X-ray Production, Spectrum, and Interaction in Radiology

The KE of the incident electron is an x-ray tube is

about 1% efficient in the production of XRs

The shift of the characteristic XR spectrum to higher energy occurs because of which of the following

an increase in target atomic number

Useful characteristic XRs are produced in tungsten

by removal of a K-shell electron

A L-shell electron (binding energy = 26 keV) is removed from an atom that has M-shell binding energy of 4 keV and N-shell binding energy of 1 keV. If a free electron fills the vacancy in the L-shell, the characteristic x-ray photon produced will have an energy of:

26 keV

What is produced when the incident electron excites an outer-shell electron

thermal energy

The energy of characteristic x-rays increases with increasing

atomic number of the anode target

XRs are produced when

incident electrons interact with anode target atoms

Characteristic XRs

are characteristic of target Z#

When a tungsten-targeted XR tube is operated at 68 kVp

some incident electrons may have 68 keV

Gold is sometimes used as target material in special types of radiation-producing systems. Its electron-binding energies are as follows: K-shell 81 keV; L-shell 14 keV; M-shell 3 keV; and N-shell 1 keV. Which of the following characteristic x-rays would be produced with operation at 90 kVp?

67 keV

In a tungsten-targeted XR tube operated at 90 kVp, the most abundant x-ray would be a

30 keV bremsstrahlung x-ray

Which of the following electron transitions results in the most useful bremsstrahlung x-ray

none; brems has nothing to do with electron transitions

Bremsstrahlung radiation is produced by

the conversion of incident electron KE to electromagnetic energy

Bremsstrahlung x-rays produced in a tungsten-targeted XR tube

outnumber characteristic x-rays

Which of the following incident electron-target interactions results in XR emission

removal of an inner-shell electron

When mAs is increased, XR quantity

increases proportionally

When XR tube filtration is increased, XR quantity

decreases

In general, XR quantity will increase with an

increase in kVp

Another meaning of "x-ray quantity" is x-ray

intensity

Which of the following does not affect x-ray quantity

radioactivity

When filtration is added to an XR tube, which of the following increases

radiation quality

It is often stated that mAs controls quantity and kVp controls

quality

An x-ray beam can be made to have higher effective energy is which of the following occurs

filtration is added

Reducing kVp will do which of the following

soften the x-ray beam

XRs of higher maximum energy can be obtained by doing which two of the following

increasing kVp and increasing atomic number of target material

The area under the curve of the x-ray emission spectrum represents

the total number of x-rays

A general emission spectrum contains

both characteristic and bremsstrahlung x-rays

The x-ray emission spectrum represents

x-rays emitted from the tube

The amplitude of the Bremsstrahlung x-ray emission spectrum

has maximum value at energy approximately one third of the kVp

To construct an x-ray emission spectrum, one must know the

number of x-rays at each energy interval

Define photon

small bundle of massless energy; what is produced when the high-speed electrons from the cathode strike an anode target

What are photons depicted by

a wavy arrow

Define characteristic cascade

the process of outer shells filling the void of an ejected electron

Define binding energy

the energy required to remove the electron from its shell

What is binging energy measured in

electron volts (eV)

Define incident electron

the electron that causes a brems (by interacting with the nuclear force field) or characteristic (by ejecting an inner-shell [k-shell] electron) XR

What is an incident electron represented by

a solid arrow

Heterogenous beam

a beam of radiation consisting of a spectrum of photon energies (polyenergetic)

Homogeneous beam

a monoenergetic beam consisting of particles or photons with the same energy

Average energy

equal to 1/3 of the kVp; the average amount of penetrability power a photon in the XR beam can have

Maximum energy

kilovoltage peak; the max amount of penetrability power a photon in the XR beam can have

Emission spectrum

Graphical representations that measures the type of x-rays (Brems vs. Characteristic) comprising the primary beam; x axis = quality (energy); y axis = quantity (amplitude/intensity)

Quantity

Represents the total number of X-ray photons in the beam; also called intensity

Quantity is measured as Exposure in units of

c/kg or Air-Kerma in units of Gya

Quantity is controlled by

mAs (via thermionic emission)

Quality

Represents the average energy/penetrability of the XR beam

Quality is controlled by ____ and equal to ___________

kVp; 1/3 of the kVp

Quality is measured in

half-value layers

Tube potential

The difference in charge between the negative cathode and the positive anode side

Tube potential ____________ as kVp increases

increases

Tube potential is measured in units of

kilovoltage

Tube current is measured in

milliamperage

Tube current begins at the _____________ and is...

filament via thermionic emission; the number of actual electrons flowing across the tube (from filament wires on the cathode side to the anode target on the anode side)

Exposure time

the amount of time electrons are flowing through the tube and x-rays are being produced

Exposure time is measured in

seconds

What is the source of electrons within the x-ray tube?

