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RAD 1126 and RAD 1125 > RAD 1126 CHAPTER 9 > Flashcards

RAD 1126 CHAPTER 9 Flashcards

CHAPTER 9- X-RAY TUBE

1
Q

What are the 3 conditions of x ray production ?

A

1.Free electrons, 2.Acceleration of electrons, 3.Decelerations of electrons

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2
Q

What is space charge??

A

Electrons form a cloud around a filament and it is known as space charge

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3
Q

What is the source of electrons?

A

The heated filament is the source of electrons

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4
Q

How are electrons made?

A

Electrons are accelerated toward the anode by a high-voltage(KVP) POTENTIAL DIFFERENCE AND ELECTROMAGNETIC FORCE (EMF) to a high speed to produce x-rays

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5
Q

What type of charge does the anode aquire?

A

The anode acquires a positive charge to pull the electrons towards it for Deceleration.

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6
Q

What is the size of the filament?

A

small 1 cm Large 2cm

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7
Q

What material is the filament made of?

A

Tungsten alloyed with thorium (thoriated-tungsten)

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8
Q

How many filaments do general purpose x-ray tubes have?

A

It has 2 filament coils, one longer than the other.

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9
Q

What is thermionic emission?

A

When the filament is heated by electricity passing through it, electrons boil off.

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10
Q

What is the process of “boiling off” electrons from the x-ray tube filament called?

A

Thermionic Emission

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11
Q

What charge is the anode?

A

The anode is the positively charged end of the Anode

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12
Q

What is the anode known for being?

A

It is stationary or known for being more commonly rotating

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13
Q

What is the area called which is struck by the electrons?

A

It is the TARGET

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14
Q

The focal spot (actual) on the target is the?

A

It is the actual area where X-rays are being emitted at a moment in time.

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15
Q

What is created when the electrons bombard the target?

A

HEAT & XRAYS ARE CREATED WHEN THE ELECTRONS BOMBARD THE TARGET

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16
Q

How much percent of radiation is useful and how many percent becomes heat?

A

0.5% RADIATION IS USEFUL WHILES 99.5% IS HEAT

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17
Q

What charge is the cathode at the end of the diode tube?

A

It is the negatively charged end of the diode tube

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18
Q

What are the 2 major features of the cathode?

A
  1. The Focusing cup made of Molybedenum or nickel and. 2. The (2 dual focus) filaments
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19
Q

What are the 2 (dual focus) filaments?

A
  1. the smaller filament is about 1cm and 2. the larger filament 1.5-2cm
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20
Q

The filament is chosen when?

A

It is chosen when selecting the small or large focal spot

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21
Q

What is the melting point for filament?

A

The filament has a very HIGH melting point of 6200 degrees Fahrienheit (3400 degrees Celsius)

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22
Q

To focus the electron beam, each filament is embedded within a negatively charged ________ at the cathode

A

Focus spot

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23
Q

the electron beam as it strikes the focal is about ______ the size of the filament from which the electron beam originated

A

1/20th

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24
Q

What causes the electrons to focus such that the focal spot size of 1/20 the size of the 1cm filament at 0.5 - 0.6mm wide and mm in size the large focal spot is 1.0 - 1.2 Some specialized tubes may be as small as 0.1mm.

