X-Ray Tube.pptx

X-RAY TUBE AND PRODUCTION OF X-RAYS IS DESCRIBED IN DETAIL IN THIS PPT.
CONTENT TAKEN FROM MULTIPLE BOOKS AND JOURNALS.

1. X-Ray tube Mr. Rohit Bansal Assistant Professor (Radio-physics)

2. Content Introduction History Principle of x-Ray tube Types of x-ray tube Components of xray tube Production of xrays

3. Xray tube is a device meant for Xray production. Introduction An x ray tube is a vacuum tube
Contains a pair of electrode i.e cathode and anode
Cathode contains filament that releases electrons when High voltage is applied
Anode is made up of tungsten which attract the electrons
When the electrons released from the cathode come in contact with the tungsten they release energy in the form of photons
These high energized photons are channelled through a lead cylinder and series of filters grating of X rays

4. History XRAYS were discovered by Sir WC Roentgen on Friday 8th November 1895 in Germany • At the time of discovery he was experimenting about cathode rays when he passed current through crooks type tube covered with card board shield to stop any light arising from the fluorescence of glass walls in a dark room. He was surprised to note small glow coming from near placed sheet of paper painted with barium platinocyanide .He confirmed these emanation of rays coming from the tube and named them XRAYS.

5. Principle Xrays tube is a device based on the principle of energy conversion When the fast moving electron comes in the vicinity of the heavy nucleus it gets attracted towards the positive charged nucleus due to Columbic force and gets deviated from its original path . In this process kinetic energy of fast moving electron is lost and converted into heat(99%) and X-Ray energy (1%).

6. History and development of xray tube 1895: X-rays were discovered from experimental discharge tube called as Crooks tube or Cold cathode tube. In 1913: Crooks tube was improved by William Coolidge c/as Coolidge tube or Hot cathode tube. In 1915: Hooded anode tube. In 1920: Oil cooled tube. In 1929: Rotating anode tube. In 1932: Grid controlled stationary anode tube In 1937: Grid controlled rotating anode tube. In 1959: High speed tube.

7. Cont.... In 1962: Rhenium alloyed tungsten composite anode tube. In 1967: Mammography unit with Mb anode. In 1971: Glass metal tube with Mb anode. In 1973: Three layer anode tube. In 1979: Metal ceramic tube. In 1981 : Three focus tube. In 1989: Direct anode cooling with noiseless rotor. In 1989: Introduction of helical CT ube ( by Sienmens). In 1990: MRC tubes ( Maximus rotalix ceramic) by Philips.

8. Cont..... In 1998: Development of grid control rotatingAngiography X-tay tube cooporaled with PuliseFuoroscopy applicable cathodeanode for angiography by Toshiba. In 1999: Double focus stationary anode x-raytube for mobile c-arm. In 2000: Food inspection x-ray tube. In 2002:High speed rotation bearing rotatinganode tube for angiography. In 2003: Micro-focus X-ray tubewith power supply used forinspection technology. In 2006: there is introduction of STATRONx-ray tube by Siemens.

9. Types On the basis of cathode Cold Cathode Tube ( Crooke’s tube)/(Gas Discharge tube) Invented by British physicist William Crookes in early 1870. Crookes tube also called cold cathode to because they do not have a heated filament in them that release electron Early X-Ray tube called as gas tube because :- Its action depends on the presence of small residual amount of gas present in it and the radiographer kept a selection of tubes of various mAs values on a reck . When the change in mAs was required the radiographer disconnected the tube and replaced it with different one.

10. Components Cathode is on the right anode is in the centre with attach heat sink at left. The device at the top is a softener used to regulate the gas pressure. An aluminium cathode plate having curved shape to created the beam of electrons. A platinum anode target to generate Xrays.

11. Limitations Low output Unstable X-Ray production. This tube cannot produce x- rays continually. We cannot operate the kVp and the mAs independently as there is presence of gases.

12. 2. Hot cathode tube ( Coolidge tube ) The coolidge tube was improved by William Coolidge in 1913 . In the coolidge tube electrons are produced by thermionic effect (on heating metal element emit electrons). It permitted:- Greater flexibility in the quality and quantity of X-Ray produced . Greater tube stability during the production of X rays. Smaller tube size. Longer tube life. Coolidge tube is the prototype of modern X rays tubes being used today. An early problem with this mode cathode to the conduction of heat away from the tungsten target.

13. 2. On the basis of Anode Stationary Anode Tube Anode is stationary. Small focal spot area. Low heat loading. Mostly used in dental unit and portable machine. Rotating AnodeTube Anode rotate at very high speed. Large focal spot area. High heat loading capacity. Mostly used in diagnostic machine.

14. Components of MODERN xray tube Tube support Glass envelope Cathode Anode 5.Protective housing

15. 1. Glass Enevlope The glass envelope is made up of pyrex glass. The envelope maintains a vacuum inside to to allow more efficient Xray production and longer tube life. The primary function of envelope is to provide support and electrical insulation for anode and cathode assemblies. At point where primary Xray beam exit glass is thinner.

16. 2. Tube support Xray tube and housing assembly are quite heavy and therefore require a support mechanism so that the radiologic technologist can position it. There are 3 methods of X-Ray tube support :- Ceiling support system Floor to ceiling support system C-arm support system

17. Ceiling support system The ceiling support systemis probably the mostfrequently used. It consistofof 2 perpendicular sets ofceiling-mounted rails. This allow for both longitudinal and transverse travel of the x-ray tube.

