Appendix
r
CHANGES IN p DURING NONEQUILIBRIUM CONDITIONS
The rapid changes in the RaC/RaB atom ratio
(p) encountered in the chamber studies immediately after the addition of radon necessitated the
developmentof new tables relating the growth and
decay of radon daughteractivity collected during
20-min filtration periods to the radon concentration in the air. Such an approach was not required
for determinations of atmospheric radon, since
in that case it was assumed that the atmosphere
could be considered to be in or near a state of
dynamic equilibrium during periods of 20-min
duration.
Calculations of the collection and growth of
RaA, RaB, and RaC ona filter during a 20-min collection were made taking into account the changes
in RaA, RaB, and RaC occurring in the air prior to
and during filtration. These changes are a function
of the time during which the radon daughter products have been growing into equilibrium. The
decay of these activities on the filter following ter-
mination of collection and taking into account the
successive decay of members ofthe series is shown
in Table Al for collections made during periods of
growth of the radon mixture corresponding to
ages of 0-20 min, 40-60 min, 80-100 min, and
infinite age (secular equilibrium established). The
data used to construct working curves for determination of p and the radon concentration are
contained in Table A2.
14
Application of the information contained in
Tables Al and A2 to the results of the chamber
studies does increase the accuracy of radon
determinations during early states of growth
of the radon daughters; however, its affect
on the determination of g is not of great significance. A comparison of the results of the
small chamber run based both on the standard
procedure and on this more realistic procedure is shown in Table A3. Only during periods
of low p values are any substanual differences
noted in the derived radon concentrations. In
addition to the comparison of the experimen-
tal values of p and radon concentration for
the two procedures, the expected values are
also indicated; the experimental values of p
{by either procedure) and the expected values
are
in
good
agreement,
while the
measured
radon concentrations are about 50% low. This
latter result is attributed to a “wall effect” due
to the large surface-to-volume ratio and to the
mechanical mixing within the chamber making
the walls more accessible to impingement of
diffusing ions and unattached atoms. The sampling process itself removes 11.8% of the aerosol
and radon daughters with each collection, which
results in effectively 6% of the radon being in
a daughter-free, unmeasurable conditon during
any coliection.