Production of x rays

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Production of X Rays:

Production of X Rays Dr. Varun Babu MD Resident Dept. of Radiology AIMS, Cochin 1 June 2011

X ray tube:

X ray tube

X ray tube:

X ray tube

Diagnostic X ray tubes:

Diagnostic X ray tubes Made of Pyrex glass that encloses a vacuum containing two electrodes. Cathode electrons Anode Why Vacuum?



X ray tube Current:

X ray tube Current Number of electrons flowing per second from filament to target mA


Filament Tungsten wire Thermionic emission Thermal energy Electron emission Tungsten thermions (2000 0 C)

Space charge and Space charge effect:

Space charge and Space charge effect Space Charge Electrons emitted from the tungsten filament form a small cloud in the immediate vicinity of the filament. Prevents other electrons from being emitted from the filament until they have acquired sufficient thermal energy to overcome the force caused by the space charge Space charge effect Tendency of the space charge to limit the emission of more electrons from the filament

Cathode Focusing Cup:

Cathode Focusing Cup Prevents the forces of mutual repulsion of electrons resulting in spreading out and bombardment of anode over a large area Nickel

Line Focus Principle:

Line Focus Principle Of the electrons striking the anode, <1% is converted to X rays, remaining is heat

Anode - Types:

Anode - Types

Stationary Anode:

Stationary Anode Small plate of tungsten embedded in a large mass of Copper

Rotating Anode:

Rotating Anode A large disc of tungsten/alloys of tungsten, which theoretically rotates at speed of about 3600 rpm

Rotating Anode:

Rotating Anode

How to rotate the Anode:

How to rotate the Anode

Grid controlled X ray tubes:

Grid controlled X ray tubes Contains its own ‘switch’ – allows X rays to be turned on and off

Saturation voltage:

Saturation voltage Above a certain saturation voltage, the space charge effect, theoretically has no influence on current flowing in the X ray tube

Heel effect:

Heel effect Intensity of the X ray beam that leaves the tube is not uniform throughout all portions of the beam It depends on the angle at which the X rays are emitted from the focal spot

Tube Shielding and High voltage cables:

Tube Shielding and High voltage cables Tube housing absorb primary and secondary x rays Provides shielding from high voltages required to produce X rays

Electron orbits and energy levels:

Electron orbits and energy levels Binding force – potential energy Kinetic energy Electron movement to a lower energy shell – emission of energy – photon Forbidden transition

Interaction of Electron beam with X ray tube target:

Interaction of Electron beam with X ray tube target

General Radiation:

General Radiation

Characteristic Radiation:

Characteristic Radiation

Intensity of X ray beams:

Intensity of X ray beams Target material Voltage applied Tube current Filtration

To summarize..:

To summarize.. X rays are produced by energy conversion when a fast-moving stream of electrons is suddenly decelerated in the target of an X-ray tube An X ray tube is a specially designed vacuum diode tube. Heat production in the tube is minimized by using the line focus principle and a rotating anode

To summarize..:

To summarize.. X rays are generated by two different processes Production of a continuous stream of X rays ( Bremsstrahlung ) Characteristic X rays Quanity of X rays generated is proportional to Atomic number of the target material (Z) Square of the kilovoltage ( kVp ) 2 Current of the X-ray tube Quality of the X rays generated depends almost entirely on the X ray tube potential

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