X-ray Production (Ch 8)

What type of wave are x-rays?

Electromagnetic

All electromagnetic waves have what four characteristics in common?

1. They are in the form of a sine wave

2. They act like a wave and like a particle (“wave-particle duality”)

3. They all travel at the same speed, the speed of light (3 ×10^8 meters per second)

4. They can travel through a vacuum, whereas other waves need a medium such as air, water, etc)

As the wavelength of x-rays increases, the frequency ______

Decreases

As the wavelength of x-rays decreases, the frequency ______

Increases

What are the four major components of an x-ray tube?

1. Glass tube or glass envelope

2. Hot filament or cathode assembly

3. Target or anode assembly

4. Potential difference

The glass tube or envelope prevents the collision of?

Electrons with air molecules

The glass tube or envelope increases the life of the tube by preventing?

Oxidation (rusting) of the filament

Is the cathode assembly negatively or positively charged?

Negatively charged

The hot filament or cathode assembly produces what?

Themions (incident electrons)

Is the target or anode assembly negatively or positively charged?

Positively charged

What happens at the target or anode assembly?

It’s where thermions interact with the target material to produce x-rays

What is the potential difference produced by?

The tube circuit

What does the potential difference cause to happen?

The thermions to jump the gap at very high speeds

During x-ray production, electrical potential difference changes to kinetic energy when kVp is applied to the ______ and it crosses the gap

Thermionic cloud

What are the two circuits that are located in the x-ray machine?

1. Filament or low voltage circuit

2. Tube or high voltage circuit

The low voltage circuit ______ the filament

Heats up

The high voltage circuit provides the _______

Potential difference

What are the two general conditions needed to produce x-rays?

1. A high speed electron that undergoes rapid deceleration

2. An outer shell electron that drops into an inner shell of an electron

What is a high speed electron also known as?

Incident electron

When a high speed electron undergoes rapid deceleration, the electron’s ______ is lost, some in the form of an x-ray

Kinetic energy

When the outer shell electron drops into an inner shell of an electron, the electron goes from a higher energy state to a lower energy state, so the energy is released in the form of?

An x-ray

The energy of the x-ray is determined by the _______ of the electron released

Binding energy

To accomplish x-ray production within the x-ray tube, specifically four things must happen:

1. There must be a source of electrons from the filament wire, including the process of thermionic emission

2. The electrons must be focused into a tight beam by a device called a focusing cup

3. There must be a high potential difference (voltage/kVp) between the cathode and anode

4. The high speed (incident) electrons must be stopped as they interact with the target or focal track of the anode

Electrons being boiled off the filament is called?

Thermionic emission

The electrons that are boiled off the filament are accelerated how fast from cathode to anode?

½ the speed of light

Over ____% of the electron’s kinetic energy is converted into heat

99

Less than ___% of electrons kinetic energy is converted into x-rays

1

At the anode, two processes can occur to create diagnostic x-rays:

1. Bremsstrahlung interactions

2. Characteristic interactions

What does “bremsstrahlung” mean in German?

Braking radiation

Brems interactions occur when the negatively charged electron interacts with the _________ of a tungsten atom in the target

Positively charged nucleus

During a brems interaction, when the electron comes close to the nucleus, it slows down, losing some or all of its _________

Kinetic energy

During a brems interaction, the amount of kinetic energy an electron loses is determined by how close the electron comes to the _______

Nucleus

During a brems interaction at the anode, the kinetic energy the electron loses is converted into an?

X-ray photon

During a brems interaction, the energy of the x-ray photons is equal to the difference between?

The entering and exiting kinetic energy of the electron

Brems x-rays are heterogenous and _________

Polyenergetic

Brems x-rays are ________ in energy and wavelength

Non-uniform

A _____ electron can cause numerous brems interactions

Single

When will a characteristic interaction occur?

When the incident electron interacts with an inner shell electron of the tungsten target atom

With characteristic interactions, as long as the electron has more ______ energy than the ______ energy of the orbital electron, it will eject the orbital electron from its shell

Kinetic, binding

With characteristic interactions, the atom will be ______

Ionized

During characteristic interactions, an electron from an outer shell will drop into the hole while another electron will drop into the newly created hole, this being know as?

“Cascade effect”

The energy that is released during characteristic interactions, is in the form of?

An x-ray

The k-shell of a tungsten atom has a binding energy of?

69.5 keV

The l-shell of a tungsten atom has a binding energy of?

12.1 keV

The m-shell has a binding energy of?

2.8 keV

The k-shell binding energy of molybdenum is?

20 keV

Between 80 and 100 kVp, _____% of the x-rays produced are bremsstrahlung

80-90

Between 80 and 100 kVp, _____% of the x-rays produced are characteristic

10-20

Below 70 kVp, _____ x-rays produced are bremsstrahlung

100%

Below 70 kVp, ______ x-rays produced are characteristic

0%

Why is tungsten the target material?

1. High atomic number, which produces useful characteristic radiation of 69.5 keV

2. High melting point

What is tungstens atomic number?

74

What is the melting point of tungsten?

3370 degrees C

What is the melting point of thoriated tungsten?

3420 degrees C

The efficiency of the x-ray tube can be determined by using what equation?

Efficiency (E) = K x Z x kVp

What does K= in the efficiency equation?

1 × 10^-4

What does Z= in the efficiency equation?

Atomic number of the target material

The three principles electrical quantities that can be adjusted by the radiographer is?

1. kVp

2. mA

3. Time

Each electron has ____ keV of energy

1

The electrons interact with individual atoms of the anode material; the two types of interactions that produce radiation are:

1. An interaction with electron shells produces characteristic x-ray photons

2. An interaction with the atomic nucleus produces bremsstrahlung x-ray photons