SLIDE 16
Granule fall time.
Information regarding granule fall time as a function of
granule size was derived from the deposition models which were reviewed by
Norment (No66).
Four models of fallout settling were presented as a function
of granule size and initial height (No66). Expressions for granule fall time
from various heights were derived by using the model results of Davies,
Hedman, Hastings or Ksanda as presented by Norment (No66).
The complexity of
each model varied, however, each investigator accounted for the aerodynamic
properties of irregularly shaped fallout granules.
The granule fall time
result versus granule size was best described by a power function in each
case.
Tsuzuki indicated the observed fallout arrival time,
granule size distribution for Bikini Ash (Ts55)}.
cessation time and
This data was used to model
a power function relationship which related granule size to granule fall time
specifically for BRAVO fallout as follows:
where
T= 79,5 p09524
T = granule fall time in hours post BRAVO,
D = granule size in micrometers.
It was assumed that the largest granules in the Bikini Ash fell upon arrival
and smallest granules fell upon cessation of fallout.
The times of arrival and cessation of fallout were observed at Rongelap
and Sifo Islands and at Rongerik Atoll.
estimate granule size at these locations.
The above equation was used to
The times of arrival and cessation
at Utirik were based on linear extrapolation of known arrival and cessation
times versus distance from detonation site. Thus, granule size at Utirik
could be estimatedusing the ahove equation.
BRAVO FALL TIME
Fall Timeof Size
At Median Activity
Location
Hours
5th Lucky Dragon
Rongelap Island
Sifo Island
Utirik Island
3.5
5.7
3.5
12
21