5. X-RAY TUBE
X -rays are produced in an x-ray tube.
The x-ray tube has several parts as
follows:
- protective housing.
- Glass envelope.
- Cathode.
- Anode.
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X -rays are produced in an x-ray tube.
The x-ray tube has several parts as
follows:
- protective housing.
- Glass envelope.
- Cathode.
- Anode.
6. Protective housing;
Maintains (electronic) vacuum.
- Prevents excessive radiation exposure; allows only
useful beam out.
- Prevents electric shock, it has specifically designed
high tension receptacles.
- Limits amount of leaking radiation.
It offers mechanical support.
- It contains oil, which is electrical insulator and offers
thermal cushion.
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Maintains (electronic) vacuum.
- Prevents excessive radiation exposure; allows only
useful beam out.
- Prevents electric shock, it has specifically designed
high tension receptacles.
- Limits amount of leaking radiation.
It offers mechanical support.
- It contains oil, which is electrical insulator and offers
thermal cushion.
7. Glass envelope:
Made of pyrex glass material.
It has a ‘tube window’; which is a thin
area of 5 x 2 cm where x-rays pass.
Maintains ( electronic ) vaccum.
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Made of pyrex glass material.
It has a ‘tube window’; which is a thin
area of 5 x 2 cm where x-rays pass.
Maintains ( electronic ) vaccum.
8. Cathode
It is the negative part of x-ray tube.
It has two primary parts:
Filament and
Focusing cup
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It is the negative part of x-ray tube.
It has two primary parts:
Filament and
Focusing cup
9. Cathode; filament:
It is a coil of about 2mm thick (diameter) and
1 to 2 cm long.
Electrons are excited when heated –
thermionic emission.
Usually made of thoriated tungsten.
- Higher thermionic emission.
- Melting point is 3410 C.
- Addition of thorium increases efficiency of
thermionic emission.
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It is a coil of about 2mm thick (diameter) and
1 to 2 cm long.
Electrons are excited when heated –
thermionic emission.
Usually made of thoriated tungsten.
- Higher thermionic emission.
- Melting point is 3410 C.
- Addition of thorium increases efficiency of
thermionic emission.
10. Cathode, cont.:-
The x-ray tube current is adjusted by
controlling the filament current.
Dual-focus tube
- It has two focal spots.
- Small focal spot, for fine detail
images and,
- Large focal spot, used for procedures
producing high heat.
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The x-ray tube current is adjusted by
controlling the filament current.
Dual-focus tube
- It has two focal spots.
- Small focal spot, for fine detail
images and,
- Large focal spot, used for procedures
producing high heat.
11. Cathode; the focusing cup:
Focusing cup directs electrons to a
particular area on the anode.
The effectiveness of focusing cup is
determined by:
- It’s size and shape.
- It’s charge.
- The filament size and shape.
- The position of the filament within the
focusing cup.
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Focusing cup directs electrons to a
particular area on the anode.
The effectiveness of focusing cup is
determined by:
- It’s size and shape.
- It’s charge.
- The filament size and shape.
- The position of the filament within the
focusing cup.
12. X-ray tube; anode:
Positive side of x-ray tube.
Normally, it is made of copper.
There are two types:-
- stationary and
- Rotating ( anode)
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Positive side of x-ray tube.
Normally, it is made of copper.
There are two types:-
- stationary and
- Rotating ( anode)
13. Anode; functions:
It conducts electricity.
It conducts heat.
Mechanical support for the targettarget,
which the electrons strike to produce
x-rays.
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It conducts electricity.
It conducts heat.
Mechanical support for the targettarget,
which the electrons strike to produce
x-rays.
14. Anode, the Target
The target is embedded in anode copper
block, it is made up of tungsten alloy
(rhenium).
Three main properties of tungsten:
- High atomic number:- Increased
efficiency in x-ray production and increased
high energy x-rays.
- Good thermal conductivity; it dissipates
heat quickly and a high melting point.
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The target is embedded in anode copper
block, it is made up of tungsten alloy
(rhenium).
Three main properties of tungsten:
- High atomic number:- Increased
efficiency in x-ray production and increased
high energy x-rays.
- Good thermal conductivity; it dissipates
heat quickly and a high melting point.
15. Rotating anode:
Interaction takes place on a larger
target area; there is several hundred
times more area for electron beam to
interact, than in stationary – anode
tube.
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Interaction takes place on a larger
target area; there is several hundred
times more area for electron beam to
interact, than in stationary – anode
tube.
17. ELECTRON – TARGET
INTERACTION:
Primary function of the tube is to accelerate
electrons from cathode to anode.
Large number of electrons are focused to a
small spot; they have acquired high kinetic
energy.
Kinetic energy is energy of motion.
Objects in motion have K.E. proportional to
their mass and to square of their velocity.
K.E. = ½ mv22
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Primary function of the tube is to accelerate
electrons from cathode to anode.
Large number of electrons are focused to a
small spot; they have acquired high kinetic
energy.
