introduction to radioactivity

Question 1

Atomic Structure

Answer 1

Subatomic particles
Smallest unit of electrical charge is the electron
= -1.6 x 10 -19 Coulombs (C)
Experience a force when placed in an Electromagnetic Field
Two types of electrical charge at an atomic level

Question 2

Nucleons:Protons and Neutrons

Answer 2

Proton
U+U+D
2/3 + 2/3 + (-1/3) = 3/3 = 1 Proton = Positive Charge 1
Neutron
D+D+U
(-1/3) + (-1/3) + 2/3 = 0/3 = O Neutron = No Charge / Neutral

Up Quark = 2/3 electric charge
Down Quark = -1/3 electric charge

Question 3

Strong Nuclear Force

Answer 3

What holds the nucleons together in the nucleus
Nucleons come close to each other
Results in exchange of particle called a meson
Behaves like a ping pong ball
Creates a strong nuclear force
Pulls the nucleons together
Range is 10-15m

Question 4

Two Types of Nuclear Force

Answer 4

Strong Nuclear Force
Holds the nucleus together
Works at short distance of 10-15m

Weak Nuclear Force
Responsible for Radioactive Decay

Question 5

Strong Nuclear Force (SNF)

Answer 5

What is holding the nucleons in the Nucleus?
Law of Electromagnetic force states ‘that like charges repel and opposite charges attract’
Protons are positively charged
Strong Nuclear Force works in the 10-15 m – 10-16 m range

How does it work?
Proton and Neutron are stable
Contain Quarks and Gluons
These exchange Kinetic Energy which allows energy to be exchanged between the particles.
As mass increases the SNF cannot hold all the nucleons on the nucleus leads to Radioactive Decay

Question 6

What is an ISOTOPE

Answer 6

Every element in the periodic table has multiple variations
Same atomic number (protons) but different mass
Atomic number provides the chemical identity of the element
Some Isotopes are stable whilst others are unstable

C-12 P:6 C-13 P:6 C-14 P:6
n:6 n: 7 n: 8
Stable Stable Radioactive Half life

57000 years or 5.7 x 103 years

Different Isotopes of Carbon

Question 7

Radioactive Decay

Answer 7

Also Known as:
Nuclear Decay
Radioactivity
Radioactive Disintegration
Nuclear disintegration

Question 8

What is Radioactive Decay?

Answer 8

Process by which an unstable atom loses energy
Emission of particles – radiation
Decay occurs at a constant predictable rate
Known as the HALF LIFE (t1/2) or Decay Constant (λ)
Three types of Radioactive Decay
Alpha ( )
Beta ()
Gamma ()

Question 9

The Decay Constant (λ) or Half Life (t1/2)

Answer 9

Time required for the activity of the radioisotope to reduce to half of the initial activity rate
Time taken to reduce by 50% of the initial rate
Means half of the initial quantity has become a different element

Question 10

Units of Activity

Answer 10

SI unit for radioactivity is the Becquerel (Bq)
1 Bq = 1 disintegration per second
1 Bq is described as 1 radioactive decay per second
Specific Activity = activity of the Radionuclide per unit mass
BqKg-1

Question 11

Radioactivity in Radiography

Answer 11

Radiopharmaceutical tracer
Radio-isotope is attached to a compound or chemical that cell or cells need
Inserted into the body - injection, ingested, inhaled
Radiation emitted is received and converted into a digital image

Question 12

Radio-isotope Diagnostic Radiography

Answer 12

Isotope used – Technetium 99m (Tc99m) artificially produced
Starts with stable Molybdenum (Mo98) in a generator and bombarded with neutrons
Produces an Isotope Mo99 decays every 66 hours into Technetium 99m (Tc99m or 99mTc)
Tc99m bound to a carrier compound and is used to vector to the cell of interest
Often a glucose molecule
Tc99m or 99mTc has λ of 6 hours and decays with Gamma () rays at an energy level of 140.5 KeV which is constant

Question 13

Radioisotope Iodine

Answer 13

Xenon (Xe124) is bombarded with protons to produce Iodine 123 (I123)
I123 decay rate is 13.22 hrs this achieved by emitting radiation until it reaches a steady state
I123 Decays to Tellurium 123 (Te123) half life = 9 x 1016 years so stable in our life time via a Gamma () at 159 KeV energy level
Used in the detection of Thyroid disease and cancer
Measuring the Gamma emission equates to uptake of isotope which equates to functionality of the organ
More Gamma greater emission rates greater the uptake of the organ

Question 14

Radioactive Decay – Alpha

Answer 14

Large nucleus
Consists of 2 neutrons and 2 protons to from  particle
Is a Helium particle
The element emits Energy and alpha particle to achieve stability

Question 15

Radioactive Decay – Alpha

Answer 15

Large nucleus
Consists of 2 neutrons and 2 protons to from  particle
Is a Helium particle
The element emits Energy and alpha particle to achieve stability

Question 16

Alpha Decay Equation

Answer 16

Atomic mass (p + n)
Atomic number (p)
To find number of neutrons: atomic mass – protons
= 238 - 92=146
n: 146 n: 144 (lost 2 neutrons)
p: 92 p: 90 (lost 2 protons)
emits 2 protons + 2 neutrons that combine to form Helium
To find a tomic mass
= neutrons + protons
= 144+90=234

