Page 20 - Curriculum Visions Dynamic Book

Radioactive tracers
Many radioactive materials are used to trace
how chemical reactions have taken place, what happens to materials in nature and what happens inside the body. These are called radiotracers.
The important factor in the use of radiotracers is that both a radioactive isotope and its stable counterpart behave in much the same way in
the environment. And because radiotracers can be detected at extremely low concentrations (sometimes down to one part
in a trillion), it is possible to tag material with radiotracers even for such sensitive investigations as medical diagnosis.
A wide range of tracing isotopes is available for use. In farming research, for example, scientists label fertilisers with radioactive nitrogen, potassium or phosphorus to examine how plants take up nutrients from the soil.
In medical diagnosis, radioactive iodine is used by doctors to work out how fast iodine is taken up by the thyroid gland. Our bodies need some iodine, and when the rate is low, people may suffer from goitres and other problems.
Radioactive technetium, a synthetic element, is used by doctors to find out how various organs work. For example, doctors can inject
it into the bloodstream to find the location
of brain tumours.
Sodium, as salt, is naturally present in the blood supply. Radioactive sodium is used
to trace the way the blood flows through
the arteries and veins. Radioactive strontium (which behaves like calcium in the bones)
is used to trace bone growth.
Detecting pollution
Radiotracers are widely used to monitor the behaviour of pollutants in the environment. A small amount of radiotracer added to the discharge of a factory, for example, presents no health hazard in itself, and the tracer can be used to examine what happens to
the effluent.
Tracing holes in metal
Companies that make high precision metalwork such as aircraft engines need to check to make sure there are no tiny holes in the metal they use or the welds they have made. X-ray examinations are often used for this purpose. Because X-rays are absorbed by metal, they cannot be used to examine very thick metals. In these cases, it is sometimes possible to look at the way oil behaves in an engine by using neutron radiography techniques.
In this method a source of neutrons is used. Neutrons are absorbed by any hydrogen- containing material, such as oil, so even tiny leaks will show up as a change in the absorption of neutrons. Thus, possible leaks can be traced.
 Radioactive xenon can be used as a tracer for medical use. In this picture the patient is inhaling a gas mixture which includes radioactive xenon. This will concentrate in the blood vessels of the brain. Detectors in the helmet which is placed over the patient’s head trace the gamma rays emitted by the tracers, and a computer is used to interpret the data and create a graphic image of the circulation in the patient’s brain, as can be seen on the computer monitor in the background.
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