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3.5.10 Activable Stable Tracers

Activable stable traces are used as alternatives to ra-
dioyracers where it would be unacceptable to use ra-
dioactvity, in the environment, in humans or in coun-
tries where legislative practices prevent it. The reason
for using a stable tracer can also be that no radioac-
tive tracer of suitable half-life exist. The purpose of the
stable tracer is to provide an easily activated material,
which is not found in the materials to be studied and
which is very sensitive to the determination by NAA.
Any suitable element may be used as tracer, prefer-
ably one which produces nuclides with a short half-life
(for rapid irradiation and counting) and with a high sen-
sitivity for activation.

An example of the use of a stable tracer is to mea-
sure the effectiveness of a spraying machine in agri-
cultural use for treating crops with pesticided. A suit-
able element is dysprosium which is relatively rare in
the environment, has a radionuclide with a half-life of
1.6 minute which can detected down to 10 ng. Stable
tracers are also used in medical studies, for example
to follow the absorption of iron through the human gut.
In this case an enriched isotope,Fe-58, is fed in the
diet and then the Fe-58 collected in the faeces is acti-
vated for analysis. In the study of water flow in lakes or
the sea, indium has been favourablely used as an ac-
tivable traver. When long transport distances over long
time intervals need to be studied the use of a stable

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