This document provides information about x-rays and the components responsible for their production. It discusses the history of x-ray discovery by Wilhelm Röntgen in 1895. It then describes the key components of an x-ray tube, including the cathode which emits electrons, and the anode which converts the electron energy into x-rays. The document explains how tungsten is commonly used for the filament and target due to its high melting point and ability to efficiently produce x-rays. It also discusses factors like focal spot size and line focus principle which allow controlling the size and shape of the x-ray beam.

1. PRODUCTION AND
PROPERTIES OF X-RAY
PRESENTER:Sr.Rt.Manoj Kumar Mandal

2. HISTORY OF X-RAY
X-rays are a penetrating form of high energy electromagnetic radiation that are located between the UV and
gamma rays in the electromagnetic spectrum. They were first discovered on 8 November 1895 when
Wilhelm Conrad Röntgen stumbled across their effects to create images on fluorescent screens, and
subsequently on photographic plates, at a distance from an optically hidden Crookes, or similar, tube. This would
mean that X-rays would have been produced by experimenters from as early as 1875, when Crookes tubes, and
their like, were first created.
However, it was Röntgen that first saw their effect and which he described in his paper “On A New Kind of
Rays” that was published on 28 December 1895. Röntgen called his discovery X-rays to indicate that it was,
then, an unknown type of radiation. However, in many languages to this day they are still known as Röntgen
rays.
This discovery was recognised in 1901 when Röntgen was awarded the first Nobel prize for Physics. Since
the discovery of X-rays, their use for analysis and diagnostics have been some of the most widely researched
areas in science and engineering. It is amazing to note that in the first quarter of the 20th century, almost half of
the Nobel prizes awarded were connected to contributions in this area.Röntgen was quick to see the medical
implications and opportunities of his discovery, as the famous first X-ray image of his wife Anna’s hand on 22
December 1895 shows. He realised that X-rays provided a non-invasive method to investigate inside the body. It
is interesting to note that, for personal ethical reasons, Röntgen refused to take out patents on his discovery of
X-rays, as he wanted society, as a whole, to benefit from their practical applications.

3. TYPES OF RADIATION
Electromagnetic radiation (EMR) consists of waves. The waves contain electric and magnetic energy.
The electromagnetic spectrum (EMS) includes different types of energy waves. At one end of the
spectrum, there are very low energy waves. Radio waves are an example of low energy waves. At the
other end of the spectrum, there are very high energy waves. Gamma rays are an example of high energy
waves.
Particle radiation is made up of atomic or subatomic particles. These particles include protons, neutrons
and electrons. They all have kinetic energy. That’s the energy is the energy an object has when it’s in
motion.

4. CONT.
EMR

5. CONT.

6. CONT.

7. COMPONENT RESPONSIBLE FOR X-RAY
PRODUCTION
ANODE SIDE Genreator components CATHODE SIDE
Target Material The tube Filament
Anode High voltage generator Focusing cupmolybidium(mo)
Heel Effect:Applicationfactor Control console Filament current
Target, focus, focal point, focal
spot:
Colling system Dual focus
Actual focal spot Effective modern xray has 2 filament
Effective focal spot
Line focus
Mosely’s law
Auger effect

8. HIGH VOLTAGE GENERATOR
X-ray units require a high voltage generator to achieve the necessary power required of an x-ray tube. AC
power will supply x-ray units with (AC)sinusoidal currents, resulting in 'peaks and troughs', limiting an x-
ray tube to produce x-rays only half of the 1/60th of s second cycle.
Modern x-ray units, which largely utilize, constant potential generators do not have
'voltage ripple' and consequently employ the term kV rather than kVp.
PICTURE SHOWING COMMERCIAL MODEL OF HIGH VOLTAGE GENERATOR
USED IN XRAY

9. X-RAY TUBE
• X-ray tube, also called Roentgen tube, evacuated electron tube that produces X rays by accelerating
electrons to a high velocity with a high-voltage field and causing them to collide with a target, the anode
plate. The tube consists of a source of electrons, the cathode, which is usually a heated filament, and a
thermally rugged anode, usually of tungsten, which is enclosed in an evacuated glass envelope. The
voltage applied to accelerate the electrons is in the range of 30 to 100 kilovolts. The X-ray tube
functions on the principle that X rays are produced wherever electrons moving at very high speeds
strike matter of any kind. Only about 1 percent of the electron energy is converted to X rays. Because X
rays can penetrate solid substances to varying degrees, they are applied in medicine and dentistry, in
the exploration of the structure of crystalline materials, and in research.

