Version No. 1.1
Page 6 of 51 User Manual STS Safe Series all Equipment 2023 V1.1
4.2 Inverse Square
The Safe-Series has been designed to provide as realistic as possible response to the Inverse Square
Law. Radiofrequency is by its nature governed by the principle of 1/D2 so the simulators start from a
position of strength. It is however impossible to recreate the full characteristics of gamma radiation
and so there are other factors which will influence the instruments response. These include
reflections, materials used in casings and materials in the local environment where the instrument is
being used. These factors will all have some effect on the accuracy of the inverse square
representation, the instruments software does compensate for some of this loss through reflections
and the end result is very close to the expected relationship.
4.3 Attenuation
Attenuation by Materials
The wavelength selected for use in the Safe-Series was chosen because it provides the best
simulation of ionising radiation attenuation. At this wavelength, most common building materials
provide approximately the same attenuation for ionising radiation (Cs 137) as does the simulator,
using its radiofrequency signal.
In particular, wood, glass, brick, concrete and plasterboard all have appropriate attenuation
characteristics.
Metals of any thickness totally attenuate the radiation field although due to reflected signal it is
possible for some of the signal to leak out of containers which are not fully sealed.
For training purposes it is suggested that sources are placed in plastic, wood or card containers if the
source is to be concealed. That said the source can be successfully hidden in vehicles without any
issues.
4.4 Field Pattern
The Safe-MiniSource has been specifically designed to generate as near an isotropic field as is
possible. The use of advanced antennae design and sophisticated software enables a field to be
generated in three different axis and thus forms a virtually complete sphere or radiated signal. Some
factors may cause imperfections in the field pattern such as large metal objects which cause
significant reflection of the signal, or other objects between the detector and the signal generator.
These are however minor imperfections and should not greatly affect the received signal on the
Survey Meter or Dosimeter.
4.5 Polar Response
The Survey-Safe and Dosi-Safe instruments have also been specifically designed to eliminate loss
of signal seen when the instrument is pointed away from the source. The unique system of Antennae
in the instrument allows for the instrument to face in any direction and still receive the signal
generated by the Safe-MiniSource. As with real instruments there is some minor loss when the
instrument is pointing 180 degrees away from the source but unlike other systems the signal is not
lost altogether.
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