introduction to radioactivity Flashcards

1
Q

Atomic Structure

A

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

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2
Q

Nucleons:Protons and Neutrons

A

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

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3
Q

Strong Nuclear Force

A

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

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4
Q

Two Types of Nuclear Force

A

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

Weak Nuclear Force
Responsible for Radioactive Decay

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5
Q

Strong Nuclear Force (SNF)

A

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

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6
Q

What is an ISOTOPE

A

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

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7
Q

Radioactive Decay

A

Also Known as:
Nuclear Decay
Radioactivity
Radioactive Disintegration
Nuclear disintegration

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8
Q

What is Radioactive Decay?

A

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 ()

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9
Q

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

A

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

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10
Q

Units of Activity

A

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

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11
Q

Radioactivity in Radiography

A

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

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12
Q

Radio-isotope Diagnostic Radiography

A

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

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13
Q

Radioisotope Iodine

A

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

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14
Q

Radioactive Decay – Alpha

A

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

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15
Q

Radioactive Decay – Alpha

A

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

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16
Q

Alpha Decay Equation

A

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

17
Q

How dangerous is  Decay

A

‘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

18
Q

Alpha Particles - Clinical Practice

A

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

19
Q

Beta Decay

A

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 -

20
Q

Positron Decay +

A

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

21
Q

Positron Decay +

A

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)

22
Q

Positron Decay +

A

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

23
Q

Negatron Decay -

A

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

24
Q

Negatron Decay -

A

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 + - + 

25
Positron Decay -
Problem: too many neutrons Solution: transform neutron into a proton Result: Mass stays the same - - plus energy Transforms into a different element
26
How dangerous is Beta Decay 
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
27
Clinical use of Beta Decay -
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
28
Gamma Decay 
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
29
Gamma Decay 
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
30
Positron Decay -
Problem: too many neutrons Solution: transform neutron into a proton Result: Mass stays the same - - plus energy Transforms into a different element
31
How dangerous is Gamma Decay 
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)
32
Stopping Power
alpha paper beta plastic gamma lead
33
Clinical Use
Can cause Cancer Can destroy Cancer cells Gamma Knife treatment Diagnostic Imaging – Radioactive Tracer Technetium 99m Emission of Gamma Rays