18. Floor to ceiling support systEm The floor to ceiling support system has a single column with rollers at each end and one attached to a ceiling mounted rail and other attached to a floor mounted rail. The tube slides up and down as a coulmn rotates

19. C-Arm support system Interventional radiology suites of an hour are equipped with c-arm support system so called because the system is shaped like a letter c .These system are ceiling mounted and provide for very flexible x-ray tube positioning .

20. 3. Cathode . It is the negative electrode of the X-ray tube .It consist of a metal structure to support the filament. :It consists of Filament source of electrons Connecting wires which supply the voltage about (10 volt )and current (3 to 5 A). Metallic focusing cup.

21. Filament Cathode filament made of thin tungsten wire which is a source of electrons. It works on the phenomena of thermionic emission. Tungsten spiral wire of diameter 0.2 mm. Length 1.0 cm. Diameter of spiral 0.2 cm.

22. Tungsten Tungsten is used as filament material because of following reasons:- It has a high melting point of 3370 degree Celsius Less tendency to vaporize. High tensile strength means it can be drawn into wires. High thermal conductivity and specific heat. Appropriate threshold or work func tion.

23. Focusing Cup It is a device surrounding the cathode filament in the Xray tube. This is actually a third electrode in the tube called a wehnelt electrode. Because of the forces of mutually reversion of a large number of electrons this electron stream would tend to spread itself out and result in a bomb bardment of large area on the anode of Xray tube. This is prevented by focusing Cup which surround the filament. If this electrode is not present the electrons wood heat the anode over a large very large area. It is usually made up of nickel because of:- Light weight Poor thermal conductivity High melting point.

24. 4.Anode It is a positive electrode of X-Ray tube. It consists of a target (focus spot) and cylindrical copper block or tungsten. Made up of a small plate of tungsten 2 or 3mm thick that is embedded in a large mass of copper. Square or rectangular in shape with each dimension usually greater than 1 cm. We use tungsten as a target material because of the following reasons:- High atomic number( 74). High melting point( 3370`c ) High thermal conductivity. It does not vaporize easily.

25. Target material Target material is based on the three characteristics:- Atomic number: - must be high so that it results in a high efficiency in X Ray production Thermal conductivity:- must be able to conduct heat away from the target. High melting point:- must be able to withstand high temperature.

26. Focal spot It is the area actually bombarded by electron stream on the target. It can be larger or smaller in size. Small focal spot is required for producing good radiographic detail but it may also lead to overheating of target. Where as large focus port allows greater heat loading but does not produce sharp image. This problem was solved in 1918 by the development of line focus principle.

27. Line focus principle Explain the relationship between actual focal spot on the anode surface and the effective focal spot size. It states that the effective focal spot is smaller than the actual focal spot. By angling the face of anode target a large actual focal spot size can be maintained and a small effective focal spot can be created. Typical anode angle 6- 20° . Advantages:- Provide small effective focal spot for good radiographic details. Provide large actual focal spot for greater heat loading.

28. Types of Anode Stationary Anode lt is a solid bar of copper with an insert of tungsten on the face of bar opposite the cathode filament. Advantages:- compact unit Low cost Limitations:- since area covered by electrons beam on the target for example x-ray source and the area over which heat is supplied are the same so we cannot use higher electrical loads or high mAs. Application:- dental x-ray sets small portable and mobile X units with limited output.

29. Rotating anode An Xray tube in which the anode rotates when Xray are being produced. This means that there is a larger effective target surface of anode which can be able to generate the X-rays. Constructed of tungsten target , molybdenum and graphite.

30. 5. Protective Housing The Tube housing function is to containing and supporting the Xrays tube and oil and protecting them from external damage. The metal tube has two other important function to perform:- Firstly it it provides a completely and encircling metallic shield because it is firmly connected electrically to earth potential protects the user from any possibility of electrical shock. The second purpose of tube shield is to afford protection to radio grapher and patient against unwanted radiation. It is arranged that an Xrays ( both primary and secondary ) which are not within the wnated beam are attenuated by sheild.

31. Production of xrays Xrays are produced by energy conversion when a fast moving stream of electron is suddenly be accelerated in the target anode of xray tube. Electrons produced at cathode can be accelerated by a high potential difference towards anode. Electron produced by heated tungsten filament and accelerated across tube to hit the tungsten target where Xrays are produced. Fast moving electrons are suddenly stopped by impact on the metal target. High speed electron lose energy by two processes :- Reaction of electrons with nucleus of tungsten atoms. Collision between high speed electron and electrons in the shell of target tungsten atom.

32. Types of xrays When a high speed electron lose energy in the target of Xray tube two processes of xray generation occcur :- General radation/ Bremsstrahlung radiation. Characteristic radation.

33. Bremsstrahlung radIation When an electron pass near the nucleus of tungsten atom the positive charge of nucleus acts on negative charge of electron. The electron is thus deflected form its original position. Electron may lose energy and slows down when its direction changes. The kinetic energy lost by electron is directly emitted in the form of photon radiation. The electron only gives up part of its energy in the form of radiation - braking radiation. Wavelength of radiation produced depends on energy of electron and the potential difference .

34. Characteristic radation The electron bombarding the target eject electron from the inner orbit of target atom. Removal of an electron from the tungsten atom causes the atom to have an excess positive charge :- a positive ion. In the process of returning to its normal state the ionized atom of tungsten may get rid of excess energy in two ways :- An additional electron may be expelled by the atom and carry excess energy (there is no x ray production in this way) The atom emits radiation that has a wavelength in the range of diagnostic X-rays called characteristic Xrays.