SLIDE 19
Normalization of fallout activity to exposure rate. Beck recorded activity
per unit area per unit exposure rate factors for a number of particulate
gamma-emitting fission products and for a number of particulate activation
products and residual nuclear materials as the ground as a result of weapons
tests (Be80).
The exposure rates at one meter above the surface of a planar
source of unit area of Bikini Ash activity were calculated for each nuclide
based on the data of Beck (Be80) and nuclide composition of the ash.
By summing the product of each nuclide's exposure rate (relative to unit
activity per unit area) and fraction of total activity represented by each
nuclide in Bikini Ash, the exposure rate from aysiny 4
a 1Pe5 unit areal,
“1
activity,was estimated to be [.12 x 10
Ckg
“s
(5.8 x 10
Rh
mCi
km? ).
By inverting this sum and miltiplying by. the fraction of each
nuclide activity relative to the total Bikini Ash activity and the Rongelap
exposure rate on day 26, we estimated the beta activity of each nuclide per
unit area due to BRAVO fallout on the surface of Rongelap Island.
The estimates of mean unweathered activity per unit area due to BRAVO
fallout on Rongelap Island were extrapolated back to 0.5 days post
detonation.
The 0.5 day post detonation time was chosen by us as the point in
time at which the fallout at Rongelap Island had effectively ceased (Sh57).
First order linear kinetics for serially related nuclide species (Bal0, Sk75)
and decay schemes from Table of the Isotopes (Le/78) were used to calculate the
0.5 day activity from the day 26 activity.
The mean unweathered activity per
unit area for any short-lived precursor nuclide, not present on day 26 but on
the ground at the end of fallout at 0.5 days, was also calculated.
AREAL ACTIVITY RELATED TO EXPOSURE RATE
(Rho )Nuctide x
(Cim™)nuciide
(Ci
?)
ikint
Ash
(Ci) Nuctide
— {R h')iikini Ash
(Ci)pikim Ash
-
(Ci m™“)gitani Ash
i
uclide
“
Bikini x (Rh ")Meaaured x Nuctide_ = (Cim *) Nuclide
(Rh )piani Aah
(Ci)Bikini Ash
24