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2. X-rays are
produced due to sudden deceleration of fast-moving electrons when
they
collide and interact with the target anode. In this process of deceleration, more
than
99% of the electron energy is converted into heat and less than 1% of energy
is
converted into x-rays.
Cathode
The
cathode is the negative terminal of an x-ray tube. It is a tungsten filament and
when
current flows through it, the filament is heated and emits its surface electrons
by
a process called thermionic emission.
Kilovoltage
High
voltage, in the kilovolt range (1000 volts), is applied between the cathode and
anode.
This causes electrons to move towards the positive terminal (anode) of the
tube
at a velocity of half the speed of light (c).
Anode
The
positive terminal of the tube. It is made of a tungsten disc in ordinary
diagnostic
x-ray tubes. Fast-moving electrons interact with the anode in the
following
ways: 
interaction
with K-shell electron: causes the production of characteristic radiation
interaction
with nucleus: causes bremsstrahlung radiation
interaction
with outer shell electrons: causes line spectrum
X-ray tube

4. X-ray production
To summarize, x-rays are produced in a standard way: by heating a filament, which releases
electrons by
 
thermionic emission, accelerating electrons with a high voltage and allowing
them to collide with the
 
focal spot 
on the target/anode. X-rays are produced via two
interactions in the anode.
Bremsstrahlung x-rays
Bremsstrahlung x-rays (German for "braking") - electrons lose kinetic energy as they pass
through atoms in the anode because they are attracted to the positively charges nuclei. The
closer to the nucleus the electron passes, the more kinetic energy it loses and it is deflected
to continue moving in another direction at lower energy, or stopped altogether. This is
where maximum kinetic energy is transferred to the production of an x-ray that is emitted
from the anode.
Characteristic x-rays
If electrons possess an energy that is equivalent to, or greater than, the binding energy of the
orbiting electrons in target atoms, these electrons are likely to be ejected from the atom.
This most often occurs in the inner electron shell (K-shell). The ejected electron is known as
a photoelectron. The vacancy left in the K-shell must be filled in order for the atom to
remain stable (law of conservation of energy) so outer shell electrons drop down to fill the
shell. This process of electron transfer between shells produces x-rays that are
"characteristic" of the binding energies of that particular atom/material, hence the name.

6. •Bremsstrahlung
Bremsstrahlung is the radiative energy loss of
moving charged particles as they interact with the
matter. The attractive force slows down the
electron, deflecting it from its original path. The
kinetic energy that the particle loses is emitted as a
photon. Bremsstrahlung production is enhanced for
high Z materials and high energy electrons.

9. X-rays are a form of
 electromagnetic radiation with wavelengths ranging from 0.01 to 10
nanometers. In the setting of diagnostic radiology, X-rays have long enjoyed use in the imaging
of body tissues and aid in the diagnosis of disease. Simply understood, the generation of X-rays
occurs when electrons are accelerated under a potential difference and turned into
electromagnetic radiation.
 An X-ray tube, with its respective components placed in a vacuum,
and a generator, make up the basic components of X-ray production. Essential components of an
X-ray tube include a cathode, and an anode separated a short distance from each other, a vacuum
enclosure, and high voltage cables forming the X-ray generator attached to the cathode and
anode components. In the generation of X-ray production, a cathode filament machined in a
cathode cup is activated, causing intense heating of the cathode filament.
 The heating of the
filament leads to the release of electrons in a process called thermionic emission.
 The released
electrons form in an electron cloud at the filament surface, and repulsion forces prevent the
ejection of electrons from this negatively charged cloud.
 Upon application of a high voltage by
an X-ray generator to the cathode as well as the anode, there is an acceleration of electrons
ejected to an electrically positive anode.
 The filament and the focusing cup determine this path of
acceleration.
 

10. Once
the high kinetic energy electrons finally reach the anode target, this initiates the
process
of X-ray production. Tungsten is often the usual anode target, although other
material
targets are also employed. Electrons come extremely close to the nucleus of
the
target, causing a deceleration and change in direction, converting the kinetic energy
to
electromagnetic radiation in a process known as “
braking
radiation
”
or
bremsstrahlung. The
output is a spectrum of X-ray energies. Incident electrons can also
result
in ionization, whereby the approaching electron can remove a second electron
belonging
to an atom of the anode target, losing its energy through ionization or
excitation.
This process leads to an emission of a photon as the electron orbit vacancy
gets
filled by an orbital shell electron from a further out shell. Considering orbital
energies
and their differences are unique in atoms, this leads to a “
characteristic
X-ray
”

with
energies that can serve as a fingerprint unique to each anode target.
Bremsstrahlung X-rays, however, constitute the majority of X-rays produced in
this process.
 

