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RAD 231 unit 2 proto
| Question | Answer |
|---|---|
| the purpose of the cathode focusing cup is too: | group the electrons for the passage to the anode |
| The mostly widely used support structure for the x-ray is: | ceiling support system |
| The protective housing of the x-ray tube helps to: a.keep the x-ray tube cool b.prevent electrical shocks to the radiographer c. limit leakage radiation d.all of the above | d.all of the above |
| The heel effect is caused by the: | anode angle |
| The _______________ is/are component(s) outside the glass envelope. | stators |
| The purpose of the cathode focusing cup is to: | group the electrons for the passage to the anode |
| High capacity tube rotors revolve at ______ rpm. | 10,000 |
| During the prep portion of the x-ray exposure: | the anode begins rotating and the filament heats up |
| The autotransformer has _________ winding(s). | One |
| Radiation that is produced in areas of the target other than the focal spot is called: | extrafocal |
| A step-down transformer is located in the ____________________ circuit. | filament |
| As the x-ray tube ages and filament evaporation occurs, for a desired tube milliamperage, a progressively: | lower filament current is required |
| The most accurate exposure timer for the shortest exposure time is the: | Electronic Timer (Modern Type) |
| Electric insulators: | inhibit the movement of electric charge |
| Which section of the x-ray tube circuit conducts milliamperage? | Secondary circuit |
| The goal of the filament circuit is to: | Heat the filament wire located in the cathode |
| A dual focus tube has two: | filament |
| To extend x-ray tube life, the technologist should: 1. perform warm-up exposures a the beginning of each day 2. avoid boost and hold method unless necessary 3. avoid repeat exposures at or near the tube's capacity | 1, 2 |
| Used during the 1870s and 1880s - Cold cathode gas tube -Partial vacuum -inefficient | Crooke's tube |
| Process where air is removed not only from the interior of the tube, but from the glass and metal parts as well, by prolonged baking before the tube is sealed | Degassing |
| A high vacuum is necessary for two reasons: | - to prevent collision of the high speed electrons with gas molecules, which would cause slowing of electrons - To prevent oxidation and burning out of the filament |
| Improvement from the crookes tube, where vacuum was first introduced. manipulation of kVp and mA levels independantly. AKA hot | Coolidge tube |
| Tube componenents are sealed in a vacuum to permit electrons to travel freely from ______ to ______ | cathode (negative) to anode (positive) |
| For a C-arm system the intensifer is located on ____ | top |
| This type of enclosure holds the x-ray tube electrodes cavuum sealed and immersed in insulating oil (cooling & prevent spark over) | Glass (Pyrex glass) tube enclosure |
| A disadvantge of glass envelope is? | deposits due to evaporation of tungsten reduces tube life |
| Regulation require leakage radiation below ____mR/H at 1 meter from the tube | radiation below 100mR/h at 1 meter from the tube |
| A negative charged concave metal cup behind the filament confines the electrons to a narrow beam and focuses them as the ____ on the tungsten target. Aka the anode region where the projectile electrons strike | Focal spot |
| The filament current, serving to heat the filament and provide a source of electrons within the tube, usually operates at about _____ volts and ____ to ___ amperes | operates at about 10 volts and 3-5 amperes |
| Loss of metal (tungsten) by evaporation causes the filament to become progressively thinner. called? | Thinning of the filament |
| Thinning of the filament is ____ proportional to electral resistance. As cross-section of the wire decreases then it increases resistance. filament = hotter tube current/mA increases - RE increases | Inversely |
| vaporized tungsten deposits on the internal wall of the galss tube, this acts as an additional filter, reducing xr output. Being that the tungsten deposits are metal, it attracts electrons from the stream, eventually puncturing the glass. | Deposition of tungsten on the glass envelope |
| component of the tube, negatively charged electrode, functions to produce thermionic cloud, conducts high voltage to the space between the cathode and anode. consists of two filaments, focusing cup, supporting wires | Cathode |
| What are the supporting wires of the Cathode? | One brings current (3-5 amps) to the select filament wire Second brings voltage (10-12 Volts) Third brings high voltage negative charge to cathode |
| What is the atomic number of tungsten? | 74 |
| What is the atomic number of thorium? | 90 |
| Is responsible for heatin the filament up to the temperature that corresponds to the mA station selected for exposure | Filament current |
| Boiling off electron by heating the filament wire to incondescent | thermionic emission |
| effect happens when electrons reach a point where their negative charges begin to oppose the emission of additional electrons. Limits the xr tubes to maximum mA ranges of 1000 to 1200. | Space charge effect |
| When sufficient mA is applied, the electrons begin to build up into a cloud around the filament; this is called a | space charge |
| is made of nickel and molybdenum with two depressions that contain the filaments. | Focusing cup |
| Electrons with their negative charge tend to diverge in a wide pattern because of | electrostatic repulsion |
| a low ____ charge on the focusing cup surface forces the electron cloud into a narrow beam. | low negative charge |
| The attration of photons to the tungsten deposits on the glass envelope is called | Arcing |
| The addition of ___ slows down the degrading of tungsten | thorium |
| ____ circuit applies kVp (tube current) at the 2nd dperession of button | secondary circuit |
| the first depression of the button ____ the wire | rotors and heat the wire |
| Under ___ kVp then 100% are brems | 70 kVp |
| Over 70 kVp then ____ brems and ____ characteristics | 85% brems and 15% characteristics |
