04/03
347
LB
444
88
To calculate the dose rate generated by a source, you need to know the gamma radiation
constant (k), in order to take into account the different energies of the various isotopes.
The following table lists the constants for the radioactive sources most frequently used in
industrial applications:
Isotope
k
old
mrem m
h mCi
*
*
2
k
new
µ
Sv m
h Mbq
*
*
2
Co-60 1.35
0.365
Cs-137 0.35
0.095
3. Half-value
Layer
Half-value layer (HVL) or half-value thickness (HVT) specifies the material thickness nec-
essary to reduce the intensity of a certain type of radiation to half its original value. The
following table lists the half-value thickness of some materials:
Half-value thickness layer in mm
Isotope
Material Co-60
Cs-137
Water 157
110
Concrete 68 47
Steel 20
14
Lead 14
7
The attenuation factor “s” can be calculated from the half-value thickness.
Example:
Activity:
9250 MBq (250 mCi) 137-Cs
Shielding thickness:
d = 50 mm lead
Distance: 0.6
m
Determine the dose rate in a distance of 0.6 m using the following formula:
mrem
1.73
Sv
17.3
141.2
*
(0.6)
1
*
0.095
*
9250
s
*
a
t
*
k
*
a
D
2
2
=
=
=
=
µ
A
= activity in MBq
k =
radiation
constant
t
= time in h
a
= distance from radioactive source in m
s =
attenuation
factor
Summary of Contents for LB 444
Page 1: ...Density Meter LB 444 Id No 32816BA2 Rev No 04 22 04 03 ...
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Page 9: ...04 03 347 LB 444 VII ...
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Page 109: ...04 03 347 LB 444 99 13 4 Mounting Device 90 for Pipe Diameter 21 3 76 1 mm ...
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Page 117: ...04 03 347 LB 444 1 14 Ex Certificates for Evaluation Unit ...
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Page 120: ...04 03 347 LB 444 4 15 Ex Certificate for the Detectors ...
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