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Physics Chapter 6

X-ray tube components and tube failure/ tube charts

QuestionAnswer
Explain the protective housing of the X-ray tube lead lined and surrounds the tube to prevent leakage radiation.
What does the xray protective housing protect from? protects against electrical shock. Provides mechanical support Contains oil that serves as an electrical insulator and thermal cushion
Metal/Glass Envelope has two diodes, name them.. Cathode (filament) Anode (target)
What is the purpose of the metal/glass envelope? to maintain a vacuum. The production of xrays would be less efficient without it because the electrons would interact with the particles in the air.
Gassy Tube filled with air molecules because the tube vacuum has deteriorated
Internal structure of the X-ray tube Filmanet and Focusing Cup
filament coil of wire approx. 2 mm in diameter. 1-2 cm long
focusing cup metal cup that the filament is embedded in.
filament circuit when tube is on a low current passes through filament, preparing it for an exposure.
Space Charge Effect cloud of electrons around the filament that becomes so large that it makes it difficult for additional electrons to be boiled off.
Dual Focus Tube come with two focal spots: small and large
Benefits of small focal spot used with mA stations less than 300. Provides better spatial resolution. Don t use all the time because of tube burn out. Better detail, more patient dose.
Benefits of large focal spot used with technical factors that require a lot more xray photons. Less detail, less patient dose.
Anode positive side of the X-ray tubes
2 types of anodes rotating and stationary
rotating anode used for general purpose X-ray tubes because of the high intensity of the xrays that are produced. Moving focal spot, less detail.
Stationary anode used in dental. Very high tube current and power aren't required. Very limited output can heat up and burn out if used for diagnostic xray.
Functions of the anode electrical conductor, provides mechanical support for the target, good thermal conductor.
Anode materials copper, graphite, molybdenum
Target materials tungsten (molybdenum or rhodium for mammography)
Target material characteristics has high atomic number, good thermal conductor has high melting point
line focus principle the effective focal spot size is smaller than the actual focal spot
actual focal spot area on the target that's being bombarded with electrons. It is controlled by the length of the filament
effective focal spot the focal spot that is projected down towards the patient. the actual source of radiation
Anode heel effect xray intensity on the cathode side is higher than the intensity on the anode side.
Extra-focal radiation electrons bounce off of the focal tract and enter and interact with an area outside the focal tract to produce xrays
3 ways heat can be dissipated at the anode radiation, conduction, convection
Causes of tube failure melting or pitting of the anode long exposure timers filament vaporization cracked anode gassy tube
Melting or pitting of the anode temp of the anode is excessive due to exposure exceeding the tube rating chart. Excessive heat can produce many small pitts or melts on the surfaace of the focal tract
Long exposure timers results from maintaining the anode at elevated temperatures for a prolonged exposure time of 1-3 seconds. Anode will seize up and quit rotating.
Filament Vaporization causes tungsten to vaporize and deposit itself on the inside of the envelope.
Cracked Anode single, large exposure to a cold anode causes it to rapidly heat and crack
Gassy tube tube vacuum deteriorates allowing air molecules in causing the electrons from the cathode to interact with air molecules and decrease tube output..
Created by: 671470335