A

The negative charge on the focusing spot

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25
When the radiographer selects the focal spot setting at the console, what is being selected?
The Radiographer selects the Filament (size) either the small or large
26
Whar are the sizes of the Focal spot?
Small is 1/20th the size of the 1cm filament at 0.5 - 0.6mm wide and mm in size the large focal spot is 1.0 - 1.2mm
27
What size focal spot would some specialized tube have?
As small as 0.1 mm
28
What is the grid controlled tube?
A grid-controlled tube utilizes oblique repulsion from a negatively charged mesh in front of the filaments to prevent the electrons from escaping provided they are embedded deeply into the pits of the focusing cup.
29
By switching the charge on and off ______exposures may be created.
Very short
30
What is the anode made of?
Anode is made of molybdenum
31
And what else the anode is made of?
Molybdenum usually a graphite making it light along with tungsten-rhenium alloy focal tract
32
What is the anode disc attached to?
the anode disc is attached to a molybdenum shaft (stem) ending in a copper cylinder where it reduces heat damage to the ball bearings allowing for fast rotation.
33
What are the atomic numbers of Tungstun and Rhenium?
Tungsten #74 Rhenium #75
34
Tungsten and Rhenium are high atomic numbers to catch what?
To catch electrons
35
What does tungstun and rhenium protein rich nuclei does?
So protons are positive so Additionally their proton rich nuclei create great possibility for electron interactions and help pull electrons toward the anode from the cathode.
36
How does the anode reduces heat?
In an effort to reduce heat, the average anode rotates 3400 revolutions per minute (RPM)
37
The average anode rotates how much RPM ?
3400 revolutions per minute (RPM)
38
What about the tubes used in CT? How much RPM does it rotate or run at?
Some special tubes such as those used in CT run at 10,000 RPM
39
Moving the anode what happens to the focal spot?
Moving the anode allows the focal spot to change
40
Prior to actual exposure,
the rotor starts the rotation of the anode requiring a few extra seconds.
41
What is the focal spot?
The area on the anode target that the electron beam strikes to produce x rays
42
A smaller focal spot should be utilized when possible because it?
will provide higher spatial resolution yet because it is smaller due to a more focused beam of electrons
43
The smaller Focal spot will
It will also get hotter thus mA (ctrl of filament current) is limited. The advertised fs is known as the nominal focal spot.
44
Smaller the focal spot
Better the quality of the image
45
What is the line focus principle?
The angle of the anode creates an effective focal spot projected downward thru the patient to the image receptor which is smaller than the area that is actually stricken by the electrons.
46
the glass envelope is thinner at the ________ that area through which the effective focal spot is directed
Window
47
The x-ray tube envelope is composed of a heat resistant material called?
Pyrex glass
48
The cathode and anode are surrounded by?
a glass (known as Pyrex) envelope
49
The glass envelope has a?
that has all air removed creating a vacuum.
50
Adding the vacuum was a ________ development
was a LATER development historically.
51
Why is the air molecules removed?
Air molecules would disrupt the electrons and could lead to tube failure
52
WHAT IS TUBE ARCING ? AND Even with a vacuum, as the target is bombarded with electrons WHAT HAPPENS?
tungsten gas vaporizes and accumulates along the bottom of the tube that may cause electricity to arc down and crack the glass. THIS IS KNOWN AS TUBE ARCHING
53
What is the most common cause of tube failure?
Tube Arcing
54
What is less likely to happen with METAL enclosed tube?
Electrical arcing is less likely to occur with metal enclosed tube
55
What else could damage the tube?
Damage to the tube may also occur from heat conducted down the rotor shaft to the ball bearings causing them to warp.
56
What can be reduced after ball bearings warp?
This can cause focal spot wobbling resulting in a reduction of spatial resolution & anode pitting.
57
Like a light bulb, the filament as it loses tungsten over time
will eventually burn out and snap.
58
What is the Molybdenum, Tungustun and rhenium melting point ?
Z#42 Molybdeum- MP #2617 Z#74 Tungsten-MP# 3410 Z#75 Rhenium MP#-3180
59
What is heat measured in? What is heat the product of?
Heat in measured in units known as heat units. And is the product of kVp (the potential difference)
60
Formula of the mA (tube current) and exposure time =
HU = kVp X mA X s
61
When using a three-phase generator also known as a high frequency generator how much time stronger is it?
Three phase & High-frequency are about 1.4 times stronger and generate more heat. The formula is adjusted to HU = 1.4 x kVp x mA x s ( if time was given in minutes convert to seconds always )
62
How can tube life be extended?
Tube life can be extended by performing a tube warm-up procedure when the tube has not be utilize
63
if the tube was not used all night, how would we need ?
Typically 3 exposures about 5 seconds apart using 200 mA, 1 second, and about 70 kVp.
64
Which of the following is an appropriate warm-up technique for an x-ray tube, to be repeated three times?
200 mA at 1 second and 70 kVp, at 5 second intervals
65

RAD 1126 and RAD 1125 (6 decks)

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