Transcript 1 - MACscience

DETECTION & USES
OF RADIATION
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DETECTION OF RADIATION
1. PHOTOGRAPHIC FILM
Small packets of photographic emulsions are routinely
used by workers to monitor radiation exposure.
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2. CLOUD CHAMBERS
Used to track charged particles, it contains a vapour, usually an
alcohol. The vapour is cooled so that it becomes supersaturated.
A charged particle enters the chamber and ionises air or alcohol
vapour atoms. Vapour in the chamber condenses around these
ions, forming droplets. The droplets are what form the trail.
More information about the particles that
are present can be found out by placing
the chamber in a magnetic field.
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CLOUD CHAMBERS
ALPHA TRACKS
BETA TRACKS
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3. IONISATION CHAMBERS
μA
radiation
-
- -
+
+ +
+ +
Radiation ionises the air between the metal plates.
This provides a mechanism for a current to flow.
The ionisation current is proportional to the
intensity of the radiation.
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4. GEIGER MÜLLER TUBE
The tube is filled with Argon gas at low pressure. About +400 Volts are applied
to the thin wire in the middle. When a particle enter the tube, it ionises an
Argon atom. The electron produced is attracted to the central wire anode, at
high speed and ionises further Argon atoms, causing an "avalanche". Thus
one single incoming particle will cause many electrons to arrive at the anode,
creating a pulse which can be amplified and counted.
+ve 400V
source
0V
+ve 450V
R
tube
C output
0V
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5. SMOKE ALARM
Americium source
emits ionising alpha
particles which pass
through the mesh.
Am-241
-
-- -
+
+ + ++
+ +
Radiation ionises the air
between the metal plates.
This provides a mechanism
for a current to flow.
Smoke particles attach to the charged ions and
restore them to a neutral electrical state. This
reduces the flow of electricity between the two
plates in the ionization chamber. When the
electric current drops below a certain
threshold, the alarm is triggered.
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6. DETECTION OF CRACKS AND
LEAKS
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7. MONITORING THICKNESS
DETECTOR
RADIOACTIVE
SOURCE
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“THE ICE MAN” FOUND IN A MELTING AUSTRIAN GLACIER IN 1991
RADIO CARBON – C14 DATING
DATED USING 8.
TO THE COPPER AGE, 5300 YEARS OLD
Nitrogen 14 atoms in the atmosphere absorb neutrons that have been
released by cosmic bombardment.
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N  n N  C  H
1
0
15
7
14
6
1
1
Carbon 14 is a beta (–) emitter,
half life about 5600 year
One carbon 14 atom exists in nature for
every 1,000,000,000,000 Carbon 12
0
C14
N

7
1 e  e
14
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Plants and animals which utilise carbon in biological foodchains take up C-14 during their
lifetimes. They exist in equilibrium with the C14 concentration of the atmosphere, that is,
the numbers of C14 atoms and non-radioactive carbon atoms stays approximately the
same over time. As soon as a plant or animal dies, they cease the metabolic function of
carbon uptake; there is no replenishment of radioactive carbon, only decay. A carbon 14
count enables an analyst to determine when the sample died.
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9. FOOD IRRADIATION
Cobalt 60
GAMMA RAYS
The gamma rays passing through
the food is enough to destroy
many disease-causing bacteria as
well as those that cause food to
spoil, but is not strong enough to
change the quality, flavour or
texture of the food.
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Radio isotopes to be used as 10. TRACERS
are produced by neutron bombardment in a
nuclear reactor.
e.g. Sodium 24 is made by bombarding
sodium with neutrons
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Na n Na
1
0
24
11
Sodium 24 is a beta/gamma emitter and is
used to trace blood circulation in animals.
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Agriculture: Radioactive isotopes are used as tracers in
plants. Radioisotopes are added to fertiliser in small but
known quantities. The uptake of the fertiliser can be measured
by the researcher measuring how radioactive a plant has
become. This technique is largely a research tool.
Examples of isotopes used for this purpose include
phosphorous32 and nitrogen15.
radio
phosphorous
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11. MEDICAL USES
THERAPEUTIC
Normal Cells
DIAGNOSTIC
Cancer Cells
High-energy radiation from x-rays,
gamma rays or neutrons is used
to kill cancer cells and shrink
tumours. Radiation may come
from a machine outside the body
(external-beam radiation therapy),
or it may come from radioactive
material placed in the body near
cancer cells (internal radiation
therapy, implant radiation).
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Tracers
In tracer techniques a radioactive
isotope, such as Technetium 99m,
is injected into the body. The
signals coming from the ensuing
radiation can be detected with a
gamma camera.
PET scans A radio isotope which
decays by positron emission, is
injected. When a positron encounters an
electron they annihilate each other,
emitting two photons. The energy and
path of these photons leaving the body
can then be used to give an accurate
picture of the area where the isotope
was absorbed.
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12. PEST CONTROL
MEDFLY
Mediterranean Fruit Fly
The Sterile Insect Technique (SIT) involves producing
a large number of insects then irradiating them with
gamma radiation before hatching, to sterilise them.
The sterile males are then released in large numbers
in the infested areas. When males mate with females,
no offspring are produced. Repeated releases of
sterilised males ensures the population of the insect
pest in a given area is drastically reduced.
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There is also… BACKGROUND
RADIATION (UK)
OTHER 0.2%
NUCLEAR POWER &
WEAPONS 0.3%
COSMIC 10%
FOOD & DRINK
11.5%
RADON
50%
MEDICAL 14%
GROUND &
BUILDINGS 14%
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