INTERNATIONAL SYMPOSIUM ON TRACE GASES AND RADIOACTIVITY
‘re I this is sufficient for Rn and
1 decay products, if 2, = 3 x
10°
‘ case. However, the concentratio
n
ved Rn™ decay products is still
not
this altitude. For this reason
the
is, in general, extended to the
rekm <z < «© by putting
K =
10°
———-
10°
10°
a
2
10°
x 10‘ cm?/see for z => 2,.
We then
z,) = —8,. Starting with an
arbi-
‘alue, o(z,) = c, and
the initial
= —B,c, we computed the valu
es
1) forjon — I, ++,
0, succes-
undary condition at Z was
then
Itiplication with a suitable fact
or.
ating-point overflow—the
g; inS z decreases—it was sufficie
nt to
ently small in most cases.
The
(Siemens model 2002)
admits
10™ and 10" for variable
point
‘o Include theless favorable
cases
z, instead of with Zn for
which
5
} 10"
a
10
D6
re 10
|:
20
aM
10 E
oO
5
7
10
2
12
m
10
5
10°
-l
10"
a
100} a,8; > 100
1
iS suggested by the exponential]
solutions (¢ a. 10°). In
fact
he boundary conditions atz
=
‘o are negligible if p < n,
© error caused by replacing
the
‘tep function the computation
ome cases with a larger number
atlons were negligible.
RESULTS AND CoMPARISO
N
XPERIMENTAL Data
shows the Rn™ profiles whi
ch
th the typical K profiles giv
en
are standardized to a mea
n
1 atom/cm! sec. Exhala
tion
everal places having nor
mal
he soil material indica
te an
rate of 0.2 to 1.5 ato
ms/em?
1 rather good agreement
with
1 atom/em? see which
was
ally by Israel [1958, 196
2]
ransport of Rn™ in the sur
Tound. It follows that
the
files in Figure 2 should
be
with the results of mea
mental areas having
normal
3803
\
Orem
10cm
Im
10m
100m
Tkm
km 30km
Altitude
Kite. 2.
Vertical profiles of radon (Rn**), calculated with Era = 1 Rn atom/cm® see for the
K profiles JVWN, WNN, NWN, NNN, and SSN.
Figure 2 indicates that the Rn*” concentration
in the boundarylayer, being strongly dependent
on the mixing rate, varies by about a factor of 100
from a minimum value of about 0.3 x 107° ¢/m*
for strong turbulence (case SSN} to a maxi-
mum value of about 30 x 10° c/m? for a strong
inversion (case JIVN). This range corresponds
rather well to the observed fluctuations of the
concentration near ground level. Compared with
this variation, the influence of short time
changes of the Rn™ exhalation from the
#round is negligible. The theory indicates that
& mean concentration of about 10° ¢/m* should
be. expected near ground level, in agreement
with the mean values of most measurements at
continental locations [Hultguist, 1956; Israel,
1962],
Figure 2 also shows the interesting result
tht variations of turbulence have only a little
influence on the concentration in the region
from 0.5 to 2 km, because in this region the
ay
are intersecting. For the rather extreme cases
which we have discussed, the concentration in
this region varies only by about a factor of 5
as compared with a factor of 100 in the air near
the earth’s surface.
The radioactive decay of Rn™ (t. = 3.8 d)
leads to a monotonic decrease of the concentration with inereasing altitude. According to the
theory, a significant concentration gradient
should be expected only in the boundary laver
and for very weak turbulence, ie., especially
during strong inversion periods at night (case
IWN in Figure 2). This theoretical conclusion
can be checked by the observations of Moses
et al. [1960]. Figure 3 shows observed Rn™
and temperature profiles at the end of nightly
periods which had high stabilitv and rather
constant wind velocity. The observed profiles
during strong inversions correspond rather well
to the calculated profile for this case (profile
TWN).
Beyond the ground laver over continental
areas we made only a few series of Rn™ measurements which allow a comparison with the