10. CONT.:TECHNICAL AND COMMERCIAL
MODEL

11. ANODE
The anode (or anticathode) is the component of the x-ray tube where x-rays are produced. It is a
piece of metal, shaped in the form of a bevelled disk with a diameter between 55 and 100 mm, and
thickness of 7 mm, connected to the positive side of the electrical circuit. The anode converts the
energy of incident electrons into x-rays dissipating heat as a byproduct.

12. ANODE
Target, focus, focal point, focal spot: where electrons hit the anode
Actual focal spot: physical area of the focal track that is impacted
Focal track: portion of the anode the electrons bombard. On a rotating anode this is a circular path
Effective focal spot: the area of the focal spTarget, focus, focal point, focal spot: where electrons hit the
anode
Heating of the anode
This is the major limitation of x-ray production.
Heat (J) = w x kVp x mAs
key:
kVe = effective kV
w = waveform of the voltage through the x-ray tube. The more uniform the waveform the lower the heat production
kVp = peak kV
mAs = current exposure time product
Heat is normally removed from the anode by radiation through the vacuum and into the conducting oil outside the glass envelope. The molybdenum
stem conducts very little heat to prevent damage to the metal bearings.
Heat capacity
A higher heat capacity means the temperature of the material rises only a small amount with a large increase in heat input.
Temperature rise = energy applied / heat capacity

13. CONT.
Structure:
Most x-ray tube anodes are made of tungsten (the target material). Tungsten has a high atomic number (Z=74)
and a high melting point of 3370°C with a correspondingly low rate of evaporation. The high atomic number of
tungsten gives more efficient bremsstrahlung production compared to lower atomic number target materials. An
alloy containing tungsten and rhenium is also used because the addition of 5-10% rhenium prevents grazing of the
anode surface. The body of the anode is made of materials that are light and have a good heat storage capacity,
like molybdenum and graphite. Molybdenum is also often used as the target material for anodes used in
mammography because it has an intermediate atomic number (Z=42) and the produced characteristic x-rays are of
energies suited for this purpose. Some anodes used in mammography are also made of rhodium (Z=45), which
has characteristic x-rays of slightly higher energies, which are more penetrating and preferably used in dense
breast imaging.
TYPES:
-STATIONARY
-ROTATING -
STATIONARY ANODE:For X-ray examinations that require infrequent exposures or low anode current such as in
dental units, portable X ray units and portable fluoroscopy systems, only stationary anode is required
-ROTATING ANODE:Anodes are designed as bevelled disks attached to a large copper rotor of the electric
motor, rotating them at the speeds up to 10,000 rpm, with a temperature of 2000°C. The purpose of the rotation is to
dissipate heat. Most rotating anodes actually represent rather complex electromechanical systems consisting of
approximately 350 pieces, taking around 150 assembly operations.

