the atmosphere and in the weapon’s high explosives.
These photons have high energies (5 to
10 Mev) and account for almost all the dose received from a few milliseconds to a quarter of
a second.
For high-neutron-flux fission weapons ( < 20 kt), this dose accounts for 50 percent
of the total initial gamma dose at 1,000 yards and 90 percentat 3,000 yards.
3.
Fission-product gamma rays emitted from the fireball and cloud.
These rays have a
mean energy of about 1 Mev and account for the dose received after the first quarter second.
This dose drops off rapidly as the fission products decay and the fireball rises.
Reference 7 contains a collation of initial gamma-dose data from many previous operations.
By plotting experimental values of dose-per-unit yield times distance squared versus distance
for surface bursts of low- and intermediate-yield weapons, it was found that the straight line
of best fit is described by the following equation.
2
oe
eff
Where:
D =
R
W
hose
p
=
=
“=
=
= 1.93 x 10% e? R/324
(a)
initial gamma dose, roentgens
distance from detonation, yards
yield, kt
effective hydrodynamic scaling factor = 1 for subkiloton bursts
relative air density
The residual nuclear radiation is defined as that emitted after 1 minute following the detonation. This radiation arises from deposited bomb residues (fission products, unfissioned uranium and plutonium, neutron-activated bomb materials) and from activity induced by neutrons
captured in various elements present in the earth or in substances in the vicinity of the detona-~
tion. In the case of an air burst, the fission products and bomb residues are dispersed widely
and usually do not produce a military problem. However, the induced activity in the soil near
ground zero may constitute a military problem for early operations in this area.
Induced gamma activity in soil results when neutrons are captured by nuclei of certain soil
elements. The resulting products are radioactive isotopes of the original absorbing elements
and can be expected to be unstable.
These decay to stable isotopes, usually with the emission
of a gamma ray. In the case of most soils, the significant elemental constituents that become
activated and cause the induced gamma field are aluminum, manganese, and sodium (with half
lives of 2.3 minutes, 2.6 hours, and 15 hours, respectively). Project 2.12c investigated soilinduced activity, and a detailed discussion of this phenomenon can be found in the reportof that
project (Reference 8).
OPERATIONS
Project 2.9 participated in Shots Quince and Fig at Site Yvonne, Eniwetok Proving Ground
(EPG). Project 2.12b participated in Shots Hamilton and Humboldt at Frenchman Flat and Area
3, respectively, Nevada Test Site (NTS). Table 1 lists some of the characteristics and conditions
of detonation of these shots.
EPG Operations. Stations were placed as follows: (1) thirty-six film-badge stake stations
on land, (2) four Emmett devices on land, (3) eight film-badge stations along the Project 2.4a
west neutron line on land and water, and (4) seven film-badgestations aloft at Project 2.4a sta-
tions, hung vertically from the Project 2.11 balloon.
The location of the film-badge stations on land, water, and the balloon are shown in Figure
1.
Station distances and azimuths for all stations are tabulated in Table 2.
The station array
-is far from ideal because of the limited land mass and obstructions, but is the best compromise
of available locations with line of sight to ground zero.
The project participated in Shots Quince and Fig with identical instrumentation being used
for both events.
The dosimeter film badges were installed several days before the shot and re-
covered at approximately H+24 hours.
Film badges were calibrated immediately following
10