Lesson 9&10 Flashcards
What are the xray generating apparatus?
°1. ELECTRICITY
°2. ELECTRICAL CURRENT
°3. ELECTRICAL CIRCUIT
energy to make xrays
associated with presence and flow of electric charge or electrons around a circuit
ELECTRICITY
flow of electrical energy / electrons through a circuit measured in amperes
ELECTRIC CURRENT
path of electrical current
ELECTRICAL CIRCUIT
What are the flow of current in 2 phases?
1 positive phase
1 negative phase
first half-cycle
(positive phase)
•second half-cycle
(negative phase
First half cycle current
flows; ______ produced
x-rays
second
half-cycle> no _________; no x-
ray production.
current flow,
therefore, in xray production
There is a change in polarity of the anode
and cathode that occurs
6ox /sec
Reverse voltage
•60-cycle AC
l
• 6o pulses of x-rays emitted every second
l
• Duration: ______ sec
1/120
**rays are produced in the form of______
impulses
•the tube does its own rectification
SELF-RECTIFICATION
type of power that limits xray production to half of the AC cycle
halfwave rectification
2 electrical circuits for ray production:
- Filament circuit
II. Anode-cathode circuit
- on-off switch
- mA control
- step-down transformer
Filament or low voltage circuit.
Anode-cathode or high voltage circuit
- kVp selector
- timer
- activating button
- x-ray emission light /
sound OR indicator button - step-up transformer
> length of time to produce xrays
controlled by the timer
Exposure time
> Expressed as:
fraction of a second
whole numbers of seconds
impulses per exposure
Exposure time
Formula to determine exposure time in seconds:
no. of impulses
——————— = exposure time in seconds
60
Formula to determine exposure time in impulses:
exposure time in sec X 6o = exposure time in impulses
2 terms to regarding number of electrons and electrical force:
• 1. amperage
- Voltage
measure of the amount of electrical current flowing through a circuit
amperage
- 8 to 15 mA
- adjusted with the mA selector
amperage
measurement of electrical force needed to move electrons from a (-) to(4)
electrode
Voltage
65 to 95 kV or 65,000 to 95,000volts
Voltage
kVp = highest voltage to which rays are
produced
Voltage
True or false
mAand voltage affects quality of the ray beam
True
HEAT - 99%
X-RAYS- 1%
Tube interactions
True or false
X-ray beam is a solid beam
False
(X-ray beam is NOT a solid beam)
True or false
Electrical energy is converted to x-ray energy
and heat
True
True or false
Millions of high-speed electrons from the cathode interact with uncountable numbers of tungsten atoms at the target. The sudden stopping of the electron motion causes kinetic energy of the electrons to EM energy
True
True or false
The millions of x-rays produced are of same wavelengths and energies
False
(The millions of x-rays produced are of different wavelengths and energies)
2 mechanisms that explain
X-rays Production at the Atomic Level
°A. General Radiation
•B. Characteristic Radiation
•General rays that are produced can have any energy level depending on the kVp value that is used.
X- ray energy
•General rays can be produced at any kVp
X- ray energy
*Characteristic rays need at least 70 kVp to be produced
Xray energy
General rays have a range (______) of energies and form a _____ spectrum (contains all possible values
heterogeneous, continuous
Characteristic rays have a specific energy (_______) and form a ____ spectrum (contains only specific values)
homogenous, discrete
forms of energy associated with the flow of electrons
ELECTRICITY
True or false
ELECTRICAL CURRENT is measured in amperes or milliamperes
True
→ electrons go in one direction through the conductor
→ ex.: batteries
→ current is a steady constant
electrical charge
Direct Current (DC)
electrons go in two opposite directions
Alternating Current (AC)
current alternates between positive and negative, resulting in a voltage waveform shaped like a sine wave
Alternating Current (AC)
shaped like a sine wave
Alternating Current (AC)
True or false
A dental x-ray machine works with 60-cycle AC
True
True or false
A dental x-ray machine works with 110 volts (220 in the Philippines) (self-rectified)
True
True or false
electrical current changes flow 60 times/sec
True
What phase?
current flows
Positive Phase
What phase
→ anode has a positive charge
→ x-ray is produced during this cycle
Positive Phase
What phase?
