Radioactivity

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Radioactivity
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Menu

• Background Radiation
• Types of Radiation

• Dangers of Radiation
• Detecting Radiation
• Uses of Radiation
• Radioactive Decay Half life

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Background Radiation
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What is Background Radiation?

• It comes from naturally occurring unstable
  isotopes in.
• The air
• Food
• Building materials
• Rocks under our feet
• Space (Cosmic Rays), and
• Human activity (nuclear explosions, nuclear
  waste)

This is radiation that occurs NATURALLY ALL
AROUND US. It only provides a very small dose
altogether so there should be no danger to our
health
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The Proportion of Sources of Background Radiation
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The Level of background radiation changes
depending on where you are
At high altitudes (e.g. On a jumbo jet) it
increases because of more exposure to cosmic rays
. LESS ATMOSPHERE TO PROTECT US!
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This is a major problem for astronauts that fly
above the Earths atmosphere (on the
International Space Station for example)
A number of astronauts have suffered from cancer
as a result.
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• The astronauts that will be chosen to go to Mars
  will be OLDER than usual. This is because they
  are more experienced and also because they will
  be exposed to far more radiation than their
  bodies can be protected from

They know that they are likely to die of cancer
within 10 years of their return to Earth
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People who work in underground mines will receive
more radiation as a result of the rocks giving
off radiation all around them.
It is the natural decay of radioactive isotopes
that makes the earth hotter as you go deeper down
a coal mine.
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The coloured areas indicate where there is more
radiation given off by the rocks.
These are usually associated with igneous rocks
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Background Radiation Count Must Always Be Taken
Away If You Want to Measure the Radioactivity of
a Sample
Radioactivity is measured in Becquerel (Bq) One
Becquerel is one nucleus decaying per second
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This is Madame Curie and her husband. They both
died of cancer because of the radioactive
materials. The books they used are SO
radioactive that they have to be kept in lead
containers.
If a scientist wants to read them they have to
wear full lead protection!
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Nuclear Processes Release More Energy Than
Chemical Processes
When a nucleus splits it gives out a lot more
energy than a chemical bond. This is why nuclear
bombs release a lot more energy than other bombs
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What Are the Types of Radiation?
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What are the 3 types of radiation?

• ALPHA PARTICLES
• BETA PARTICLES
• GAMMA RAYS

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A radioactive substance can emit one of the
following types of radiation. A simple way to
distinguish between them is their ability to be
absorbed by different types of material.
Alpha absorbed by thin sheet of paper (or few
cms of air) Beta Absorbed by a few mms of
aluminium Gamma VERY penetrating needs several
cms of lead
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What are ALPHA PARTICLES?

• They are relatively big, heavy slow
  moving and cause a large amount of ionisation
• They therefore dont travel far into materials
  but are stopped quickly
• They are made up of 2 protons and 2
  neutrons and are actually helium nuclei

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What are BETA Particles?

• These can penetrate quite well
• They are fast moving electrons with small
  mass
• They cause a small amount of ionisation

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What are GAMMA Rays?

• These are the opposite of alpha particles in a
  way!
• They penetrate a long way into materials
  without being stopped
• They cause little ionisation
• They are high energy Electromagnetic waves with
  a very short wavelength

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Type Alpha Particles Beta Particles Gamma Rays
Description 2 protons 2 neutrons electron e.m. wave
Charge - No charge
Mass Heavy in comparison Very light
Speed 1/10th speed of light 9/10th speed of light Speed of light
Ionizing Effect strong weak Very weak
Penetrating Effect Not very (stopped by paper) Penetrating (stopped by 5mm of aluminium) Highly penetrating
Effect of Electric Magnetic Fields Bent by electric magnetic fields Bent strongly by electric magnetic fields Not bent by electric magnetic fields
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These are the tracks left by radiation in a
bubble chamber
How many different types of tracks can you see?
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Dangers of Radiation
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Alpha, Beta and Gamma Radiation will harm living
cells. When they enter the cells they collide
with the molecules and cause ionisation. Lower
doses usually cause minor damage to the cell and
can result in mutant cells that divide
uncontrollably. This is CANCER.
Higher doses tend to kill the cells completely,
which causes radiation sickness.
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What is IONISATION?
This is when radiation collides with neutral
atoms or molecules, altering their structure by
knocking out electrons.
Alpha Particle
This leaves them as IONS or CHARGED PARTICLES.
Electron
Neutral atom or molecule
Ion
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• The extent to which your cells are damaged
  depends on
• How long you are exposed to the source and
• How strong the radiation source is.

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Dangers of Radioactivity
Radiation ionises atoms in living cells this
can damage them and cause life threatening cancer
or leukaemia.
OUTSIDE the body Beta Gamma radiation are more
dangerous as Alpha radiation is blocked by the
skin. INSIDE the body an Alpha source causes the
most damage because it is the most ionising.
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The Safety Precautions In The Laboratory Are-

• Never allow skin contact
• Keep the source pointing away from you ( and
  others!)
• always keep the source in the lead box

It is assumed that you would not be eating,
drinking or smoking at the same time as this
would take the radiation inside your body!
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We Can Detect Radiation Using Photographic Film
This Dosage Monitor contains photographic film
shows how much radiation the wearer has been
exposed to
You will often see people in hospitals wearing
these
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We can also detect radiation with a Geiger
Counter
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Extra precautions for Nuclear Radiation workers.
Wear full protective suits to stop tiny
particles getting into your lungs or underneath
your nails
Use remotely controlled robot arms
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Uses of Radiation
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How can radioactivity be used for thickness
control?
Rollers
Beta Detector
Paper
Beta Emitter
If paper thickness becomes too great less
radiation passes through to detector which sends
a signal to the rollers to move closer.
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Radiation can be used as a TRACER to see how
the body is functioning
To avoid it getting out of hand like this
Overactive Thyroid Gland
For example the Thyroid Gland absorbs Iodine
If radioactive Iodine is injected into the
patient, we can see how much iodine is absorbed
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Tracers Can Also Be Used in Industry To-

• Detect leaks in pipes
• to show flow rates
• to show uptake of fertilizers in plants

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Radiation can be used to
..and to date an Egyptian mummy
Kill mould and bacteria on your strawberries
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Radioactive Decay Half Life
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This is the TURIN SHROUD. It has been radiocarbon
dated to find out its age.
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Half Life
The Radioactivity of a sample always decreases
over time
HALF LIFE is the TIME TAKEN for HALF of the
radioactive atoms now present to DECAY
How quickly the activity of a radioactive sample
drops varies from one sample to another. It may
take hours or millions of years
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How do we measure Half Life?
You can use a graph to work out Half Life Or you
can calculate it step by step
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A Radioactive Decay Graph
Count Rate
800




Radioactivity of Sample
600
400
200
One Half Life
One Half Life
One Half Life
0
Time
0 4 8 12
16 20
1 half life
Time in Hours
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Half Life Calculations
The radioactivity of a simple isotope is 640
counts per minute. Two hours later it has fallen
to 40 counts per minute. Calculate the half Life
of the sample.
After three Half Lives 80
Initial count 640
After one Half Life 320
After two Half Lives 160
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2
2
2
Two Hours for 4 Half Lives. Therefore half Life
is 30 Minutes
After four Half Lives 40
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