6
LOCKHART AND PATTERSON
In addition to the radioactivity measurements
1.00
described above, supplementary determinations
were madeat 5 to 6 hours and 17 to 18 hoursfol-
lowing collection to enable corrections to be
made for the small quantity of thoron daughter
products and fission products retained by the
filters.
30-mil AL ABSORBER
|
°
on
Chamber Studies
2
RoC/RoB ATOM RATIO (,)
OFS --
The effect of the residence time of radon in the
atmosphere on its experimentally determined con-
{O-mil AL ABSORBER
centration and on the measured p values was
5-mif Au ABSORBER
studied by the described technique following
release of a known quantity of radon gas (0.20 Ci)
into closed volumes of 35 m? and 0.31 m3. Con-
O.25;—
tinuous mixing was provided by low-speed fans.
Sampling was done at rates of 0.212 m*/min and
0.00196 m*/min in the two cases, resulting in the
NQ
ABSORBER
Oo
withdrawal of 11.5% and 11.8%, respectively, of
|
o25
Q50
|
O75
the particulate matter with each sample taken.
1.00
COUNTING RATE RATIO tet- 71/4) 4)
Fig. 6 — Effect of absorber thickness on the relationship
between the ratio of the counting rates at 1.11 and ¢61.7; and
the RaB/RaC atom ratio p
of longerlived activity (ThB+C and fission prodducts) to the initial count, which conditions ap-
proximate those actually encountered. The
statistical errors (a) corresponding to radon
concentrations of 100 to 4000 pCi/m3 andp values
of 0.735, 0.564, and 0.390 are presented in Fig. 8
for filter samples counted through 10-mil aluminum absorbers. It seems reasonable to expect this
method to permit radon concentrations to be
determined with a standard error of 5% or less
.?
eres PeaNABaiealas
pera
for most conditions where relatively high atmospheric concentrations (> 1000 pCi/m*) of
radon may develop.
Atmospheric Sampling
The filtered air was returned to the chamber.
Cigarette smoke was introduced imto the larger
chamber to supply a quantity of aerosol particles
to serve as nuclei for attachment of the shortlived radon daughters; a controlled quantity of
0.34 (dia) diocty! phthalate aerosol (DOP) was
used for this purpose in the second (glove-box)
experiment. The results of these two experiments
are discussed later in the next section.
RESULTS AND DISCUSSION
Radon concentration measurements in atmospheric samples made by the described technique
are summarized in Table 4 for the assumed conditions of continuous and of instantaneous emission
of radon from the soil and for secular equilibrium
in the atmosphere. The p values, also included in
Table 4, when compared with the secular equilibrium value of 0.735 given by Fig 3 suggest that
the radon/radon daughter relationship is cer-
tainly near secular equilibrium under the condi-
radioactivity were
tions prevailing at the sampling site. This reasonably close approach to equilibrium diminishes
above the ground. The sampling equipment was
contained in a box having louvered sides all
ple volume. The agreement between pairs of
Samples
of atmospheric
collected as described above on a roof 20 feet
around to permit unimpeded access of air; the
exhaust was directed upward and away from the
samplingsite.
in importance the assumption made as to the
mode of introduction of radon into the sam-
p values or radon concentrations obtained
from essentially duplicate determinations falls
within the range expected for measurements