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Physics 2 unit 2

Thermionic diode consists of what a cathode and an anode
What is the negative terminal called a cathode
This is also called a filament a cathode
What is the positive terminal called an anode
This is also called a target an anode
What does the housing of the x-ray tube do serves to provide protection from radiation exposure and electric shock
In radiation exposure x-rays are emitted how isotropically
What is the maximum allowable leakage in the housing of radiation exposure 100mR/hr @ 1 meter
What is the contructionj of a glass envelope Large vacuum tibe and window
only useful x-rays pass through this part of the x-ray tibe window
Old tube is called Crookes tube
Which tube has gas in it Crookes tube
The basis for modern tube is called Coolidge tube
What are the three main parts of the cathode Filament, focusing cup and supporting wires
What is the filament made of thoriated tungsten
What is thoriated tungsten Tungsten plus 1-2% thorium
Tungsten"____ ____" on of the glass envelopes plates out
What happens to diameter of the filament with age it will decrease causing more resistance of the filament
If the diameter of the filament decreases what happens to the tube current increases
The plating out of the filament and the increased resistance will offset each other
What is the purpose of the filament to provide electrons in the tube
What is the focusing cup made of a metal cup with a negative charge placed on it
The effectiveness of the focusing cup is determined by what four things 1.size and shape of the focusing cup 2. charge 3. filaments size and shape 4. positioning of the filament in the focusing cup
Space charge does what to thermionic emission hinders it but increasing the kVp will overcome it
A filament current is 3-5amps
A small increase in filament current causes a dramatic increase in the thermionic emission
Dual focus tubes are large focal spot, small focal spot, and fractional focal spot
The large focal spot is 1.00mm-2.5mm
small focal spot is .3mm-1.00mm
fractional focal spot is less than 0.3mm
2 types of anodes are stationary and rotating
This has a small button of copper with tungsten imbedded in it stationary anode
Thses are composed of tungsten Rotating anode
The newer rotating anode tubes consists of molybdenem disk coated with a tungsten-rhenium alloy
What does rhenium do to the focal spot diminishes the roughening of the focal area which maintains a high output also called emissitivity
What are the three functions of the anode electrical conductor, mechanical conductor, thermal conductor
the target or anode is made of tungsten
what are the 3 reasons tungsten is used high melting point, good conductor of heat, good conductor of electricity
In the rotating anode what are the two induction motors called stator and rotor
electromagnetic is a stator
soft iron is a rotor
What is the average RPM in a rotating anode 3,400-3,600
Special high speed motors(rotating anode) measures 10,000 rpm(used in special procedures)
What are wobbly anodes noticed by consistent unsharpness(when all other fators are ok), increased noise or vibration from the tube and short coast time
This is when crators or holes form in the anode pitting
Pitting can cause what a 20% reduction in x-ray output and geometric unsharpness
You should never use what kind of anode a cold one
What should the warm up of an anode be 1/10 of the heat units of what would be produced by the first diagnostic exposure
As mA is increased what happens in the focal spot blooming
What do we use to measure a focal spot pinhole and star pattern
What is themm for a pinhole camera >0.3mm
what is the mm for a star pattern <0.3mm
What is the projection of an inclined line into a surface resulting in a smaller area line focus principle
What is the purpose of the line focus principle to give us heat capacity of a large focal spot and the geometric sharpness of a small focal spot
This is the area projected onto the patient and the image receptor effective focal spot
This the are bombarded by electrons actual focal spot
what is the largest of the two focal spots actual focal spot
The average target angle is 5 to 20 degrees
The smaller the target angle is the___ the effective focal spot size smaller
The selection of the overall tube depends on the overall work load
The average room see how many patients, does how many exams, and takes how many exposures 25, 37, 148
What is the most likely result from slightly exceeding the safe operation of the x-ray tube for an exposure? Reduction in tube life
What is the most likely result from greatly exceeding the safe operation limit of the x-ray tube? Pitting of the anode
What can happen to the x-ray tube due to overheating the anode? Tube can become gassy
Increasing mA or kVp will produce a smaller load on the anode? kVp
You should always know the safe limits of your x-ray tube for _____, ______ and _______. mA, Time, kVp
Unique Tube rating charts are developed according to: 1) Type of rectification 2) Size of the focal spot 3) Tube design 4) Power Supply 5) Cold vs. Hot tube (most are for cold tube)
The ability of the anode to store heat is measured in ______ ______ Heat Units (HU)
Formula for finding Heat Units: 1) Single Phase 2)3 phase, 6 pulse 3)3 phase, 12 pulse 4)high frequency 1)mA x time x kVp 2)1.35(mA x time x kVp) 3)1.41(mA x time x kVp) 4)1.41(mA x time x kVp)
What changes can be made to lower the heat units? Higher kVp and lower mAs
Created by: atesta0824