Transcript Document

Radioactivity 5
Uses of radioactive sources
LOJ Feb 2004
Using Gamma Rays
• A patient is injected with a
radioactive tracer that emits
gamma rays.
• The gamma ray is electromagnetic
radiation of very high penetration
power.
LOJ Feb 2004
Using Gamma Rays
• Therefore more rays exit the body
and are available for detection than
interact with the patient's tissue.
• These can be detected by a gamma
camera and the concentration of
radioactive tracer in various parts of
the body can be ascertained.
LOJ Feb 2004
LOJ Feb 2004
Radiotherapy
• Smoking kills – in a
terrible way
sometimes - the image
on the next slide
shows a smoking
related oral cancer
emerging from the
throat of the patient
in its late stage
LOJ Feb 2004
Radiotherapy
• High doses of
ionizing radiation
can kill cells;
• They are used to
kill cancer cells
and harmful
microorganisms.
LOJ Feb 2004
Radiotherapy
• Tumours can be treated
using gamma rays
(nuclear radiation) or
high energy X-rays
(which can have the
same wavelength as
gamma rays – but are
not from the nucleus).
LOJ Feb 2004
Definition: tumour n. (US
tumor) a swelling, especially
from an abnormal growth of
tissue, whether benign or
malignant.
It comes from the Latin tumor
from tumere ‘ to swell’
Radiotherapy
• Cells that divide rapidly
are more prone to damage
by high-energy
electromagnetic radiation.
• This means that tumour
cells are more
radiosensitive than their
normal counterparts.
LOJ Feb 2004
Definition: tumour n. (US
tumor) a swelling, especially
from an abnormal growth of
tissue, whether benign or
malignant.
It comes from the Latin tumor
from tumere ‘ to swell’
Radiotherapy
• By carefully aiming the rays
at the tumour (gamma-ray
beams directed from a
multitude of angles that
result in the maximum
gamma ray intensity within
the tumour) the harmful
effect of the ionising
radiation is kept to a
minimum in the surrounding
tissue.
LOJ Feb 2004
Radiotherapy
• This kind of treatment
is most hazardous
when a brain tumour is
being irradiated and
the surrounding tissue
is vital for normal
brain function.
LOJ Feb 2004
Radiotherapy
• Several treatments are
usually given over a time
period of several weeks
to minimise the
unpleasant side effects
(most commonly nausea,
sickness, and tiredness).
LOJ Feb 2004
Radiotherapy
• New methods of delivering
radiation treatment have
been developed
– Interstitial radiation
involves implanting radioactive
chemicals (termed seeds)
directly into a tumour.
– Stereotactic radiosurgery
delivers a high, single dose of
radiation to a small, welldefined area.
LOJ Feb 2004
Sterilisation of Food and
Surgical Instruments
• Food and surgical instruments can
be irradiated with gamma rays to
sterilize them
• Gamma rays kill bacteria.
Therefore irradiating food or
surgical instruments is a good way
of ensuring they are sterile.
LOJ Feb 2004
Sterilisation of Food and
Surgical Instruments
• The gamma rays penetrate packaging,
so the food or instrument can be
sealed and then sterilized so that recontamination cannot occur.
• No radioactive source particles are
allowed to get in touch with the
irradiated substance.
• The source is sealed so that only
gamma rays get out. Therefore the
irradiated substance is sterile but
NOT radioactive.
LOJ Feb 2004
As radiation passes through a
material it can be absorbed.
• The greater the thickness of a
material the greater the absorption.
• The absorption of radiation can be
used to monitor/control the thickness
of materials.
LOJ Feb 2004
The absorption of radiation can be
used to monitor/control the
thickness of materials
• The more radiation
that gets through,
the thicker the
barrier must be.
• Circuitry can
automatically adjust
the roller settings
so that a constant
count is attained.
LOJ Feb 2004
Alpha Uses
Long half life:
• Dating of rocks using
Uranium-238/lead ratios
• Smoke detectors
• Gas lamp mantles
• Nuclear batteries
LOJ Feb 2004
Beta Uses
Short half life
• Tracers in industry - detecting
leaks in pipes
Long half life
• Thickness control of very thin
metal sheets, paper or cardboard in
manufacturing and industry
• C-14 dating
• Emergency sign lighting
LOJ Feb 2004
Gamma Uses
Short half life
• Medical tracer used with gamma
camera
• Tracers in
industry detecting routes
of underground
rivers and
streams
LOJ Feb 2004
Gamma Uses
Long half life
• High activity - radiotherapy
• High activity - sterilization of medical
surgical instruments
• High activity - irradiation of food to kill
bacteria and prolong shelf life
• Thickness control of metal sheets (when
too thick for beta) in manufacturing and
industry
• Checking welds
LOJ Feb 2004
Other Uses
• Leaks from a pipeline can be
traced by adding a radioactive
isotope into what ever it is
carrying. The source must have a
short half-life (a few hours) so
that it can be detected as it
passes through but not stay
radioactive long enough to pose a
health hazard.
LOJ Feb 2004
Other Uses
• Wear of moving parts can be tested
by making the part radioactive and
monitoring the proportion of worn
parts in the lubricating oil by looking
for the level of radioactivity in it.
• A gamma source can be used to check
welds in metal parts. It is used in a
similar way to X-rays on a human
body. A photographic plate is placed
behind the weld. It is exposed more
where the weld is weak.
LOJ Feb 2004
Nuclear Batteries
• The Apollo Moon missions used a radioisotope
thermal generator (RTG).
• A rod of plutonium-238 weighing approximately
2.5 kilograms provides a thermal power of
approximately 1250W. Plutonium-238 is a nonfissile isotope of plutonium that decays by alpha
particle emission with essentially zero associated
gamma emissions.
LOJ Feb 2004
Smoke Detectors
• Some smoke detectors contain a small
amount of Americium-241, an alpha
emitter (an low energy gamma emitter)
with a half life of 460 years.
• They consist of an ionization chamber
linked to a simple electronic alarm circuit.
LOJ Feb 2004
Smoke Detectors
• The Americium ionizes the air between
the plates, causing a current to flow.
• Smoke entering the detector absorbs
some extra alpha particles than the air
would , lowering the current, and
triggering the alarm.
LOJ Feb 2004