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51 Cards in this Set
- Front
- Back
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Who invented the Coolidge hot cathode vacuum tube? |
Dr. W.D. Coolidge in 1913 |
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When was the recessed PID first introduced? |
1966 |
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What year did the gvt. begin regulating the manufacture and installation of all dental xray machines? |
1974 |
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What are the 3 parts to the dental x-ray machine? |
control panel extension arm tube head |
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Control panel |
contains the regulating device |
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Extension arm |
or bracket- enables the tube head to be positioned |
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tube head |
contains the x-ray tube from which xrays are generated |
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Electric current |
enters the control panel through a cord plugged in outlet or via direct connect to power line in wall |
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What are the 5 major controls on dental xray machines? |
line switch milliampere selector kilovoltage selector timer exposure button |
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Line Switch |
On/Off button |
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Milliampere selector |
measures the amount of current passing through the wires of the circuit determines the available number of free electrons at the cathode filament= # of xrays that will be produced |
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Kilovolt peak selector |
determines the speed of electrons traveling toward the target on the anode and therefore the penetrating ability of the xrays produced |
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Timer |
regulates the duration of the interval that the current will pass through the xray tube fraction of a second or impulses 60 impulses in one second |
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Exposure button |
activates the xray production |
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dead-man exposure switch |
automatically terminates the exposure when the operators finger ceases to press on the timer button |
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What does the tube head contain |
lead lined housing dental xray tube insulating oil step up and step down transformers |
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What are functions of the tube head metal housing |
protect the xray increases safety of machine by grouding contents to prevent shock prevents overheating lined with lead to absorb xrays |
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Electrical circuit |
the path the electricity flows |
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Filament circuit |
provides low voltage (3-8 V) to the filament of the xray tube to generate electrons needed for xrays |
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High-voltage circuit |
provides 60-100 kV necessary to accelerate electrons from the cathode filament to the anode target |
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Transformer |
an electromagnetic device for changing the current coming into the dental xray machine Located in tube head step up step down |
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Step down transformer |
low voltage decreases voltage from the wall outlet to approx. 5 volts just enough to heat the filament and form an electron cloud |
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Step-up transformer |
high voltage increases wall outlet to approx. 60-100 kVp to propel the electrons toward the target begins to flow through the cathode-anode circuit when the exposure button on the line switch is depressed |
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Autotransformer |
located in control panel voltage compensator corrects minor fluctuations in currents |
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Amperage |
measurement of the number of electrons moving through a wire conductor |
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Voltage |
measure of electrical force that causes electrons to flow through a conductor |
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Ampere (A) |
unit of quantity of electric current increase= more electrons more xray dental xray range: 4-15 MA |
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Voltage (Volt) |
the electrical pressure (potential difference) btw two electrical charges determines the speed of electrons when travelling from cathode to anode determines penetrating power of xrays |
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What is a high level of voltage called? |
kilovolt equals 1000 V |
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Polychromatic beam |
xrays of many different energies produced by voltage |
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Kilovolt peak |
the highest voltage to which the current in the tube rises range on dental xray 60-100kVp |
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What are 3 conditions that must exist for xrays to be produced? |
1. an available source of free electrons 2. high voltage to impart speed to the electrons 3. a target that is capable of stopping/slowing the electrons |
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Xray tube |
a glass bulb from which the air has beeen pumped to create a vacuum |
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Negative electrode |
cathode |
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Positive electrode |
anode |
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What is the purpose of the cathode? |
to supply the electrons necessary to produce xrays |
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What does the cathode consist of? |
a thin spiral filament of tungsten wire |
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filament wire |
when heated to incandescence (red hot glowing) produces electrons aka thermionic emission |
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Electron cloud |
formed when thermionic emission occurs in the cathode |
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focusing cup |
wire filament is recessed in cup
focusing cup directs the electrons toward the target on the anode |
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What controls the thermionic emission and therefore the quantity of free electrons available? |
milliamperage |
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What is the purpose of the anode? |
to provide the target to stop or significantly slow the high-velocity electrons converting kinetic energy into xrays (electromagnetic energy) |
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What is the anode made up of? |
a copper bar with a tungsten plate embedded in the end that faces the focusing cup of the cathode |
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What is another name for the tungsten plate |
the target set at an angle of 20 degress on the anode |
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Primary beam |
xray produced at a 20 degree angle on tungsten plate |
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focal spot |
a small rectangular area on the target of the anode to which the focusing cup directs the electron beam |
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Primary beam |
the useful beam the original originates at the focal spot and emerges through the port of the tubehead |
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Polychromatic |
consisting of various wavelengths example: xray beam |
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Intensity |
the product of the number of xrays(quantity) and the energy strength of the xrays (quality) per unit of area per nity time |
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What affects density |
milliamperage kilovoltage exposure time distance |
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Keep |
Going, youre a star! |
