Electromagnetic spectrum and radioactivity

Question 1

How is EMR produced

Answer 1

1. sudden deceleration of electrons - releasing EMR decreases kinetic energy
2. The transition of electrons between shells - releasing EMR will make the atom stable again
3. interaction of electrons within the nucleus
4. radioactive decay

Question 2

what are the 6 properties of EMR waves

Answer 2

1.All transverse waves (a wave that oscillates perpendicular to wave direction, transport light and heat)
2.All travel within a vacuum at a velocity equal to the speed of light
3.All have a wavelength.
4.All have frequency.
5.Are fundamentally energy transmitted via electric and magnetic fields?
6.Dual nature – both wave and particulate energy.

Question 3

Define amplitude.

Answer 3

Maximum electric/magnetic field strength at one point, the higher the amplitude implies that the wave has higher energy.

(This is important as in TR the higher the amplitude the further the wave will penetrate through the patient)

Question 4

Define wavelength

Answer 4

horizontal difference between two consecutive peaks and troughs, shorter wavelength = higher frequency

Question 5

Define the principle of duality and consider why EMR does not adhere to wave theory.

Answer 5

The principle of duality is the idea that EMR demonstrates both the characteristics of particles and waves.

• EMR consists of a stream (wave) of discrete packages of energy (quanta) called photons. The photons carry particles of energy and thus must have a mass. Photons have no mass but are just pure energy.

Therefore EMR can be considered a stream (c characteristic of waves) of photons (characteristics of particles) with specific energy and wavelength.

Question 6

Define Planck’s law

Answer 6

the idea that all energy is emitted in quanta (discrete energy packages) supports the idea that light can be both particles and waves

Question 7

What are the 7 types of EMR

Answer 7

radio waves
microwaves
infra-red
light
Ultra violet
x-ray
gamma

Question 8

Define ionising radiation

Answer 8

very energetic radiation which has a short wavelength and high frequency. The able to remove an electron from an atom to create an ion.

Question 9

Define radioactivity

Answer 9

the natural and spontaneous process where unstable atoms emit excess energy in the form of waves and particles to become stable.

Question 10

Define nuclear instability and how/when does it happen?

Answer 10

Nuclear instability occurs when the number of atomic number increases more than neutrons. If the atomic number is greater than 84 no number of neutrons will guarantee atomic stability.

Question 11

define radioactive decay

Answer 11

when the ratio between protons and neutrons becomes unstable and energy is emitted in particles and waves (gamma rays)

Question 12

Describe the charge of:

1. alpha particles -
2. beta particles -
3. gamma rays -

Answer 12

1. alpha particles - ve+
2. beta particles - ve - or Ve+
3. gamma rays - no charge

Question 13

Describe the energy of:
1. alpha particles -
2. beta particles -
3. gamma rays -

Answer 13

1. alpha particles - high
2. beta particles - high
3. gamma rays - highest

Question 14

describe the ionising capabilities of:
1. alpha particles -
2. beta particles -
3. gamma rays -

Answer 14

1. alpha particles - very
2. beta particles - less than alpha
3. gamma rays - less than alpha and beat

Question 15

Describe the distance/penetration range
1. alpha particles -
2. beta particles -
3. gamma rays -

Answer 15

1. alpha particles - short af
2. beta particles - greater than alpha
3. gamma rays - Greater than alpha and beta

Question 16

What type of particle/wave is perfect for brachytherapy and why

Answer 16

alpha particles as they are highly ionising but cannot penetrate further

Question 17

What is a limitation of the old linear accelerator Cobalt 60

Answer 17

Cobalt 60 admitted gamma rays from a hatch in the ceiling. The problem was the gamma rays would decay due to half life and dosimetry would need to be calculated often.

Question 18

define the three types of half life

Answer 18

1.Physical half-life: the time taken for the radionuclide to decay to half its original activity (radium – 1620 years)

2.Biological half-life: the time taken for half of the activity to be removed from the body & is dependent on:
a.The type of radionuclide
b.The physiological functioning of the body particularly the target organ.

3.Effective half-life: calculated from the combined effects of the physical and biological half-lives.
a.Very important when calculating radiation dose received by patient.

Question 19

Becquerels (Bq) is used to measure

Answer 19

radioactivity

Question 20

Grays is used to measure

Answer 20

the radioactive dose deposited in tissues.