Basic Physics Concepts

Question 1

What is the basic unit of energy?

Answer 1

Joule [J]

electron-volt is also commonly used in radiology

Question 2

What is the basic unit of electric charge?

Answer 2

coulomb [C]

Question 3

What is the basic unit of power?

Answer 3

watt [W]

Question 4

what is the basic unit of absorbed dose of ionizing radiation?

Answer 4

Gray (Gy)

j/kg

Question 5

What is a Gray [Gr]?

Answer 5

The basic unit of absorbed dose of ionizing radiation

Question 6

What is a sievert?

Answer 6

A unit for the ‘health effect of ionizing radiation on the human body’.

Question 7

Are x-rays higher or lower frequency than visible light?

Answer 7

higher

Question 8

In electromagnetic radiation, how are the directions of these fields related to each other:

• magnetic field
• electric field
• the direction of propagation/ movement?

Answer 8

They are all at 90 degrees to each other

Question 9

What is an electron-volt [eV]

Answer 9

The quantity of (kinetic) energy an electron would have if accelerated over 1V.

Equivalent to 1.6 x10^19 J

Question 10

What is the difference between Gamma rays and X-rays?

Answer 10

Gamma rays are produced in the nucleus by nuclear de-excitation

X-Rays are produced in the atomic shell by atomic de-excitation

Question 11

When talking about the characteristic of different elements/ atoms, what do the letters ‘Z’ and ‘A’ normally refer to?

Answer 11

Z = atomic number = number of protons
A = mass number = number of protons + number of neutrons

Question 12

Which electron shell is on the inside of an atom?

Answer 12

the k shell

Question 13

In X-ray production:

Is the cathode or anode the filament or target?

Answer 13

Cathode = filament
Anode = target

Question 14

What are typical voltage difference between the filament and the target in x-ray production?

Answer 14

50-150kV

Question 15

What are the two types of radiation produced in x-rays?

Answer 15

Continuous radiation (Bremsstrahlung radiation)
Characteristic radiation

Question 16

What is Continuous radiation also known as?

Answer 16

Bremsstrahlung radiation?

Question 17

What does Bremsstrahlung radiation mean in german?

Answer 17

Braking radiation

Question 18

What occurs to create Bremsstrahlung radiation?

Answer 18

an electron swerves around the nucleus and loses some speed,
the energy lost by this swerve is released as a photon/ x-ray

Question 19

Why is Bremsstrahlung radiation called ‘Continuous Radiation’

Answer 19

The energy of x-rays produced can be anywhere from 0 to whatever the maximum keV of the electrons was.

This gives a continuous spectrum of radiation (although it’s not all in equal amounts.

Question 20

How does characteristic x-ray radiation occur?

Answer 20

Produced when an electron is knocked out of a shell and then another electron falls down into that shell, releasing it’s extra energy when doing so in the form of an x-ray

Question 21

Why is characteristic x-ray radiation, characteristic?

Answer 21

X-ray photons have unique (discrete) energy values which are characteristic of the target atom

Depends on the difference in binding energy between the different electron shells

Question 22

Does increasing kVp affect beam quality or quantity?

Answer 22

Both

Question 23

What is Half Value Layer?

Answer 23

The thickness required to reduce beam intensity by 50%

Question 24

Does the anode material affect the beam quality of quantity?

Answer 24

Both

Question 25

How does the conversion efficiency of energy into continuous spectrum x-rays change with an increasing atomic number of the anode material?

Answer 25

The conversion efficiency increases as the atomic number increases.

The intensity of x-rays is approximately proportional to the atomic number.

Question 26

What stops electrons from diverging as they travel from the cathode to the anode in x-ray production?

Answer 26

The focusing cup

Question 27

What is the electrical potential of a focusing cup?

Answer 27

the same negative potential as the filament

Question 28

How do x-ray machines avoid overheating of the anode?

Answer 28

A rotating anode,
so that no one physical spot has too much of the current flow through it.

Further enlarging the area hit by having it at an angle

Also cooling oil etc

Question 29

What is a focal spot in x-ray generation?

Answer 29

The point where x-rays are emitted from?

Question 30

What is the Line-Focus Principle in x-ray generation?

Answer 30

The size of the effective focal spot can be smaller than the size of the actual focal spot if the anode is at a sharp angle.

Question 31

What is the ‘Anode Heel Effect’

Answer 31

If the anode where x-rays are produced is at an angle then there will be an uneven distribution of x-rays.

The x-rays are usually not produced at the surface of the anode, and so some will have to travel through more metal to get out of the anode.

Question 32

Due to the ‘Anode Heel Effect’, are x-rays usually more pronounced on the anode or cathode side of x-ray films?

Answer 32

Cathode side,

Less intense towards the anode side

Question 33

What is collimation of x-rays?

Answer 33

The x-ray field is limited by heavily shielded windows.

Question 34

What is the unit of measurement used for heating of x-ray machines?

Answer 34

Heat Units

unit of potential x unit of tube current x unit of time

Question 35

What are common causes of x-ray tube failure?

Answer 35

loss of vacuum
cathode filament failure
anode damage
bearing failure