-
Results of Calculations
of External Gamma
Radiation Exposure Rates
from Local Fallout and the
Related Radionuclide
Compositions of Selected
U.S. Pacific Events
Abstract
This report presents data on calculated gamma radiation exposure rates and local
surface deposition of related radionuclides resulting from selected U.S. Pacific events.
Introduction
In the past, wehave calculated the normal-
ized external gamma radiation exposure rates that
resulted from local fallout from the Nevada Test
Site (NTS).' These calculations have been used in
Table 1. Date, placement, and yield of selected U.S. Pacific events.
Event
Date
Placement
the reconstruction of radiation doses downwind
of NTS. More recently, we were asked to make
Mike
Bravo
Oct. 31, 1952
Feb. 28, 1954
Surface
Surface
of doses to personnel participating in nuclear tests
Yankee
May 4, 1954
Barge
similar calculations to assist in the reconstruction
in the Pacific. This report contains the results of
these calculations that we made and that were
used by the Nuclear Test Personnel Review of the
Defense Nuclear Agency and its contractors.
Romeo
Zuni
Tewa
Mar.26, 1954
Barge
May 27, 1956
Surface
July 20, 1956
Barge
Yield (MT)
10.4
15.0
11.0
13.5
3.5
5.0
The selected U.S. Pacific events’ are listed in
Table 1.
Results
Results of the calculations of relative external
gamma radiation exposure rate and related radionuclide ground deposition are given in the Appendices. These calculations are described in detail in Ref. 3. The output of the calculation has 30
decay times: 10 from 1 to 21h, 10 from 1 to 300 d,
and 10 from 1 to 50 y. For each of these times and
for zero time, there are values of the external
gamma radiation exposure rate normalized to
1 mR/h, 1 m above the surface, 12 h after the
event; the associated values of uCi/m* for each
radionuclide; and the total wCi/m?,
Surface roughness effects are simulated by
using Beck’s values’ of (mR/h)/(uCi/m?) for a re-
laxation length of 0.16 g/cm*. According to Beck,
the concentration of fallout varies exponentially
with soil depth, Z, according to the relation
C = C,e~"*. He defines relaxation length as 1/q.
Fractionation effects were simulated by the
removal of a fraction of the refractory nuclides
from the calculation. Calculations for each event
were performed for unfractionated debris and tor
debris with 0.5 and 0.1 of the refractory elements
present.
Each Appendix contains three sets of 11
pages of calculated results relating to one event in
Table 1. Each set of 11 pages is marked Page 2
through Page 12. Page 2 of each set gives the external gamma-ray exposure rates and associated
values of total microcuries per square meter at 30