energy electrons collide with a metal target, usually made of an alloy of tungsten combined with rhenium or molybdenum. Bremsstrahlung is German for braking or decelerating radiation. The phenomenon was discovered by Nikola Tesla around 1890.
(See the Biography of Nikola Tesla for more information on him.)
The way the Bremsstrahlung process works is that when a high energy electron hits or passes near the nucleus of an atom such as tungsten, it makes a sudden deceleration and change in direction. This loss of kinetic energy is transferred into radiation energy in the form of x-rays.
Note the the dual nature of electromagnetic radiation states that an x-ray may also be a high energy photon. In other words, a burst of radiation can be considered equivalent to release of a photon.
Another method to create x-rays is through K-shell emission. In the Bohr model of the atom, the K-shell is the first shell or innermost shell of the atom. It is at the lowest energy state among the atom's shells.
When a high energy electron is accelerated into a metal target, some electrons knock the K-shell electrons out of orbit. An electron from a higher energy orbit or shell will jump down to replace the lost electron. Since the K-shell requires a lower state of energy, radiation energy is given in the form of an x-ray photon.
The explanation for K-shell x-ray emission using the electron cloud model of the atom is similar, although not as straightforward.
Since electrons are so very small compared with the nucleus of a moderately heavy metal atom, the probability of collision of an incoming electron with a K-shell electron is very small. This process is extremely inefficient in to producing a reasonable amount of x-rays.
A synchrotron is a large device used to study the effects of accelerating subatomic particles through high-powered magnetic fields at speeds near the speed of light. When electrons spiral around a magnetic field at high velocities, they give off radiation depending on their velocity. At high enough velocities, the radiation is in the form of x-rays. This is called synchrotron radiation.
Synchrotron radiation and a more simple cyclotron radiation are used as sources of x-rays primarily for laboratory nuclear studies.
Caused by change in velocity
Since velocity is speed in a specific direction, circular motion represents at change in velocity or acceleration (deceleration). When a charged particle such as an electron decelerates, it gives off electromagnetic radiation equivalent to the loss in energy from the deceleration. Thus, x-rays can be generated.
X-rays from Sun use same method
Since the Sun has extremely high energy electrons, as well as strong magnetic fields, it is a source of natural x-rays by the same synchrotron effect. The energy of those x-rays is greatly diminished by the time they get to the Earth.
The three major method to generate x-rays are the Bremsstrahlung process, K-shell emission and synchrotron radiation. In Bremsstrahlung process, a high speed electron traveling in a material is slowed or stopped by a nucleus, thus emitting an x-ray. In K-shell emission, a high energy electron knocks an electron from an inner orbit in an atom, and an x-ray is emitted with the replacement of that electron. In synchrotron radiation, electrons emit x-rays while spinning in a magnetic field.
Be courageous in what you do
Resources and references
Viewing the Periodic Table of the Elements with X-rays - College experiment using K-shell method
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