Filament wires via thermionic emission

Where, specifically, do tube interactions occur?

Within 0.25-0.5 mm of anode target

What are the possible interactions that can occur between an incident electron and target atom?

Heat, Bremsstrahlung, and Characteristic

The type of interaction that occurs in the production of x-rays is dependent upon

kVp (above or below 70)

What percent of target interactions result in the production of x-rays?

Less than 1%

List the other names is Brems interaction is known by

Continuous radiation, polychromatic, white radiation, braking rays

With what part of the atom does the incident electron interact?

Nuclear force field

When will a bremsstrahlung photon be produced

When incident electron brakes; in the XR beam, it will make up 100% of the interactions occurring when the kVp is less than 70 and 85% when the kVp is over 70

The energy of a bremsstrahlung photon is dependent upon

kVp // energy of the incident electron and the proximity of the incident electron to the nucleus as it passes

The maximum energy of a bremsstrahlung photon is equal to

The given kVp // incident electron energy (ex. if the kVp is set to 65, then the maximum energy that the photon can have is 65 kev)

During an exposure, an incident electron strikes the anode with an energy of 100 kVp: If the electron passes very close to the nucleus, what is the approximate energy of the photon created?

High, likely near 100 kVp (~99 keV)

During an exposure, an incident electron strikes the anode with an energy of 100 kVp: If the electron passes very far from the nucleus, what is the approximate energy of the photon created?

Low energy; a lot less than 100 kVp (~1 keV)

During an exposure, an incident electron strikes the anode with an energy of 100 kVp: If the electron passes very far from the nucleus, what is the approximate energy of the electron as it exits?

It would still have somewhat of a high energy since it did not convert much energy into a photon (~99 keV)

At 60 kVp, what percent of the primary beam is made up of bremsstrahlung photons

100%

At 95 kVp, what percent of the primary beam is made up of bremsstrahlung photons

85%

Which interaction is this

Bremsstrahlung

Which interaction is this

Characteristic

What other name is characteristic interactions known by

discrete

With what part of the atom does the incident electron interact?

Inner-shell electrons (K-shell)

When is a characteristic photon produced?

during cascade effect

The energy of a characteristic photon is dependent upon

The atomic number of the target material (binding energies of the shells)

The maximum energy of a characteristic photon is equal to

the binding energy of the K-shell, usually 69.5 keV since tungsten is often the target material used; only occurs when a free electron fills the ionized K-shell

During an exposure, an incident electron with an energy of 110 keV ejects a k-shell electron from orbit. What is the maximum energy of the characteristic photon produced?

69.5 keV

The energy of characteristic photons will change when which of the following is modified? (Choose one.) kVp, mA, filtration, anode material, generator type

anode material

What are the binding energies of a tungsten atom: K-shell

69.5 keV

What are the binding energies of a tungsten atom: L-shell

12.1 keV

What are the binding energies of a tungsten atom: M-shell

2.8 keV

What are the binding energies of a tungsten atom: N-shell

0.6 keV

What are the binding energies of a tungsten atom: O-shell

0.08 keV

At 50 kVp, what percent of the primary beam is made up of characteristic photons?

0%

At 85 kVp, what percent of the primary beam is made up of characteristic photons?

15%

With what part of the atom does the incident electron interact?

Valence (outer-shell) electrons

At what point in the interaction is heat produced?

When incident electrons excite valence electrons AND return from the excited state

List two alternative names for heat

Infrared radiation and thermal energy

What percentage of tube output is heat?

99.8%

A general emission spectrum demonstrates which interactions

brem and characteristic

A discrete emission spectrum demonstrates which interactions

characteristic only

A continuous emission spectrum demonstrates which interactions

brems only

On a spectrum, bremsstrahlung radiation is represented by a

bell curve or brems hump

On a spectrum, characteristic radiation is represented by

vertical lines called characteristic peaks

An increase or decrease in amplitude represents changes to

quantity

A peak shift right or left represents changes to

quality

An increase in which factor(s) will result in an increase in amplitude?

mAs, kVp, generator efficiency, atomic number

An increase in which factor(s) will result in a peak shift to the right?

kVp, filtration, generator efficiency, and atomic number

An increase in which factor will result in a decrease in amplitude?

Filtration