4 X-ray Production v2
Content
X-Ray Production
X-ray Production
Characteristic
One of the mechanisms for production of X-rays is when a
fast moving electron (same as a Beta particle) collides with
an electron in an inner shell and has enough energy to eject
it from the atom. An electron from an outer shell then ‘drops
down’ to fill the space and in so doing emits an X-ray photon.
The energy of these photons is determined by the difference
in energy levels of the shells. They are known as
characteristic X-rays and can be used to identify the target
material. However in the design of an X-ray set you may not
want these characteristic x-rays and need to include filters
that absorb them.
When an electron moves through an atom it is affected by
the electromagnetic fields. This causes it to slow down and
the loss of energy of the electron is in the form of photons,
known as bremsstrahlung (German for braking radiation) or
X-rays.
X-ray Production
Bremsstrahlung
The photons can have a range of energies up to the maximum energy of the incident electrons; forming an
X-ray spectrum as shown below. Superimposed on this are
the spikes from the characteristic X-rays.
The process of bremsstrahlung production is the
same, irrespective of whether the electron has been
accelerated by a high voltage (as in an X-ray set), or
beta particle from a radioactive source.
The figure on the right shows the basic elements of an
X-ray tube. In a vacuum, inside a glass envelope,
electrons from a heated filament are accelerated by a
high voltage. The stream of high energy electrons is
focused onto a small spot on a target. Often the target is
tungsten, because of its properties of high melting point
and high density. A high proportion of the energy in the
electron beam is transferred as heat and the target has
to have an efficient means of dissipating the heat.
X-rays are produced in all directions and the tube has to
have a shield. Through a port, a beam of radiation is produced. This goes through filters to reduce the unwanted
energies and produce a useful beam for radiography.
X-rays can also be produced by a radioactive process
called Electron Capture, where the nucleus absorbs
an electron from an inner shell and X-rays are then
produced when an electron from an outer shell ‘drops
down’ to fill the space. Iron-55 is an example.
X-ray Production
Characteristic
One of the mechanisms for production of X-rays is when a
fast moving electron (same as a Beta particle) collides with
an electron in an inner shell and has enough energy to eject
it from the atom. An electron from an outer shell then ‘drops
down’ to fill the space and in so doing emits an X-ray photon.
The energy of these photons is determined by the difference
in energy levels of the shells. They are known as
characteristic X-rays and can be used to identify the target
material. However in the design of an X-ray set you may not
want these characteristic x-rays and need to include filters
that absorb them.
When an electron moves through an atom it is affected by
the electromagnetic fields. This causes it to slow down and
the loss of energy of the electron is in the form of photons,
known as bremsstrahlung (German for braking radiation) or
X-rays.
X-ray Production
Bremsstrahlung
The photons can have a range of energies up to the maximum energy of the incident electrons; forming an
X-ray spectrum as shown below. Superimposed on this are
the spikes from the characteristic X-rays.
The process of bremsstrahlung production is the
same, irrespective of whether the electron has been
accelerated by a high voltage (as in an X-ray set), or
beta particle from a radioactive source.
The figure on the right shows the basic elements of an
X-ray tube. In a vacuum, inside a glass envelope,
electrons from a heated filament are accelerated by a
high voltage. The stream of high energy electrons is
focused onto a small spot on a target. Often the target is
tungsten, because of its properties of high melting point
and high density. A high proportion of the energy in the
electron beam is transferred as heat and the target has
to have an efficient means of dissipating the heat.
X-rays are produced in all directions and the tube has to
have a shield. Through a port, a beam of radiation is produced. This goes through filters to reduce the unwanted
energies and produce a useful beam for radiography.
X-rays can also be produced by a radioactive process
called Electron Capture, where the nucleus absorbs
an electron from an inner shell and X-rays are then
produced when an electron from an outer shell ‘drops
down’ to fill the space. Iron-55 is an example.
