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