14. FOCAL SPOT
The anode disc rotates and is subjected to a focused beam of electrons emanating from the cathode, which is
accelerated by a high potential difference between the cathode and the anode. When the electron beam hits the anode
(at the actual focal spot), interactions of the electrons with the target material produces the x-ray beam. The anode
angle is the angle between the vertical and the target surface with most x-ray tubes having an anode angle of 12-15°. A
smaller angle results in a smaller effective focal spot.
The whole anode is not included in x-ray production. X-rays are produced on the rather small rectangular surface, the
actual focal spot.The focal spot is the area of the target upon which the electron beam impinges. The energy of the
electrons in the electron beam is mostly converted into heat (approximately 99%, which is why materials such as
tungsten are used due to their high melting-points) and dissipated uniformly across the focal spot and anode surface.
The x-rays produced at the anode comprise less than one percent of the energy of the electrons in the electron beam.
A large focal spot is therefore useful to protect the tungsten target as the heat accumulates and dissipates within the
area of focal spot. However, a small focal spot is required to achieve good radiographic image quality.
Thus the line focus principle helps resolve this issue by stating that angulation of the anode surface will result in an
apparent decrease in the focal spot size.
The apparent focal spot (projected focal spot) size can be determined by the sine of the angle of the anode surface
(apparent focal spot size = real focal spot size * sin anode angle). The angle varies as per tube design with a range
value of 6 degrees to about 20 degrees.

15. A and B, As the filament size decreases, both actual and effective focal spots decrease in size. The line-focus
principle results in an effective focal spot that is smaller than the actual focal spot. C and D, As the anode angle
decreases, both actual and effective focal spots decrease in size.

16. FOCAL SPOT

17. LINE FOCUS PRINCIPLE
The line focus principle in radiography explains the relationship between the actual
focal spot on the anode surface and the effective focal spot size.
Limitation of the principle
There are two important aspects to consider with regards to target angle:
size of the apparent focal spot
area covered by the x-ray beam
Firstly, for a given apparent focal spot size, the real area covered by the electron beam
is larger for smaller target angles which, as stated above allows a greater area over
which to dissipate the heat.
Secondly, for a smaller target angle, the area covered by the x-ray beam will be smaller
so it is not possible to cover large areas at smaller focus film distances (FFDs),
therefore it can be appreciated that choice of target angle is a compromise between
tube loading, geometric unsharpness, and desired area to be covered by the useful
beam. For practical purpose, at 40" FFD the anode angle should be no smaller than 15
degrees. A decrease in angle below six degrees will result in anode heel effect.

18. Exposure field coverage increases as anode
angle increases.

19. ANODE HEEL EFFECT
Anode heel effect refers to the lower field intensity towards the anode in comparison to the cathode due to
lower x-ray emissions from the target material at angles perpendicular to the electron beam.The
conversion of the electron beam into x-rays doesn’t simply occur at the surface of the target material but
deep within it. Because x-rays are produced deep in the target material they must traverse back out of it
before they can proceed to the target field. More target material needs to be traversed at emission angles
that are perpendicular to the electron beam (closer to the anode) than at those more parallel to it (closer to
the cathode). This increase in material leads to more resorption of the x-rays by the target material
resulting in fewer x-rays reaching the field at angles perpendicular to the electron beam. It also means that
the x-rays emitted to angles closer to the incident beam travel through less target material and fewer are
resorbed.

20. FACTOR AND APPLICATION OF ANODE
HEEL EFFECT:
Factors:
Anode angle: by increasing the angle, the amount of target material perpendicular to the anode is decreased resulting in
less resorption of x-rays produced.
Target-to-film distance: increase in distance reduces heel effect by allowing more divergence of the beam which
produces a more uniform image.
Field size: the field will be more uniform at the center (i.e. smaller field size) due to the collimator absorbing the
peripheral variations.
Positioning: by aligning higher attenuating material towards the cathode and lower attenuating material towards the
anode the resulting field is more uniform
Applications:
Anode heel effect can benefit in X-ray imaging by aligning the anode-cathode axis parallel to thinner-thicker sections of
the patient's body, thus equalising the patient's exposure to X-rays and produce a more uniform image. Anode heel
effect have shown positive results in the imaging of kidneys, ureter, and bladder (KUB), skull, chest, pelvis, abdomen,
thoracic, lumbar, and extremities .
Mammography also utilizes anode heel effect to its advantage by aligning the cathode close to the thoracic wall (thicker
and denser) and anode close to the nipple (thinner) .