Kinetic energy is energy of motion.
Objects in motion have K.E. proportional to
their mass and to square of their velocity.
K.E. = ½ mv22
18. Electron – Target interaction
cont..
By increasing K.E., the intensity ( quantity
of x-rays) and energy (ability to penetrate) of
the created x-rays are increased.
The distance between filament and target,
varies from about 1 to 3 cms.
The electrons traveling from cathode to
anode comprise the x-ray tube current.
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By increasing K.E., the intensity ( quantity
of x-rays) and energy (ability to penetrate) of
the created x-rays are increased.
The distance between filament and target,
varies from about 1 to 3 cms.
The electrons traveling from cathode to
anode comprise the x-ray tube current.
19. ELECTRON – TARGET
INTERACTION cont..
Projectile electrons interact with either
orbital electrons, or nuclei of target
atoms.
Interactions result in the conversion of
K.E. into thermal energy and
electromagnetic energy in from of x-
rays.
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Projectile electrons interact with either
orbital electrons, or nuclei of target
atoms.
Interactions result in the conversion of
K.E. into thermal energy and
electromagnetic energy in from of x-
rays.
20. ANODE HEAT:
The outer –shell electrons are simply raised
to an excited, or higher energy level.
When they drop back to their normal energy
level or state they emit infrared radiations.
Constant excitation and destabilization of
outer- shell electrons is responsible for the
heat generated in x-ray tubes.
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The outer –shell electrons are simply raised
to an excited, or higher energy level.
When they drop back to their normal energy
level or state they emit infrared radiations.
Constant excitation and destabilization of
outer- shell electrons is responsible for the
heat generated in x-ray tubes.
21. Generation of x-rays
More that 99% of K.E. of projectile
electrons is converted to thermal
energy, only about 1% is available for
x-radiation production.
The efficiency of x-ray production is
independent of the tube current;
efficiency increases with increasing
projectile electrons energy.
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More that 99% of K.E. of projectile
electrons is converted to thermal
energy, only about 1% is available for
x-radiation production.
The efficiency of x-ray production is
independent of the tube current;
efficiency increases with increasing
projectile electrons energy.
22. Characteristic Radiation:-
When projectile electrons interacts
with an inner shell electrons of target
atom ( rather than outer shell electron )
characteristic x – radiation is
produced.
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When projectile electrons interacts
with an inner shell electrons of target
atom ( rather than outer shell electron )
characteristic x – radiation is
produced.
23. Characteristic Radiation:-
Characteristic x-radiations result when
the interaction is sufficiently violent to
ionize the target atom by removal of an
inner shell electron. Excitation of an
inner shell electron only does not
produce characteristic x- radiation.
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Characteristic x-radiations result when
the interaction is sufficiently violent to
ionize the target atom by removal of an
inner shell electron. Excitation of an
inner shell electron only does not
produce characteristic x- radiation.
24. Characteristic Radiation, cont..
Characteristic radiations are produced by
transitions of orbital electrons from outer to
inner shells, depending on electron binding
energy of that element.
This type of x – radiation is called
characteristic radiation because it is
characteristic of target element.
The effective energy of characteristic x- rays
increases with the atomic no. of the target
element.
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Characteristic radiations are produced by
transitions of orbital electrons from outer to
inner shells, depending on electron binding
energy of that element.
This type of x – radiation is called
characteristic radiation because it is
characteristic of target element.
The effective energy of characteristic x- rays
increases with the atomic no. of the target
element.
26. Bremsstrahlung radiation:-
Projectile electrons can loose they K.E.,
when they interact with the nucleus of target
atom; the energy lost re appears as
electromagnetic energy.
As it passes by the nucleus, it is slowed and
deviated in it’s course, as a result leaving
with reduced K.E. going in a different
direction. This loss in K.E. re-appears as x-
ray photons.
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Projectile electrons can loose they K.E.,
when they interact with the nucleus of target
atom; the energy lost re appears as
electromagnetic energy.
As it passes by the nucleus, it is slowed and
deviated in it’s course, as a result leaving
with reduced K.E. going in a different
direction. This loss in K.E. re-appears as x-
ray photons.
27. Bremsstrahlung radiation
cont…
A low energy bremsstrahlung x-ray
results when the projectile electron is
barely influenced by the nucleus.
A maximum energy x-ray occurs when
the projectile electrons lose all their
K.E and simply drifts away from the
nucleus.
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A low energy bremsstrahlung x-ray
results when the projectile electron is
barely influenced by the nucleus.
A maximum energy x-ray occurs when
the projectile electrons lose all their
K.E and simply drifts away from the
nucleus.
28. Bremsstrahlung radiation,
cont.:-
Bremsstrahlung radiation can be
considered as radiation resulting from
braking of projectile electrons by the
nucleus. Most x-rays are of
bremsstrahlung in origin.
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Bremsstrahlung radiation can be
considered as radiation resulting from
braking of projectile electrons by the
nucleus. Most x-rays are of
bremsstrahlung in origin.
