NRL REPORT 6374
ratio is quite different for the two conditions, as
1
!
4
1
\
4
°
shownin Fig. 2. The time parameter is removed
from consideration in Fig. 3 by comparing directly
the radon/RaB activity ratio with the RaC/RaB
i
{
\
\
ba
atom ratio (p), wherein smooth curves are obtained
\
2
\
E
which intercept the p axis at 0.735 for the equilib-
\
it
\
>
rium condition corresponding to infinite t:me.
\
c2= 30}-
3
,1
Interconversion of the single emission and continuous emission conditions can be obtained from
the plot in Fig. 4, where the relative radon concen-
uo
<
S
\
©
4
z
3
CONTINUOUS EMISSION
\
<
ity on a filter are shown as a function of the mea-
\
4
* 20
trations in the air required to give the same f activ-
OF RADON
\
sured p value obtaimable from the same filter.
\
SINGLE EMISSION \
OF RADON
“a
EXPERIMENTAL PROCEDURE
\
’ Air Sampling
L
0.1
—_L
0.2
J
0.3
0.4
05
06
RoC /RoB ATOM RATIO (Pp)
O77
08
Fig. 3 — Relationship between the radon/RaB activity ratio
and the RaC/RaB atom ratio (p) for the conditions of instantaneous and continuous emission of radon from the soil. These
curves are obtained by combining the data of Figs. 1 and 2.
Airborne particulate matter and associated
radioactivity have been effectively collected on
glass fiber filters having an exposed area of about
25 cm? through use of positive displacement
blowers (Roots-Connersville Models AF-24 or AF315) driven by 1-hp electric motors. Glass fiber
filters have essentially 100% retentivity for the
radon decay products at the air velocity employed
(2) and, moreover, are essentially surface collec-
tors; furthermore, no retention of the gaseous
a
nN
radon by filters has been detected. In this study
Gelman Type A filters were employed with the
fairly smooth, screen-imprinted back surface used
‘as the collecting surface to reduce theeffect ofselfabsorption of radiation by the filter.
The quantity of dust collected during the 20minute periods did not measurably affect the air
flow (between 0.42 and 0.52 m/min, depending on
the unit), though on occasion a definite imprint of
i
Oo
nm
RADON (CONTINUOUS) /RADON (INSTANTANEOUS)
the dust was apparent. The air sampling equip-
ment was calibrated against a rotameter-type flow
meter as a function of pressure drop across the
filter; flow was determined from pressure readings
|
a
SEE aE
10
taken at the start and the end of the run.
After the accurately timed 20-minute collection
Lo
OJ
i
0.2
l
0.3
Roac/RoB
|
l
|
o4
as
0.6
ATOM RATIO (,p)
period, the samples were transferred to other
07
08
Fig. 4 — Relative radon concentrations in the air under conditions of single and continuous radoninflux required to produce
identical quantities of radon daughter products. The values
plotted are obtained by direct comparison of the curves in
Fig. 3.
holders and counting was started 60 secondsfol-
lowing termination ofthe collection.
Radioactivity Measurements
All
radioactivity determinations were made
under conditions of standard geometry and