21. ANODE HEEL EFFECT

22. CATHODE
The cathode is part of an x-ray tube and serves to expel the electrons from the circuit and focus them
in a beam on the focal spot of the anode. It is a controlled source of electrons for the generation of x-
ray beams. The electrons are produced by heating the filament (Joule heating effect) i.e. a coil of wire
made from tungsten, placed within a cup-shaped structure, a highly polished nickel focusing cup,
providing electrostatic focusing of the beam on the anode.
In order to expel the electrons from the system, they need to be given the energy. Heat is used to
expel the electrons from the cathode. The filament is crystallized during construction and its
crystallized structure gives the filament stability. The process is called thermionic emission (or Edison
effect). The filament is heated with the electric current passing through it (to the glowing temperature)
and the electrons are then expelled from the cathode.

23. CATHODE
Filament
The filament is a coil of wire similar to that in a kitchen toaster except much smaller. The filament is usually
approximately 2 mm in diameter and 1 to 2 cm long. In a kitchen toaster, an electric current is conducted through
the coil, causing it to glow and emit a large quantity of heat. An x-ray tube filament emits electrons when it is
heated. When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms
are “boiled off” and ejected from the filament. This phenomenon is known as thermionic emission. Filaments are
usually made of thoriated tungsten. Because tungsten provides for higher thermionic emission than other metals.
Its melting point is 3410° C, and therefore it is not likely to burn out like the filament of a light bulb.
Focusing Cup
The filament is embedded in a metal cup called the focusing cup. Because all the electrons accelerated from
cathode to anode are electrically negative, the electron beam tends to spread out owing to electrostatic repulsion.
Some electri=ons can even miss the anode completely. The focusing cup is negatively charged so that it
electrostatically confines the electron beam to a small area of the anode.
Effectiveness of Focusing Cup is determined by:
-Size
- Shape
- Charge
- Filament size and shape
- Position of the Filament in the focusing cup

24. CONT.
Filament Current
When the x-ray imaging system is first turned on, a low current passes
through the filament to warm it and prepare it for the thermal jolt necessary for x-ray production. At
low filament current, there is no tube current because the filament does not get hot enough for
thermionic emission. Once the filament current is high enough for thermionic emission, a small rise
in filament current results in a large rise in tube current.
Dual Focus
Most diagnostic x-ray tube have two focal spot, one large and the other is small. The
small focal spot is used when better spatial resolution is required. The large focal spot is
used when large body parts are imaged and when other techniques that produced high heat
are required. Normally, either filament can be used with the lower mA station, approximately
300 mA or less. At approximately 400 mA and up, only the larger focal spot is allowed
because the heat capacity of anode could be exceeded if the small focal spot were used.
The size of small focal spot ranges from 0.1 to 1 mm; large focal spots usually ranges from
0.3 to 2 mm. The small focal size is associated with the small filament and the large focal
spot size with the large filament.

25. TARGET AND FILAMENT=TUNGSTEN
WHY?
Tungsten (chemical symbol, W) is a hard refractory metallic element with remarkable
resilience which forms the basis for its industrial uses. It is the metal of choice in the filaments
and targets of x-ray tubes. There is no evidence that tungsten is required by the human body,
although some micro-organisms do use it.ungsten has the atomic number 74 and a relative
atomic weight of 183.84 1. It is located in group VIb of the periodic table beneath chromium and
molybdenum. It has the highest melting point of any metal at 3422°C, the lowest vapor pressure
(low tendency to evaporate) and the highest tensile strength at high temperatures (>1650°C). Its
density is 19.3 g/cm3, only very slightly less than gold (19.32 g/cm3) 1,4. Tungsten has high
resistance to electricity and thus is able to produce large amounts of heat when an electrical
current passes through it. Tungsten resistivity also increases with an increase in temperature .

