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animals or, in some cases, milk are taken from the same pasture where possible. An effort is
made to relate the Sr-90 content of babies from a large city to the Sr-90 content of the local
milk supply. Some of the questions raised by field observations, as well as problems of radiological effects, are incorporated into the rather large experimental program supported by the
Division of Biology and Medicine.
E. Information from weapons tests:
A great amount of information pertinent to GABRIEL is, of course, potentially available
in connection with weapons tests. Some of this is obtained for other purposes in the normal
course of events; other items become available only through projects specifically designed to
supply information for GABRIEL or for scientific interests which happen to be related.
In addition to studies of weapons effects made in support of the weapons development
program, it is feasible to include in the tests a number of programs supported for their general
While final approval of such programsis subject to the judgment of the
Certain methods of measurement, particularly in connection with Project SUNSHINE,are
of interest because of the high degree of specialization involved. Because of the amountof detail
involved in their description, they are presented as Appendix A.
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a
scientific interest.
Test Director that their inclusion is feasible, programs of interest to the Division of Biology and
Medicine are, to some extent, coordinated or instigated by screening committees sponsored by
the Division.
IV. SPECIAL METHODS
V. RECENT DATA PERTAINING TO PROJECT GABRIEL
In this section are discussed recent data which pertain to the steps of Project GABRIEL
as listed in Section II. Specific references are given only for material taken from formal reports.
A. Dependence of fallout on conditions of debris formation:
The ultimate time scale and spatial distribution of fallout from an atomic weapon detonation are greatly influenced by the conditions of debris formation: height of the burst
above the ground, the yield of the burst, and presumably also the soil conditions, The conclusions
listed below have been deduced * from detailed studies of a large number of American weapons
tests (almost exclusively Nevada series).
Airburst is defined to mean a shot in which the fireball does not touch the ground. Tower
shots (100-300 feet elevation) include those detonations in which a fraction less than one-half
of the fireball contacts the ground. Surface shots are those in which one-half or more of the
fireball contacts the ground. The percentages of fallout cited below are based on survey meter
readings inside a circle of 200 miles radius and gummed papercollections outside this circle.
While the gummed paper collections are here assumed to have an efficiency of 100%, the true
1. Initial distribution of radioactive material in the vertical:
a, Airburst—About 99%of all the activity remains in the mushroom or toroidal cloud in
a finely divided form, and some 1% is left in the wake, extending from the burst point up to the
mushroom. The fallout curtain of slowly descending particles of intermediate size develops
after the cloud stabilizes, but this appears to constitute even less than the wake and is usually
barely detectable in the case of an airburst.
b. Tower shot—Most of the material is taken up with the mushroom, but the settling of
the entrained dust and sand apparently brings some of the debris back down into the stem and
results in some radioactivity at all altitudes. The fraction of the total radioactivity removed
from the mushroom in this way is in the order of 20% to 50%.
Footnote references on pp. 42-43.
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value is certainly lower, as discussed later.