→ anode has a negative charge
Negative Phase
What phase?
no current
Negative Phase
What phase?
no x-ray produced
Negative Phase
True or false
When the current alternates and becomes a negative charge, there will be no current flow and x-rays will not be produced.
Therefore, in x-ray production, there is a no change in voltage of the anode and cathode that occurs 60 times per second.
False
When the current alternates and becomes a negative charge, there will be no current flow and x-rays will not be produced.
Therefore, in x-ray production, there is A CHANGE IN POLARITY of the anode and cathode that occurs 60 times per second.
no production of x-ray occurs because the anode is negative
INVERSE VOLTAGE/REVERSE VOLTAGE
x-rays are produced in the form of impulses
INVERSE VOLTAGE/REVERSE VOLTAGE
prevents overheating or damage of x-ray tubehead
INVERSE VOLTAGE/REVERSE VOLTAGE
the conversion of AC to DC
SELF-RECTIFICATION
type of power that limit x-ray production to half of the AC cycle
HALF-WAVE RECTIFICATION
(2) electrical circuits are used in the production of x-rays:
o Low Voltage or Filament Circuit
o High Voltage or Anode-Cathode Circuit
lowers incoming voltage from 110-220 volts to 7-10 volts
because it is the only amount of energy needed to heat the
tungsten filament to produce electrons
FILAMENT CIRCUIT
the cathode is the source of electrons for x-ray production
FILAMENT CIRCUIT
provides high voltage required to accelerate electrons and
generate x-rays in the x-ray tube and is controlled by the kilovoltage settings
ANODE-CATHODE CIRCUIT
PARTS OF THE ANODE-CATHODE CIRCUIT
kVp Selector
Timer
Activating Button
selects the kilovoltage applied to the x-ray tube to produce x-rays
kVp Selector
found in a 6 ft. extension cord
Activating Button
expressed as: fraction of a second
EXPOSURE TIME
number of electrons produced
milliamperage
highest voltage to which x-rays are produced whenever a film or radiograph is taken
kVp (kilovoltage peak)
True or false
Amperage and voltage affect the quality of the x-ray beam.
True
STEPS IN X-RAY PRODUCTION
Turn machine on to active step-down transformer and filament circuit
Step 1
STEPS IN X-RAY PRODUCTION
Filament produces electrons
Step 2
STEPS IN X-RAY PRODUCTION
Formation of an “electron cloud”
Step 3
STEPS IN X-RAY PRODUCTION
Exposure button is pressed to activate the high voltage
circuit
Step 4
STEPS IN X-RAY PRODUCTION
Electrons at the cathode are propelled to the focal spot at
the anode
Step 5
STEPS IN X-RAY PRODUCTION
X-rays photons are produced at the focal spot and directed
out of the unleaded glass window to be filtered and collimated (control or change)
Step 6
Step?
The transformer reduces the 220 V to 7-10 V, enough to heat the filament circuit
1
Step?
By heating the tungsten filament in the cathode
portion of the x-ray tube
2
Step?
Thermionic emission occurs, defined as the release
of electrons from the tungsten filament when the electrical current passes through it and heats the lament
2
Step?
The outer-shell electrons of the tungsten atom
acquire enough energy to move away from the
filament surface
3
Step?
The electrons stay in an electron cloud until the
high-voltage circuit is activated
3
Step?
The electrons travel from the cathode to the anode
5
Step?
When the electrons strike the tungsten target, their
energy of motion (kinetic energy) is converted to
x-ray energy and heat
5
Step?
Less than 1% of the energy is converted to x–rays;
the remaining 99% is lost as heat
5