26. BASIC INFORMATION
Basic Information
• Name: Tungsten
• Symbol: W
• Atomic Number: 74
• Atomic Mass: 183.84 amu
• Melting Point: 3410.0 °C (3683.15 K, 6170.0 °F)
• Boiling Point: 5660.0 °C (5933.15 K, 10220.0 °F)
• Number of Protons/Electrons: 74
• Number of Neutrons: 110
• Classification: Transition Metal
• Crystal Structure: Cubic
• Density @ 293 K: 19.3 g/cm3 JUST AS GOLD
• Color: Silver`
NOTE:From the diagram above, that the binding energy of the K-shell electrons in tungsten atoms is
69.5 keV. What this means is that if we want to remove one of those electrons from the atom, we would need
to give it an energy is excess of 69.5 keV. To remove an L-shell electron, a lower energy of just 10.2 keV would
be required.

27. OVER VIEW :PRODUCTION OF X-RAY
1.A current is passed through the tungsten filament and heats it up.
2.As it is heated up the increased energy enables electrons to be released from the filament through thermionic
emission.
3.The electrons are attracted towards the positively charged anode and hit the tungsten target with a maximum energy
determined by the tube potential (voltage).
4.As the electrons bombard the target they interact via Bremsstrahlung and characteristic interactions which result in
the conversion of energy into heat (99%) and x-ray photons (1%).
5.The x-ray photons are released in a beam with a range of energies (x-ray spectrum) out of the window of the tube and
form the basis for x-ray image formation.

28. CONT.
Window: made of beryllium with aluminium or copper to filter out the soft x-rays. Softer (lower energy) x-
ray photons contribute to patient dose but not to the image production as they do not have enough energy
to pass through the patient to the detector. To reduce this redundant radiation dose to the patient these x-
ray photons are removed.
Glass envelope: contains vacuum so that electrons do not collide with anything other than target.
Insulating oil: carries heat produced by the anode away via conduction.
Filter: Total filtration must be >2.5 mm aluminium equivalent (meaning that the material provides the same
amount of filtration as a >2.5 mm thickness of aluminium) for a >110 kV generator
Total filtration = inherent filtration + additional filtration (removable filter)

29. PRODUCTION OF X-RAY
1. Electrons produced: thermionic emission
A current is applied through the cathode filament, which heats up and releases electrons via thermionic emission. The
electrons are accelerated towards the positive anode by a tube voltage applied across the tube. At the anode, 99% of
energy from the electrons is converted into heat and only 1% is converted into x-ray photons. The accelerating
potential is the voltage applied across the tube to create the negative to positive gradient across the tube and
accelerate the electrons across the anode. It is normally 50-150 kV for radiography, 25-40 kV for mammography and
40-110 kV for fluoroscopy. UK mains supply is 230 V and 50 Hz of alternating current. When the charge is negative the
accelerating potential is reversed (the cathode becomes positive and the anode becomes negative). This means that
the electrons are not accelerated towards the anode to produce an x-ray beam. The ideal waveform for imaging is a
positive constant square wave so that the electron flow is continuously towards the anode. We can convert the standard
sinusoidal wave into a square wave by rectification.

30. Producing an x-ray beam

31. Producing an x-ray beam
Full wave rectification: the use of a rectification circuit to convert negative into positive voltage. However, there are still
points at which the voltage is zero and most of the time it is less than the maximum kV (kVp). This would lead to a lot of
lower energy photons. There are two rectification mechanisms that prevent too many lower energy photons:
Three phase supply: three electrical supplies are used, each applied at a different time. The “ripple” (difference
between maximum and minimum current) is about 15% of the kVp.
High frequency generator: this can supply an almost constant potential. The supply is switched on and off rapidly
(14kHz) which can then be rectified. They are much more compact than three phase supply and more commonly used.
Effect of rectification on spectrum:
Increased mean photon energy – fewer photons of lower energy
Increased x-ray output – stays closer to the maximum for longer
Shorter exposure – as output higher, can run exposure for shorter time to get same output
Lower patient dose – increased mean energy means fewer low energy photons that contribute to patient dose but do
not contribute to the final image

32. CURRENT
Filament current:
The current (usually 10 A) heats up the filament to impart enough energy to the electrons to be released
i.e. it affects the number of electrons released.
Tube current:
This is the flow of electrons to the anode and is usually 0.5 – 1000 mA.
Summary:
Filament current is applied across the tungsten cathode filament (10 A) and affects the number of
electrons released.
Tube current is applied across the x-ray tube from cathode to anode and affects the energy and number of
electrons released.

