Operating Manual

3130
3.2 Definitions
Radioactivity
The activity of a radioactive source of radiation (isotope) is equal to the number of disinte-
grations per second. The SI-unit is the Becquerel (Bq) and is equal to 1 disintegration per
second. The Becquerel is too small a unit to be used in industrial radiography. Source
strengths are, therefore, quoted in Giga Becquerel (GBq).
1 Curie = 37 GBq, see table 2-3.
Ionisation dose rate
The output of an X-ray set or isotope per unit of time is generally quoted at one metre
distance from the source, and designated in C/kg, see table 1-3.
Ionisation dose
The ionising effect of radiation in one kilogram of dry air is used to define the ionisation
dose. The dose of radiation delivered is equal to the ionisation dose rate multiplied by the
amount of time during which radiation takes place.
The designation used is C/kg.sec.
The output of an X-ray set, however, is quoted in Sievert per hour, measured at 1 metre
distance.
Absorbed energy dose
The radiation energy that is absorbed is expressed in Joules per kilogram (J/kg).
The SI-unit is called Gray (Gy) whereby 1 J/kg = 1 Gy.
Equivalent dose (man dose)
The Sievert (Sv) is the SI-unit for the biological effect of ionising radiation upon man. It
corresponds with the product of the absorbed energy dose gray (Gy) with a factor that has
been experimentally determined and that indicates the relative biological effect (RBE) of
the ionising radiation. For X- and
γ-radiation this factor is equal to one, so that the Sievert
is equal to the Gray.