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Physics 2 unit 2
| Question | Answer |
|---|---|
| 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 |
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atesta0824
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