11. X radiation and matter interact mainly by three different
mechanisms, Compton scattering, pair production and
the photoelectric effect. The different contributions of
these to absorption depend on the absorbing material,
principally its atomic number Z and the quantum
energy E of the incident photon,

12. X-Ray ABSORPTION The Photoelectric Effect
During
X-ray imaging, the photoelectric effect largely predominates. Photon absorbed and disappeared 
•gamma ray of low energy, or one that has lost most of its energy through Compton interactions, may transfer its remaining energy to an orbital (generally
inner-shell) electron. High Z materials

14. b. Compton Scattering
In
Compton scattering the incident photon
transfers
part of its energy to an outer shell or
(essentially)
“free” electron, ejecting it from the
atom.
Upon ejection this electron is called a
Compton electron.
The photon is scattered at an
angle
that depends on the amount of energy
transferred
from the photon to the electron.
During radiotherapy treatment, the Compton
effect largely predominates.
High
energy photon- low Z materials-outer shell
electrons

15. b. Compton Scattering

16. c. Pair Production
•A
third type of interaction of photons with matter,
pair production,
only
occurs
with very high photon energies (greater than 1.02 MeV)

17. By that effect the gamma-ray is transformed to matter in the form of a pair of negatively and positively charged electrons
(negatron and positron). Because an electron has a rest mass equivalent to 0.511 MeV of energy, a minimum gamma-
energy of 1.02 MeV is required for this pair production. Any excess energy of the pair-producing gamma-ray is given to
the electron–positron pair as kinetic energy. Most probably the positron will undergo annihilation by reaction with an
electron in the detector material and by that two gamma photons of 0.511 MeV each will be created.

18. Before understanding the final production of an X-ray image, it is essential to
understand the interaction of X-rays with individuals exposed to X-rays. There
are three important types of interactions that occur between X-rays and the
tissues of our body. In “Compton” scattering, X-rays of higher energy strike an
outer shell electron and are strong enough to remove it from the shell, causing
ionization of an atom.
 This phenomenon contributes to dose and also
contributes to scatter. Photoelectric interactions occur when an incoming X-ray
strikes an inner shell electron, removing it from the shell and causing a
downward cascade of outer shell electrons filling inner orbit vacancies, further
releasing secondary X-rays. This type of
 interaction contributes to image
contrast. Pair production (PP),
like the photoelectric effect, results in
the
complete attenuation of the incident photon. Pair production can
only
occur if the incident photon energy is at least 1.022 MeV. As the
photon
interacts with the strong electric field around the nucleus it
undergoes
a change of state and is transformed into two particles
(essentially
creating matter from energy):
one
electron
one
positron

19. •Finally, the differential absorption of X-rays within the
tissues of the body subsequently contributes to the
production of the final image. Attenuation of X-rays
ultimately depends on the effective atomic number in
tissue, X-ray beam energy, and tissue density.

21. •Methods of Radioactive Decay

22. FILM STRUCTURE
Conventional film is layered, as illustrated in the following figure. The active
component is an emulsion layer coated onto a base material. Most film used in
radiography has an emulsion layer on each side of the base so that it can be used
with two intensifying screens simultaneously. Films used in cameras and in
selected radiographic procedures, such as mammography, have one emulsion
layer and are called single-emulsion films.

23.  Base
The
base of a typical radiographic film is made of a clear polyester material about
150
µm thick. It provides the physical support for the other film components and
does
not participate in the image-forming process.
Emulsion
The
emulsion is the active component in which the image is formed and consists
of
many small silver bromide crystals suspended in gelatin. The gelatin supports,
separates,
and protects the crystals. 
X-ray film displays
the radiographic image and consists of emulsion of silver
bromide
(AgBr) which when exposed to radiation, produces black metallic silver
are
formed.