Download Radioactivity

KS4 Physics
Radioactivity
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Contents
Radioactivity
Background radiation
Safety rules
Types of radiation
Uses of radiation
Summary activities
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Uses of radiation
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Sterilization
Gamma rays are used to kill bacteria, mould and insects in
food. This can be done even after the food has been
packaged. It can affect the taste, but supermarkets like it
because it lengthens the shelf life.
unsterilized
gamma source
sterilized
Gamma rays are also used to kill bacteria on hospital
equipment. It is particularly useful with plastic equipment that
would be damaged by heat sterilization.
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Radiotherapy
A carefully controlled beam of gamma rays can be
used to kill cancer cells. It must be directed carefully to
minimize the damage to normal cells.
However, some damage is unavoidable and this can
make the patient ill.
It is therefore a balancing act – getting the dose high
enough to kill the cancerous cells, but as low as
possible to minimize the harm to the patient.
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Leak detection in pipes
A radioactive isotope is injected into the pipe. Then the outside
of the pipe is checked with a Geiger-Müller detector, to find
areas of high radioactivity. These are the points where the pipe
is leaking. This is useful for underground pipes that are hard to
get near.
The isotope must
have a short halflife so the material
does not become a
long-term problem.
The radioactive isotope must be a gamma emitter so that
it can be detected through the metal and the earth where
the pipe leaks. Alpha and beta rays would be blocked by
the metal and the earth.
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Thickness control mill
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beta source
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Electronic instructions to adjust rollers.
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Detecting radiation
What are the different methods of detecting radiation?
Geiger-Müller tube
spark counter
photographic film
cloud chamber
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Photographic film
1. What happens to film when it is exposed to radiation?
It darkens.
2. Can photographic film tell you the type of radiation that it
has been exposed to?
No, just the amount of radiation received.
3. What can this be used for?
Can be used in radiation badges, which record the
exposure of workers to radiation. Different windows on
the badge detect different types of radiation.
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Geiger-Müller tube
The detector is a metal tube filled with gas. The tube has a thin wire
down the middle and a voltage between the wire and the casing.
It is good at detecting alpha and beta radiation, but not as good
at detecting gamma radiation.
collision & ionization
radiation
argon gas
mica window
When the radioactivity enters the tube,
it ionizes the gas in the tube. This
produces a pulse of current, which is
amplified and passed to a counter.
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counter
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Spark detector
A spark detector consists of a metal grid and a metal strip. A
high voltage is applied between the grid and the strip. The
voltage is increased until electrical arcing (sparking) across
the gap just occurs.
When ionizing radiation is placed close to the detector there
is a marked increase in the amount of sparking.
Which type of radiation
will be detected most
easily?
high-voltage
supply
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Why?
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Cloud chamber
Cloud chambers show the actual paths of the ionizing particles.
They rely on ionization. The cloud chamber is cooled and is then
super-saturated with alcohol.
When an ion is formed a droplet of condensation appears. Cloud
chambers are good for showing alpha radiation as this is the most
ionizing. Beta radiation shows faint traces. Cloud chambers are not
good for showing gamma radiation, as it is only weakly ionizing.
radioactive
source
cooled
alcohol
vapour
solid carbon dioxide
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Contents
Radioactivity
Background radiation
Safety rules
Types of radiation
Uses of radiation
Summary activities
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Glossary
 alpha radiation – Positively charged particles made up of
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two protons and two neutrons. It is the least penetrating of the
three main types of radiation.
background radiation – Constant low-level radiation
from food and environmental sources.
beta radiation – High-energy electrons emitted by some
radioactive materials. It is more penetrating than alpha
radiation but less penetrating than gamma radiation.
cloud chamber – A device that shows the paths of
ionizing particles. It is good at detecting alpha radiation.
gamma radiation – Short wavelength electromagnetic
radiation emitted during radioactive decay. It is the most
penetrating of the three main types of radiation.
Geiger-Müller tube – A device used to detect and
measure radiation from radioactive materials.
ionizing radiation – High-energy radiation capable of
ionizing substances through which it passes.
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Anagrams
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Multiple-choice quiz
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