Basic Physics

Question 1

What is beam intensity?

Answer 1

total amount of energy per unit area travelling per unit time

Question 2

Does all electromagnetic radiation travel at speed of light in vacuum?

Answer 2

Yes

Question 3

What are secondary electrons?

Answer 3

Are electrons produced during compton

Their range depends on density of material and initial energy

**The more energy the photoelectron receives the higher the scatter angle of the photon**

Recoil electrons in compton

• Can only go forwards or sideways

Photons can be scattered in any direction

• can be alpha or beta particles
• ionising

Question 4

How may types of radiation can radionuclides emit?

Answer 4

Alpha

Beta

Gamma

Question 5

What is atomic number of tungsten?

What is its K edge ?

Answer 5

Atomic number = 74

K edge 70

Question 6

What is atomic number of lead?

Answer 6

Atomic number = 82

K edge = 88

Question 7

What is atomic number of iodine?

What is K edge?

Answer 7

Atomic = 53

K edge = 33

Question 8

What is atomic number and K edge of barium?

Answer 8

Atomic = 56

K edge = 37

Question 9

What is the mean energy of the x-ray beam relative to the operating kV?

Answer 9

Mean energy is approx 50% of operating kV

The operating kV is the max energy possible

Question 11

What does K alpha radiation result from?

Answer 11

Electron falling from L to K shell

Question 12

What does K beta radiation result from?

Answer 12

Electron falling from M to K shell

Question 13

What effect does increasing tube current have on x rays and curve?

Answer 13

Increasing mA (tube current) increases NUMBER of electrons hitting anode and therefore number of x- rays

Double tube current = double amount of x rays

Increasing mA does not affect curve shape, just makes it go upwards increasing amplitude

Question 14

How does increasing kV affect curve shape?

Known as Tube Potential

Potential = kV

Answer 14

Curve up and to the right

Increases:

• number of x-rays
• energy of electrons

Question 15

What is tube output equal to?

Answer 15

= kV²

Question 16

What qualities does tube filament have?

Answer 16

High melting point

High resistance

Low vapour pressure

Question 17

Probability of photoelectric reaction?

Answer 17

• Proportional to the Atomic number³
• Inversely proportional to the kV³ (ie low energy event)
  • 1 / kV³

Question 18

IsoBARS have same…

Answer 18

Mass number

different atomic number

Question 19

Alpha Particles

What happens in decay?

Answer 19

Mass number decreases by 4

Atomic number decreases by 2

• High energy and very damaging
• Particles carry a charge of +2
• Travel 0.1cm in TISSUES
• Have energy of 4-7MeV

Question 20

What is included in electromagnetic spectrum?

Answer 20

• Gamma
• X ray
• UV
• Visible light
• Infrared
• Microwave
• Radio

X-rays produced by electron reactions

Gamma rays produced by nucleur reactions

• Both cannot be distinguished by frequency and wavelength

Question 21

What voltage passes through tube?

Answer 21

10V

10A

Question 22

What dictates chemical properties of element?

Answer 22

Electrons in outermost shell are responsible for chemical properties

Question 23

What is 1 MBq equal to?

Answer 23

1 million decays per second

Question 24

Inverse Square Law

Answer 24

Doubling of will reduce intensity by 1/4

The inverse square law states that the intensity of radiation emitted from a point source will reduce in intensity, proportional to the square of the distance from that point

Question 25

How it HVL calculated?

Answer 25

0.69/LAC

Question 26

Does electromagnetic radiation have a mass?

Answer 26

NO All electromagnetic radiation travels at the speed of light in a vacuum

Question 27

What is definition of HVL?

Answer 27

The thickness of a material required to reduce the **INTENSITY** of a beam by half HVL increases as a beam pass through materials

Question 28

Does increased kV result in less side scatter?

Answer 28

Yes Therefore reduced kV results in more side scatter

Question 29

What is intensity equal to?

Answer 29

The total **ENERGY** per unit time and area Increased filter thickness will reduce intensity

Question 30

What propoerties do isomers have?

Answer 30

Same atomic and mass numbers **Different half lives as they are metastable**

Question 31

What effect predominates in low atomic number materials?

Answer 31

Compton * Air * Soft tissue * Water

Question 32

What effect predominates in higher atomic number materials?

Answer 32

Photoelectric * Bone * Contrast

Question 33

What is Crurie equal to?

Answer 33

3.7x10¹⁰ transformations per second A bequerel is 1 transformation per second Decay constant is **inversley proportional** to half life

Question 34

How is absorbed dose measured in Radiography?

Answer 34

Ionisation chambers

Question 35

How is radiation dose read out on electronic dosimeters?

Answer 35

Silicon diodes

Question 36

Film Badges

Answer 36

Calibrated with caesium source Have open window for detection of beta particles

Question 37

What is atomic number equal to?

Answer 37

Just the number of **Protons**

Question 38

What is K edge of calcium?

Answer 38

K edge = **4** Most natural elements in the body have a low K edge

Question 39

What is speed of light?

Answer 39

3x10⁸

Question 40

What is Mass attenuation coefficient unit?

Answer 40

**m^2/kg** **cm²/g**

Question 41

What is mean beam energy?

Answer 41

50% of the operating tube kV

Question 42

What is max photon energy equal to?

Answer 42

The operating kV

Question 43

What is the decay constant?

Answer 43

The fracttion of nuclei decaying per unit time

Question 44

What is accelerating voltage in x-ray tube?

Answer 44

60 - 120kV

Question 45

What determines physical properties of an atom?

Answer 45

Mass number

Question 46

Can protons with sufficient energy be forced into a nucleus?

Answer 46

Yes As seen in cyclotron

Question 47

What is linear attenuation coefficient?

Answer 47

The fraction of attenuated incident photons in a monoenergic beam per unit thickness of material Depdendent on density Units are **cm^{-1 or} mm^-1**

Question 48

Does a change in kV or mA affect characteristic energy peaks?

Answer 48

NO Doesnt affect distribution of peaks or energy but does result in **more characteristic radiation**

Question 49

What happens in bremmstraglung?

Answer 49

Filament electrons penetrate K shell but get deflected by nucleus Continuous spectrum graph only represents Bremmstrahlung

Question 50

What increases probability of compton?

Answer 50

High electron density High physical density

Question 51

Does increasing the kV affect number of filament electrons produced?

Answer 51

NO Just increases total amount of x-rays produced at the target