Question 17

How dangerous is  Decay

Answer 17

‘Least’ (used advisedly) dangerous of all radioactive particles
Heaviest of all decay process products
Travels a few centimetres through air
Cannot pass through a sheet of paper (0.09 mm) A4 (90GSM) is 5g in weight
Cannot penetrate epidermal tissue but can cause erythema(can burn skin)
If emitted inside the body it can cause organ and tissue damage

Question 18

Alpha Particles - Clinical Practice

Answer 18

Cancer Treatment
Inserting sources into cancer masses
Alpha emissions destroy cancer cells
Lacks penetrating power so very localised area of effect
Development of Targeted Alpha Particle Therapy for Solid Tumors
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6930656/
Treatment Secondary Bone Cancer
https://www.macmillan.org.uk/cancer-information-and-support/bone-cancer-secondary/radiotherapy-for-secondary-bone-cancer
Click the link on the landing page for specific information
https://www.cancerresearchuk.org/about-cancer/cancer-in-general/treatment/radiotherapy/internal/radioactive-implant-treatment/what-is-brachytherapy

Question 19

Beta Decay

Answer 19

Unstable atom with too many neutrons or protons
Protons and neutrons can transform into each other
Process to enable stability
Occurs at subatomic level of quarks
UP and DOWN quarks carry fractional charge of the electron
Results in the release of an electron
Electrons released from the nucleus are called Beta Particles 
Two types
Positron +
Negatron -

Question 20

Positron Decay +

Answer 20

Problem: Excess Protons
Solution: Protons transform into a Neutron
Result: Nucleus loses a proton however gains a Neutron
Change in Proton count = change in atomic number
Change in atomic number = change of the original element into another one

Question 21

Positron Decay +

Answer 21

Proton consists of 2 up and 1 down quark
P = U+U+D (2/3)+(2/3)+(-1/3) = 1
Up quark changes to a Down quark
Releases a Positron and a Neutrino
Proton becomes a neutron
N=U+D+D (2/3)+(-1/3)+(-1/3)= 0
Energy is conserved so energy ‘lost’ = 1
Released as Positive Electron / Positron/ +

Remember:
p= UUD
n=UDD
Positron = +
Neutrino = energy particle (v)

Question 22

Positron Decay +

Answer 22

Problem: too many protons
Solution: transform Proton into a Neutron
Result: Mass stays the same - + plus energy
Transforms into a different element

Question 23

Negatron Decay -

Answer 23

Problem: Excess Neutrons
Solution: Neutron transform into a Proton
Result: Nucleus loses a neutron however gains a proton
Release of - Beta Minus
Change in Proton count = change in atomic number
Change in atomic number = change of the original element into another one

Question 24

Negatron Decay -

Answer 24

Neutron consists of 1 up and 2 down quark
N= U+D+D (2/3)+(-1/3)+(-1/3) = 0
Down quark changes to an Up quark
Releases a -1 charge
Neutron becomes a proton
P=U+U+D (2/3)+(2/3)+(-1/3)= 1
Energy is conserved so energy ‘gained’ = -1
Released as negative Electron / negatron/ -

Remember:
p= UUD
n=UDD
Positron = +
Negatron = -
Neutrino = +ve energy particle ()
Anti Neutrino = -ve energy particle ()

n p + - + 

Question 25

Positron Decay -

Answer 25

Problem: too many neutrons
Solution: transform neutron into a proton
Result: Mass stays the same - - plus energy
Transforms into a different element

Question 26

How dangerous is Beta Decay 

Answer 26

Can travel up to a metre through air
Passes through a sheet of paper
Can not penetrate a few mm’s of aluminium sheets
Can penetrate skin but not internal organs (external exposure)
Can be more harmful if ingested or inhaled

Question 27

Clinical use of Beta Decay -

Answer 27

Positron Emission Tomography (PET) Scans
Radionuclide called fluorodeoxyglucouse (FDG) injected
Glucose absorbed faster rate by cancer cells
Beta + decay emissions
Interact with orbital electrons inside body
Annihilation of electron and positron produces gamma rays

Question 28

Gamma Decay 

Answer 28

No particles emitted
High energy gamma ray released
Unstable atom with excess energy
Aims for stable ground state
Atoms remain unchanged
No mass no change just energy
Neutrons and Protons remain unchanged

Question 29

Gamma Decay 

Answer 29

No particle emission
No new element formed
 not charged particles like  or 
No change in number of neutrons or protons
Therefore no change in mass or atomic number

Question 30

Positron Decay -

Answer 30

Problem: too many neutrons
Solution: transform neutron into a proton
Result: Mass stays the same - - plus energy
Transforms into a different element

Question 31

How dangerous is Gamma Decay 

Answer 31

Most ‘dangerous’ type of radiation
Penetrates further (10’s of metres in air)
Travels for longer (more energy)
To reduce the intensity by 50%
75 mm concrete (1.8 m gamma to minimal)
12 mm lead (43 mm gamma to minimal)

Question 32

Stopping Power

Answer 32

alpha paper
beta plastic
gamma lead

Question 33

Clinical Use

Answer 33

Can cause Cancer
Can destroy Cancer cells
Gamma Knife treatment
Diagnostic Imaging – Radioactive Tracer
Technetium 99m
Emission of Gamma Rays