BERTHOLD TECHNOLOGIES Uni-Probe LB 490 - Page 35

Uni-Probe LB 490
BERTHOLD TECHNOLOGIES GmbH & Co. KG
1 – 35
Volume 1 6 Radiation Protection
1
6.3.3 Radiation Dose Calculations
When preparing work on radiometric measuring systems, it is
important to pre-calculate the radiation exposure to be expected,
since this has consequences on the required safety precautions.
The expected radiation exposure can be calculated quite easily and
with sufficient accuracy, provided you know the isotope and the
activity of the source used. You can take this information from the
source documentation, or from the type label on the shielding.
The radiation exposure to be expected for a shielded source is cal-
culated as follows:
A is the activity of the source and k the respective specific Gamma
radiation constant (see table below). The distance from the mea-
suring point to the source is r and the duration of stay at this point
is T. s is the shielding factor of the shielding used; it is listed in the
shielding brochure or can be calculated. s = 1 when calculating the
dose rate for work with an unshielded source.
Calculation example The dose in a distance of 50cm from a Co-60 source with an activ-
ity of 350MBq and a time of 30minutes has to be calculated. The
source is installed in a shielding with a shielding factor of 30:
Nuclide K Dimensions
Co-60 0.35
Cs -137 0.09
Dosis D
AkT××
r
2
s×
-----------------------=
μSvm
2
×
h MBq×
-------------------------
D
350MBq 0.35μSv m×
2
0.5h××
0.5m()
2
hMBq× 30××
-------------------------------------------------------------------------------------------- 8.2μSv==