| Such an anode is used in dentistry. gap of a few cm separates the cathode from anode which consists of a block of copper. Disadvantage is it has a low heat capacity; which means you cant do a lot of exams back to back | Stationary anode |
| Automatic adjusts filament current to maintain constant mA over a wide range of kV Lowers filament current as kVp is raised to keep mA constant over the kV range. | Space charge compensator |
| a ___ (sml/Lrg) focal spot size creates sharper images | smaller |
| A situation w/o the space charge compensator where increasing kVp drives more electrons to the anode - increases mA. Undesirable b/c kVp cannot be changed independently of mA | Space-charge limited region |
| A situation w/o the space charge compensator where mA is not influenced by kVp and only influenced by temp of filament. Further increase in kV cannot increase mA; the portion of the curve is flate representing this: | Saturation current/ temperature limited region |
| The larger the filament current (measured in amps), the (greater/lesser) will be the resulting mA. | Greater |
| Primarily in portables, One filament, has 3 electrodes. Has a biased focusing cup. Focusing cup acts as a switch to start and stop exposure. | Grid controlled tubes |
| bias focusing cup is kept at a more negative voltage than filament. kV range of ____ is automatically applied and wave-tail cuttoff is achieved. | -1 - 2 kV |
| Process of stopping the discharge of the capacitor at some preselected point on the discharge curve | wavetail cuttoff |
| Tungsten has a melting point of? | 3370 degrees celcius |
| __% heat production, __% x-rays | 99% heat productive, 1% x-rays |
| a thin layer of ______ is used on top of molybdenum because it prevents distortion of metal. | tungsten - Rhenium alloy |
| This can store 2x more heat than tungsten. It is less dense making it easier to rotate the anode without increasing wear on the bearings. | Molybdenum - Z = 42 |
| An advantage of a roating anode compared to a stationary is? | greater heat capacity (tube rating) |
| is described by the area on the focal track that is impacted by projective electrons. It is determined by the length of the filament and the width of the focusing cup depression. | Actual focal spot |
| describes the area of the focal spot that is projected out of the tube in a downward path toward the object being imaged. Smaller this will increase SR | effected focal spot |
| type of motor that operates on alternating current that forces the rotor to follow the external magnetic fields of the stator, thereby pulling the rotor to the next position. | Induction motor |
| w/in a induction motor, both the ____&____ are sealed inside an evacuated glass envelope. The _______ located outside is supplied w/ alt current, which produces changing mag fields by switiching the current in each set of electromagnets. | Rotor and anode are sealed inside; Stator is located outside |
| Prolonged witholding exposures can cause premature tube destruction. Many tech allow too much time to elapse btwn activating the rotor control and exposure control button. | Boost and hold |
| angling or slanting of the target face to provide a large area for heat distribution (acutal fs) but a small area to assure image sharpness (effective fs) | line focusing principle |
| an increase in anode angle will (increase or decrease) effective focal spot size? | increase (vise versa) |
| A anode angle less than 45 degrees will improve SR. aka a smaller target angle results in a smaller effective focal spot size and better detailed images. If it is greater or equal to 45 degrees than it will be _____. | identical |
| A small anode target angle, (increases or decreases) anode heel effect and tube rating? Vise versa | increases |
| According to the anode heel effect, the highest intensity (quantity) is on the ____side. because it has to go through more mass(rotor) | cathode side |
| T/F placing the cathode side on parts that are thinner, such as cerv vs thorax, makes the image look burnt out. | True; Thinner side should be on anode side. |
| The main cause of tube failure is? | Spark over(arcing) : puncture of glass envelop |
| Filament can burn out from normal use or from _____ such as from boost and hold. | excessive current. |
| Which wave has a higher tube rating, a 3 phase or single? | 3 phase |
| Tube rating depends on? | 1. type of rectification 2. tube focus size 3. tube design 4. type of power supply 5. temperatore of tube 6. application |
| Heat unit is calculated by? | multiplying kVp, mA, time(seconds), correction factor, and number of exposures |
| Single phase has a correction factor of? | 1 |
| Three-phase, 6-pulse; three-phase, 12 pulse & high frequency unit has a correction factor of? | 1.41 |
| an increase in the actual area of the focal spot or track (increases or decreases) the instaneous rating of the anode, wheras an increase in the anode mass (increases or decreases) its thermal capacity. | an increase in the actual area of the focal spot or track increases the instaneous rating of the anode, wheras an increase in the anode mass increases its thermal capacity. |
| an increase in anode mass = (increase or decrease) in thermal capacity? | increase |
| an increase in area of focal spot or track = (increases or decreases) instantaneous rating? | increases |
| Higher kVp techniques produce (more or less) heat? | Less |
| 3 types of tube rating charts? | 1. radiographic tube rating chart 2. anode cooling chart 3. house cooling chart |
| in a XR tube rating chart, any point on or above the line is safe or unsafe? safe meaning the exposure will not exceed the instaneous rating of teh tube and will not overheat it. | unsafe |
| Tells how long the anode must cool in between exposures | anode cooling curve |
| Tells how long it takes to cool the housing before additional exposures can be made. | Housing cooling chart |
| A typical warm-up procedure would consist of? | two 70 kVp w/ several low mA long exposures and 2 sec exposures. |
Created by:
Btran573