33. X-RAY PRODUCTION AT THE ANODE
The electrons hit the anode with a maximum kinetic energy of the kVp and interact with the anode by
losing energy via:
Elastic interaction: rare, only happens if kVp < 10 eV. Electrons interact but conserve all their energy
Ineleastic interaction: causes excitation / ionisation in atoms and releases energy via electromagnetic (EM)
radiation and thermal energy
Interactions:
At the anode, electrons can interact with the atoms of the anode in several ways to produce x-ray photons.
Outer shell interaction: low energy EM released and quickly converted into heat energy
Inner shell interaction: produces characteristic radiation
Nucleus field interaction: aka Bremsstahlung

34. Characteristic radiation
Characteristic radiation:
A bombarding electron knocks a k-shell or l-shell electron out.
A higher shell electron moves into the empty space.
This movement to a lower energy state releases energy in the form of an x-ray photon.
The bombarding electron continues on its path but is diverted.

35. CONT.
It is called “characteristic” as energy of emitted electrons is dependent upon the anode material, not on the
tube voltage. Energy is released in characteristic values corresponding to the binding energies of different
shells.
For tungsten:
Ek – El (aka Kα) = 59.3 keV
Ek – Em (aka Kβ) = 67.6 keV

36. Bremsstrahlung
1-Bombarding electron approaches the nucleus.
2-Electron is diverted by the electric field of the nucleus.
3-The energy loss from this diversion is released as a photon (Bremsstrahlung radiation).
Bremsstrahlung causes a spectrum of photon energies to be released. 80% of x-rays are emitted via
Bremsstrahlung. Rarely, the electron is stopped completely and gives up all its energy as a photon. More
commonly, a series of interactions happen in which the electron loses energy through several steps.

37. VS....
Characteristic radiation Bremsstrahlung
1.Only accounts for small percentage of x-ray
photons produced
1.Accounts for 80% of photons in x-ray beam
2.Bombarding electron interacts with inner shell
electron
2.Bombarding electron interacts with whole atom
3.Radiation released due to electron dropping down
into lower energy state
3.Radiation released due to diversion of bombarding
electron as a result of the atomic pull
4.adiation released is of a specific energy 4.Radiation released is of a large range of energies
5.X-ray photon energy depends on element of target
atoms not tube voltage
5.X-ray photon energy depends on tube voltage

38. PROPERTIES OF X-RAY
X-rays are a type of electromagnetic radiation, and have several unique properties that make them useful in a wide variety of
applications. Some of the properties of X-rays include:
1.High energy: X-rays have much higher energy than visible light, ultraviolet light, and infrared light. This high energy allows them to
penetrate through many materials, including soft tissue and bone.
2.Wavelength: X-rays have a shorter wavelength than visible light and other forms of electromagnetic radiation. This property allows
them to produce highly detailed images of the inside of the body, as well as other materials.
3.Ionizing radiation: X-rays have enough energy to knock electrons out of atoms, a process called ionization. This can cause damage to
living cells, which can lead to cancer if exposure is high and prolonged.
4.No charge: X-rays are neutral, they don’t carry any charge, this can make them penetrate through materials that are not affected by
charged particles.
5.Reflection and refraction: X-rays can be reflected and refracted by different materials, similar to visible light. This allows them to be
focused and directed for imaging and other applications.
6.Interaction with matter: X-rays interact with matter differently than visible light, they can penetrate through some materials, be
absorbed, scattered or reflected.
7.Interaction with biological systems: X-rays can penetrate through soft tissue, but are absorbed by denser materials such as bone.
This allows them to produce images of the inside of the body, and to be used in medical and dental applications.
It’s important to note that X-rays are ionizing radiation, which means they can damage living cells, and prolonged exposure can
lead to cancer. Safety precautions are taken in the handling and use of X-ray equipment to minimize any risks.

39. THANK YOU