4.1 Physics Relevant to Radiotherapy

Question 1

What is the structure of an atom?

Answer 1

Atoms are made up of neutrons, protons and electrons

Each atom has a particular number of protons and neutrons held together by the ‘strong nuclear force’

Atomic number = number of protons in the nucleus

Atomic mass = number of protons + number of neutrons

Question 2

What are nucleotides?

Answer 2

Nucleotides are atoms of the same element with varying numbers of neutrons.

This is important in undersyanding radionuclides because the relative number of protons to neutrons determines how stable the nucleus is

Question 3

What is electromagnetism?

Answer 3

Describes the force of a magnetic field on a moving charged particle.

Describes how moving charged particles create a magnetic field.

Question 4

What is electromagnetic radiation?

Answer 4

Electromagnetic radiation is a form of energy transfer through space as a combination of electrical and magnetic fields.

A moving electrical field generates a varying magnetic field and vice versa.

Combined these moving fields form the electromagnetic wave.

Sometimes these behave as waves but sometimes as particles - ‘wave-particle duality’.

Question 5

How do we know that electromagnetic radiation can behave as a wave?

Answer 5

Can be reflected, refracted and interfered.

Velocity of 3x10^8 in a vacume

Question 6

What are waves?

Answer 6

Series of peaks and troughs with definable features of wavelength and amplitude.

Question 7

What is Wavelength?

Answer 7

Distance between two successive crests or troughs.
λ = lambda, measured in mete

Question 8

What is Frequency?

Answer 8

Number of waves passing a point in a unit of time
ν = nu
Number per second or Hz

Question 9

What is Amplitude?

Answer 9

The energy of a wave

Question 10

How do we know that electromagnetic radiation can behave as a particle?

Answer 10

The particles are discrete packets of energy called photons
The energy of the photons is proportional to the frewuency of the wave
E = h x v (h = Planck’s constant)
V = frequnecy = velocity/wavelength

Question 11

How is wavelength proportional to photon energy?

Answer 11

A short wavelength = higher energy photon
A long wavelength = lower energy photon

Question 12

What is the electromagnetic spectrum?

Answer 12

The electromagnetic spectrum is the range of frequencies (number of waves passing a point in a unit of time) aka the energy