P6 Radioactive Materials

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26/05/2016
P6 Radioactive Materials
OCR 21st Century
M Barker Shirebrook Academy
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P6.1 Why are some materials radioactive?
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The structure of the atom
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Introduction to Radioactivity
Some substances are classed as radioactive
this means that they are unstable and
continuously give out radiation at random
intervals
Radiation
The nucleus is more stable after emitting some
radiation this is called radioactive decay.
This process is NOT affected by temperature or
other physical conditions.
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Background Radiation
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Structure of the atom
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A hundred years ago people thought that the atom
looked like a plum pudding a sphere of
positive charge with negatively charged electrons
spread through it
Ernest Rutherford, British scientist
I did an experiment (with my colleagues Geiger
and Marsden) that proved this idea was wrong. I
called it the Scattering Experiment
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The Rutherford Scattering Experiment
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Alpha particles (positive charge, part of helium
atom)
Thin gold foil
Most particles passed through, 1/8000 were
deflected by more than 900
Conclusion atom is made up of a small,
positively charged nucleus surrounded by
electrons orbiting in a cloud.
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What keeps a nucleus together?
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The strong force
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Nuclear Fusion in stars
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Nuclear fusion happens in stars when hydrogen
nuclei are brought close enough together
Proton
Neutron
We can calculate how much energy this reaction
releases using my famous Emc2 equation.
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Isotopes
An isotope is an atom with a different number of
neutrons
A radioisotope is simply an isotope that is
radioactive e.g. carbon 14, which is used in
carbon dating.
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Types of radiation
1) Alpha (?) an atom decays into a new atom
and emits an alpha particle (2 protons and 2
______ the nucleus of a ______ atom)
Unstable nucleus
New nucleus
Alpha particle
2) Beta (?) an atom decays into a new atom by
changing a neutron into a _______ and electron.
The fast moving, high energy electron is called a
_____ particle.
Beta particle
Unstable nucleus
3) Gamma after ? or ? decay surplus ______ is
sometimes emitted. This is called gamma
radiation and has a very high ______ with short
wavelength. The atom is not changed.
Words frequency, proton, energy, neutrons,
helium, beta
Unstable nucleus
New nucleus
Gamma radiation
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Blocking Radiation
Each type of radiation can be blocked by
different materials
Sheet of paper (or 6cm of air will do)
Few mm of aluminium
Few cm of lead
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Changes in Mass and Proton Number
Alpha decay
237
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93
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Beta decay
90
0
-1
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A radioactive decay graph
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Activity (Bq)




Time
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Half life
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The decay of radioisotopes can be used to measure
the materials age. The HALF-LIFE of an atom is
the time taken for HALF of the radioisotopes in a
sample to decay
After 3 half lives another 2 have decayed (14
altogether)
After 2 half lives another half have decayed (12
altogether)
After 1 half life half have decayed (thats 8)
At start there are 16 radioisotopes
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A radioactive decay graph
26/05/2016
Count




Time
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P6.2 Using Radioactive Materials
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Ionisation
Radiation is dangerous because it ionises atoms
in other words, it turns them into ions by
knocking off electrons
Alpha radiation is the most ionising (basically,
because its the biggest). Ionisation causes
cells in living tissue to mutate, usually causing
cancer, and causes molecules to break into bits
called ions that then take part in other
reactions.
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Uses of Radioactivity 1
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Sterilising medical instruments
Gamma rays can be used to kill and sterilise
germs without the need for heating. The same
technique can be used to kill microbes in food so
that it lasts longer.
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Uses of Radioactivity 2 - Tracers
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A tracer is a small amount of radioactive
material used to detect things, e.g. a leak in a
pipe
The radiation from the radioactive source is
picked up above the ground, enabling the leak in
the pipe to be detected.
Tracers can also be used in medicine to detect
tumours
For medicinal tracers, you would probably use a
beta source with a short half life why?
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Uses of Radioactivity 3 - Treating Cancer
26/05/2016
High energy gamma radiation can be used to kill
cancerous cells. However, care must be taken in
order to enure that the gamma radiation does not
affect normal tissue as well. Radioactive iodine
can be used to treat thyroid cancer. Iodine is
needed by the thyroid so it naturally collects
there. Radioactive iodine will then give out
beta radiation and kill cancerous cells.
What sort of half life would you want the
radioactive iodine to have?
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Exposure to Radiation
People like me work with radiation a lot so we
need to wear a dosimeter to record our exposure
to radiation
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Background Radiation by Location
In 1986 an explosion occurred at the Chernobyl
nuclear power plant. Here is a radiation map
showing the background radiation immediately
after the event
Other risky areas could be mining underground,
being in a plane, working in an x-ray department
etc
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How we are exposed to Radiation
We can be exposed to radiation by irradiation
or by contamination
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Nuclear fission
New nuclei (e.g. barium and krypton)
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Chain reactions
Each fission reaction releases far more energy
than burning the same mass of coal would do!
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Fission in Nuclear power stations
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Disposing of radioactive waste
The key to dealing with radioactive waste is to
IMMOBILISE it. There are a number of ways of
doing this depending on how __________ the waste
is
High level waste is immobilised by mixing with
____ making ingredients, melting and pouring the
glass into steel containers.
Intermediate waste is set in cement in _____
drums.
Words glass, steel, underground, radioactive