LB 124 Scint 8. Basis of Calculation
83
8.6 Bq-Calculation and Determination of the Calibration Factors
The explanation of the basic principles of the Becquerel calcu-
lation is not only of a documentary nature, but is meant to en-
able you to determine calibration factors for contamination mea-
surements for further nuclides, which are not part of the nuclide
library of the LB 124 Scint. For this purpose, the two free entry
positions B1 and B2 are provided (see chapter 6).
To be able to convert counts per second into decays per sec-
ond per cm
2, the constant K has to be determined according to
the formula
Bq/cm
2
= K x cps
for each nuclide and for each type of detector.
Bq/cm
2 = area activity
K = conversion constant Bq x s per cm
2
Cps = counts per second measured
For the determination of K, a calibrating source with known ac-
tivity per cm
2 is used (standardized to 100 cm2) and measured
with the LB 124 Scint. The result of this measurement is con-
verted into Bq/cm
2
using the formula
cps
A
K
Test
=
converted in Bq/cm
2
.
A
Test
= test radiation source activity in Bq/cm
2
,
or double surface emission rate
Calibration source requirements
For the calibration for beta radiation measurements, sources
meeting the requirements of the international standard ISO No.
8769 "Reference Sources for Calibration of Surface Contamina-
tion Monitors" are to be used. This standard prescribes that the
measured value has to be applied to the surface emission rate,
i.e. beta particles per second and per cm
2 being emitted from
the test source surface. The activity of the source in relation to
the surface in Bq/cm
2 then amounts to twice double of the sur-
face emission rate in s
-1 · cm-2.
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