BERTHOLD TECHNOLOGIES LB 3602, Руководство по эксплуатации

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LB 379
23
Isotope k
old
mCi h
m mrem
*
*
2
k
new
Mbq h
m mSv
*
*
2
241
Am
0.0158 0.0043
244Cm 0.0064 0.00175
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 241Am 244Cm
Water 40
12
Steel 0.9 0.05
Lead 0.125 --
The attenuation factor "s" can be calculated from the half-value thickness.
Example:
Activity:
3700 MBq (100 mCi)
241
Am
Shielding thickness: d = 5 mm steel
Distance: 0.2
m
s e e
d
HWS
  
0 693
0 693
5
0 9
47
. *
. *
,
Determine the dose rate in a distance of 0.6 m using the following formula:
mrem Sv
s a
t k a
D 846 . 0 46 . 8
47 * ) 2 . 0 (
1 * 0043 . 0 * 3700
*
* *
2 2
   

A = activity in MBq
k = radiation constant
t = time in hours
a = distance from the radiation source in m
s = attenuation factor
The result indicates that if you stay for one hour in a distance of 20 cm from the above
mentioned radioactive source, which is shielded by 5 mm steel, you will incorporate a dose
of 8.46
 Sv/h or 0.846 mrem/h. If you stay for a longer (or shorter) time in the vicinity of
the source, the dose increases (decreases) accordingly.
At
244
Cm, the gamma radiation is shielded almost completely by the housing wall of the
measuring path. In addition,
244
Cm emits neutrons. The dose rate at an activity of 3700
MBq (100 mCi) in a distance of 1 m is about 0.14 mSv/h and 0.014 mrem/h.