Radioactivity Principles

Question 1

What are the highest value you can have for protons and neutrons in a stable nuclei?

Answer 1

No more than 83 protons or 126 neutrons

Increased protons + increased neutrons = stability maintained

Question 2

Why does adding more neutron to an increase in protons maintain stability?

Answer 2

The repulsive forces can be exerted over a greater area than the
forces of attraction

On a graph the line of nuclei stability diverges from P=N line

Question 3

Definition: Radioactivity

Answer 3

The process whereby some nuclides undergo spontaneous changes in the structure of their nuclei resulting in particle and radiation emission.

The nucleus rearranges itself to try and gain stability
Each time nucleus re-arranges itself this is a disintegration

Question 4

Definition: Radionuclide

Answer 4

An unstable nuclide which is radioactive.

Radioactivity is the way a radionuclide becomes stable
Nuclides are always trying to attain the ground state (lowest
possible energy state)
For some even at this level they are still unstable

Question 5

Definition: Nuclide

Answer 5

An atom of an element with a specific Z (Atomic number) and A ( atomic mass) and they can be grouped
together.

Question 6

Definitions: Isotopes

Answer 6

Isotopes are nuclides with the same number of
protons

Focus on IsotoPes to help you remember

Question 7

Definition: Isobars

Answer 7

Atoms of different elements with the same number of nucleons/atomic mass

Focus on IsobArs to help you remember

Question 8

What may disintegration result in?

Disintegration = energy released when unstable atomic nucleus undergoes radioactive decay

Answer 8

• Change in atomic Mass number
  – Change in Atomic number
  – Change in both

Question 9

Laws of Energy Conservation =

Answer 9

Energy cannot be created or destroyed - it can only be transferred from one type to another

Question 10

What is the SI unit for decay?

Answer 10

Becquerel (Bq)

1 Bq=1 radioactive decay per seond

Question 11

What alternative units do we use in practice for decay?

Answer 11

MBq (megabecquerel)
or
GBq (gigabecquerel)

Question 12

3 types of decay emissions

Answer 12

• Alpha particle emission
• Isobaric Transitions : Beta-/Beta+/K capture
• Isomeric Transitions: Gamma Rays

Question 13

What is formed after disintegration?

Answer 13

Daughter Nuclide

This may or may not be stable

Question 14

What transformations make a radionuclide stable?

Answer 14

Decay Scheme

Question 15

What happens during Alpha Particle Emission?

What is the particle made of & what is identicle in structure to?

Answer 15

Radionuclide emits a heavy charged particle - Alpha Paticle

2 protons & 2 neutrons
Helium Nuclei

Question 16

Why does Alpha Particle Emission happen?

How?

Answer 16

To achieve a more stable state for an unstable nucleus.

Drops the stomic mass number by 4
Drops the atomic number by 2

Question 17

Name 6 properties of Alpha Particle?

Answer 17

• Positively Charged (+2)
• Relatively heavy
• Causes ionisation
• Relatively slow-moving – Lose their energy quickly
• Short range
• Easily stopped

Question 18

What solves an imbalance in protons and neutrons?

Answer 18

Isobaric Transition(beta decay)

The process of electron transfer - atomic number changes as proton is changed into a neutron

Question 19

Isobaric Transitions

Why may a neutron be converted into a proton or vice versa?

Answer 19

If excess energy is less than the binding energy of the nucleons

This increases or decreases atomic number by 1
Number of nucleons remains the same

Question 20

Isobaric Transitions

What are the 3 types?

Answer 20

-Beta minus (negatron) – too many neutrons (turn into a
proton) atomic no (Z) will increase
-Beta plus (positron) – too many protons(turn into a
neutron) atomic number (Z) will decrease
-Electron Capture – lots of protons draw in electron (K
shell)

Overall mass stays the same
Associated with the production of neutrinos

Question 21

When does Beta minus Particle Emission happen?

What occurs during BMPE?

Answer 21

When too many neutrons are in the nucleus

Neutron turns into a proton
B- particle and an antineutrino simultaneously
produced
Atomic number increases

Question 22

What occurs during Beta+ or Positron Decay?

Answer 22

proton turns into a neutron, emitting a positron
and a neutrino

reverse of beta- decay

Positron is effectively a positively charged electron

Question 23

Positron Decay

What happens?

What is an example of an isotope which undergoes positron decay?

Answer 23

• When all KE is lost, it combines with a resting electron
• “Annihilation radiation”

18F

Question 24

Beta Particles Properties

What does a Beta Particle resemble?

What can they cause?

Answer 24

-Emitted with very high KE
-Cause less ionisation than alpha particles
-Greater range than alpha particles
-Stopped easily (thin sheet of aluminium)

Electron

Localised damage to body tissues

Question 25

# Isomeric Transition - Gamma Decay What does isomeric mean?

Answer 25

There is no change in the Atomic or Mass number

Question 26

# Isomeric Transition - Gamma Decay Alpha or Beta decay leaves daughter nucleus in an excited state with excess energy - how does it change to a stable state?

Answer 26

Excess energy is emitted as a Gamma Ray or passed to the orbital electrons

Question 27

Gamma Ray Properties

Answer 27

* No mass * No charge * Ionising (indirect ionisation) * Interact like X-rays (but differentiate between γ and X-rays) * Very penetrating

Question 28

Order the Penetraing Distances of the below radiation: Gamma & X-rays, Alpha, Beta

Answer 28

Alpha Beta Gamma & X-rays

Question 29

Exponential Laws

Answer 29

provide a set of guidelines for simplifying calculations and expressions involving exponents.

Question 30

Exponential Decay Equation symbol meanings: A = A0.e-λt

Answer 30

A = The activity after time (t) A0 = Initial activity of the sample λ = Decay constant for radionuclide e = Exponential constant

Question 31

What is the Half-life of a radionuclide?

Answer 31

Each radionuclide has its own decay rate which can be seen by its decay constant, or by noting the time it takes for its activity to reduce by 50%

Question 32

What part of radiotherapy uses gamma emissions?

Answer 32

Brachytherapy ## Footnote Reminder: a type of internal radiation therapy where a radioactive source is placed inside or close to a tumor to deliver radiation directly to it.

Question 33

What scan uses positron emissions?

Answer 33

PET scanning

Question 34

Brachytherapy - Optimum Gamma Ray Energy: High vs Low | each purpose

Answer 34

– HIGH improves dose uniformity – LOW reduces radiation protection requirements

Question 35

Brachytherapy - Half life Very long vs Short | Which type of implants is each good for?

Answer 35

– Very long: good for temporary implants – Short: good for permanent implants ## Footnote Half life is long enough so that decay during treatment is negligible (not considered important or impactful)