A(h, f) and I are measured at the same time.
When A(h, f) is known, I may be calculated
for any point once the contributing altitudes and fall rates are obtained from a particular
hodograph and the cloud dimensions.
Also, estimates of the amountof fallout activity collected by an air sampler operating at
a given location in the fallout field may be made from the fallout model for any particular
wind situation. Let C(t) be the activity density in the air at a location in the falloutfield,
and B be the air sampling rate. The amountof fallout activity collected from air sampled
during the time of fallout is then u.
u
B {
t=T
=0
Therefore,
C (t)dt
(1.2)
Where: t = time measured from the start of fallout to its cessation
att=T
During fallout arrival, activity density in air near the surface is caused bya slice of
cloud dh thick, which has fallen from h and which contains particulate matter covering a
sma)]] range of fall rates from f to f + df.
The time for this thin slice to fall dh past a point near the surface is
at = 22
f
(1.3)
During this time, the activity density will be the same as that which existed in the cloud at
altitude h on fall rates from f to f+ df, provided cloud dimensions do not change appreciably with time. Therefore,
u=Bffa (fh,
Ddfdh
sa
(1.4)
comparison of Equations 1.1 and 1.4 reveals an important relationship between I and u,
which depends on the fall rate of the contaminating particle. If the range of fall rates that
may contribute to a given point is small compared to f, the mean fall rate contributing,
then
T=Bl
|
u
TABLE 1.1
(1.5)
POSSEBLE CLOUD DIMENSIONS
Cloud height
Puff diameter
Stem diameter
Ratio of stem to puff height
14
5,500 feet
2,000 feet
1,000 feet
4