Lesson 9&10 Flashcards by Love Dog

What are the xray generating apparatus?

°1. ELECTRICITY
°2. ELECTRICAL CURRENT
°3. ELECTRICAL CIRCUIT

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energy to make xrays
associated with presence and flow of electric charge or electrons around a circuit

ELECTRICITY

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flow of electrical energy / electrons through a circuit measured in amperes

ELECTRIC CURRENT

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path of electrical current

ELECTRICAL CIRCUIT

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What are the flow of current in 2 phases?

1 positive phase
1 negative phase

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first half-cycle

(positive phase)

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•second half-cycle

(negative phase

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First half cycle current
flows; ______ produced

x-rays

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second
half-cycle> no _________; no x-
ray production.

current flow,

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therefore, in xray production
There is a change in polarity of the anode
and cathode that occurs
6ox /sec

Reverse voltage

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•60-cycle AC
l
• 6o pulses of x-rays emitted every second
l
• Duration: ______ sec

1/120

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**rays are produced in the form of______

impulses

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•the tube does its own rectification

SELF-RECTIFICATION

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type of power that limits xray production to half of the AC cycle

halfwave rectification

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2 electrical circuits for ray production:

Filament circuit
II. Anode-cathode circuit

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on-off switch
mA control
step-down transformer

Filament or low voltage circuit.

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Anode-cathode or high voltage circuit

kVp selector
timer
activating button
x-ray emission light /
sound OR indicator button
step-up transformer

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> length of time to produce xrays
controlled by the timer

Exposure time

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> Expressed as:

fraction of a second
whole numbers of seconds
impulses per exposure

Exposure time

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Formula to determine exposure time in seconds:

no. of impulses
——————— = exposure time in seconds
60

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Formula to determine exposure time in impulses:

exposure time in sec X 6o = exposure time in impulses

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2 terms to regarding number of electrons and electrical force:

• 1. amperage

Voltage

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measure of the amount of electrical current flowing through a circuit

amperage

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8 to 15 mA
adjusted with the mA selector

amperage

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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

Step? By heating the tungsten filament in the cathode portion of the x-ray tube

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

Step? The outer-shell electrons of the tungsten atom acquire enough energy to move away from the filament surface

Step? The electrons stay in an electron cloud until the high-voltage circuit is activated

Step? The electrons travel from the cathode to the anode

Step? When the electrons strike the tungsten target, their energy of motion (kinetic energy) is converted to x-ray energy and heat

Step? Less than 1% of the energy is converted to x–rays; the remaining 99% is lost as heat