12.1 Basics and Guidelines
106
Distance
This means the distance between the radioactive source and the human body.
The radiation intensity (dose rate) decreases - like light - in proportion to the
square of the distance, i.e., doubling the distance to the source reduces the dose
rate to one quarter.
Conclusion:
When handling radioactive substances, maximum dis-
tance to the source should be maintained. This is es-
pecially true for persons that are not directly involved
in this work.
Time
The total time a person stays in the vicinity of a radiometric measuring system
and the body is exposed to radiation. The effect is cumulative and increases
therefore with the duration of the radiation exposure.
Conclusion:
Any work in the vicinity of radiometric measuring
system has to be prepared carefully and organized
such that it can be carried out in the shortest time
possible. Having the proper tools handy is of particular
importance.
Shielding
The shielding effect is provided by the shielding material surrounding the source.
As the shielding effect depends, following an exponential function, on the prod-
uct of thickness multiplied by the density, it follows that material with a high
specific weight will normally be used for shielding. Suitable dimensions are usu-
ally calculated by the supplier.
Conclusion:
Before installing or dismantling the shielding, make
sure that the radiation exit channel is closed. The
source must not be removed from the shielding and
not remain unshielded.
DISTANCE
TIME
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