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 gammaradiation exposure rates and local
surface deposition of related radionuclides resulting from selected U.S. Pacific events.
Introduction
In the past, we have calculated the normalized external gammaradiation exposurerates that
resulted from local fallout from the Nevada Test
Table 1.
the reconstruction of radiation doses downwind
Mike
Site (NTS).' These calculations have been used in
of NTS. More recently, we were asked to make
similar calculations to assist in the reconstruction
of doses to personnelparticipating in nuclear tests
in the Pacific. This report contains the results of
these calculations that we made and that were
used by the Nuclear Test Personnel Reviewof the
Date, placement, and yield of se-
lected U.S. Pacific events.
Event
Bravo
Romeo
Yankee
Zuni
Tewa
Date
Oct. 31, 1952
Feb. 28, 1954
Mar. 26, 1954
May 4, 1954
May27, 1956
July 20, 1956
Placement
Yield (MT)
Surface
10.4
Surtace
Barge
Barge
Surface
13.5
3.5
Barge
15.0
11.0
5.0
Defense Nuclear Agencv and its contractors.
The selected U.S. Pacific events” are listed in
Table 1.
Results
Results of the calculationsof relative external
gammaradiation 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
decav times: 10 from 1 to 21 h, 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 normalhzed to
i mR/h, 1 m above the surface, 12 h after the
event; the associated values of uCi/m* for each
the concentration of fallout varies exponentially
with soil depth, Z, according to the relation
C = C,e~*4. He defines relaxation length as 1/a.
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 for
using Beck's values? of (mR/h)/(uCi/m?) for a relaxation length of 0.16 g/cm?. According to Beck,
ternal gamma-ray exposure rates and associated
radionuclide; and the total uwCi/m-.
Surface roughness effects are simulated by
debris with 0.5 and 0.1 of the refractorv elements
present.
Each Appendix contains three sets of 11
pagesof 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 ex-
values of total microcuries per square meter at 30