DATA REQUIREMENTS
To accomplish project objectives, initial gamma measurements were required versus distance from ground zero for each of three fractional-kiloton detonations. It was necessary that
the extent and magnitude of residual-gammafields be known so that data corrections could be
made. Residual-gamma readings were obtained from the early field surveys of Projects 2.10
and 2.12b and the Emmett devices of Project 2.9.
Total gamma doses were measured with film badges.
The film dosimetry used had an ac-
curacy of +20 percent, not considering residual radiation, station shielding, and neutron effects
TABLE 3
SENSITIVITY RANGES OF DOSIMETRY FILM
Packet Type
Emulsion
Range
number
r
DuPont 553
DuPont 553
502
§10
DuPont 553
606
Eastman Special Order
548-0 DC
on the film (Reference 9).
0.3 to §
3 to 50
25 to 2,500
2,500 to 50,000
It has been estimated that these effects, if uncorrected, could reduce
the accuracy of the film dosimetry to +50 percent (Reference 9).
Film emulsions are sensitive to capture- gamma photons and to thermal and fast neutrons.
The capture~gammaphotons are generated by thermal neutrons absorbed in the walls of the film-
protection container. Table 4 lists data from Reference 5 on the film sensitivity to neutrons.
The subject of neutron-capture photons generated in a steel shield has been treated in ReferTABLE 4
NEUTRON SENSITIVITY OF FILM
Packet
Tyr
Low-Energy (Gold)
Neutrons
Emulsion
number
n rep dose/r
606
3.441.8
28 +17
DuPont 553
502
3.2 41.7
2615
510
548-0 DC
2.3 41.4
4.721.9
19 +12
20 +12
For this steel, the capture photons can be estimated from the following equation:
-
2Knolt,
(-NEx__ Hx)
u-N=
Where:
*
DuPont 553
DuPont 553
Eastman Special Order
ence 10.
10 ~*(n/cm?)/r
High-Energy
Neutron Dose
P
(2)
generated dose, in roentgens
K = conversion factor from gamma flux to gamma dose, 2.39 x 10° r/(photon/cm*)
x = thickness of shield, cm
no = macroscopic activation cross section,per cm
pu = linear absorption coefficient, per cm
NZ
= macroscopic removal cross section, per cm
Th = incident thermal neutron flux, neutrons/cm?
The neutron effects all increase the indicated dose as read on the films; whereas absorption of
gamma rays by the shield decreases the indicated dose, resulting in someself-cancellation of
effects.
20