Xray Physics

Question 1

Define electromagnetic radiation

Answer 1

A form of energy that propagates as both electrical and magnetic waves in the form of photons

Question 2

How does EMR work

Answer 2

Energy transported through space via a combination of varying electric (E) and magnetic (H) fields which are 90’ to the direction of propagation and to each other (aka transverse radiation)

EMR exhibits wave-particle duality where visible light tends to act like a wave and x-rays and gamma rays act like particles (photons)

Question 3

Difference between the production of x-rays and gamma rays

Answer 3

X-ray production due to atomic de-excitation (electrons)

Gamma ray production due to nuclear de-excitation (nucleus)

Question 4

Briefly explain the x-ray tube

Answer 4

Filament cathode gets heated by applying voltage to release and accelerate electrons (thermionic emission),
Emitted towards tungsten target on anode, where e rapidly lose energy by interacting with atoms

Target emits radiation towards lead collimators which defines x-ray beam size.

Anode and cathode within a glass wall, vacuum
Surrounded by lead-liked wall with cooking oil within

Question 5

Explain Bremsstrahlung radiation and how it relates to x-ray production

Answer 5

Photon released when an electron is decelerated by the electric field of an atomic nucleus and loses kinetic energy (ie releases energy as a photon), more energy released as they approach closer to the nucleus (tighter bend = more braking = more energy lost)

Question 6

Define characteristics radiation

Answer 6

X-ray radiation emitted when an atom undergoes a transition between energy levels in its electron structure.

Characteristic refers to the fact that the emitted radiation has discrete energy values that are unique to each element

Question 7

Explain c=νλ

Answer 7

C = speed of light (3x10^8ms-1)
ν = frequency of EMR
λ = wavelength

Question 8

Photon energy equation

Answer 8

E=hν or E=hc/λ
Where h = 6.626x10^-34 Js (Planck’s constant)
Typical x-ray photon λ = 10^-11m
1eV = 1.6x10^-19J

Hence typical x-ray photon
E = 2x10^-14 = 1.2x10^5eV = 120keV

Question 9

What is the probability of occurrence of a photoelectric effect?

Answer 9

PE α Z^3/E^3
Where Z = atomic number, E= incident photon energy