Environmental Engineering Reference
In-Depth Information
TABLE 15.1
Relationship between the Function
F
(
θ
,
η
ba
;
η
ca
) and the Shift of
Equilibrium of Radon Decay Products
for Various Time of Inhalation
F
(
θ
,
η
ba
;
η
ca
)
10
4
erg·min
η
ba
;
η
ca
θ
= 3 h
θ
= 6 h
23.8
47.8
η
ba
= η
ca
40.8
81.4
η
ba
= η
ca
= 0
24.2
48.2
η
ba
= η
ca
= 0.8
24.5
49.0
η
ba
= η
ca
= 0.6
24.9
49.8
η
ba
= η
ca
= 0.5
25.3
50.7
η
ba
= η
ca
= 0.4
27.2
54.5
η
ba
= η
ca
= 0.2
30.0
60.0
η
ba
= η
ca
= 0.1
38.2
75.8
η
ba
= η
ca
= 0.01
of 0.25 for a duration of 3 h or more, the activity in the lungs will be about 0.02 μCi (740 Bq). This
activity can be measured by external counting with good statistical accuracy. To prove this, model
measurements were taken.
15.10.2.2
Correction for the Shift of Equilibrium of Radon
Progeny in the Air and in the Lungs
The laboratory measurement of radon decay product gamma activity in simulated lungs was con-
ducted using a calibrated sample of
226
Ra. The
226
Ra gamma spectrum is identical to the entire
gamma-spectrum of radon progeny. However, there is a difference in measurement of miners. In
the
226
Ra calibration source all radon decay products are in equilibrium, that is, their activities are
equal. The shift in equilibrium in the lungs will depend on the shift in equilibrium in the air and
this will change with time in the lungs.
This is especially important because the gamma-spectra of RaB and RaC are different, which
will result in the change of gamma-detection eficiency with the change of equilibrium both in the
air and in the lungs.
Let us denote
e
0
as the detection eficiency of RaB and RaC in equilibrium in the lungs or in the
standard source of
226
Ra,
e
b
the detection eficiency of RaB,
e
c
the detection eficiency of RaC,
e
the
detection eficiency in the case of the shift of equilibrium between RaB and RaC, and
k
2
(θ,
t
) =
e
0
/
e
the correction factor on inequality of detection.
(
N
+
N
)
b
,
0
c
,
0
e
=
0
2
A
0
where
N
b
,0
and
N
c
,0
are the count rates of RaB and RaC, respectively, from equilibrium RaB and RaC in
the lungs or in the standard source of
226
Ra in the phantom
A
0
is the activity in the equilibrium source
[
N
( , )
θ
t
+
+
N
( , )]
θ
t
b
c
e
=
[
A
( , )
θ
t
A
( , )]
θ
t
b
c
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