gp” activity on the planchet increases linearly with the number of grams burned on the planchet.
Therefore, there is no need to burn the whole sample if enough counts per minute are reached
to enjoy good statistics before burning the fuli 800 grams.
2.3.2 Neutron Film. Nuclear track films are photographic films especially prepared to show
proton tracks in the emulsion. The protons are evolved by two mechanisms; the first being the
N'4(n, p) C!4 reaction caused by thermal neutrons and the second being hydrogen recoils caused
Soe ae
by fast neutrons. Protons travelling through the thick emulsion leave dense tracks that canbe counted under a microscope. The films used were the Kodak personal neutron-monitoring films,
Types Aand B. The Type A film was known for manyyears as Kodak nuclear-track dental-size
film, Type NTA. The Type B badge contains two pieces of film and two sheets of aluminum in
.
ih
*
of
nt
ve
te
f
\
pon
f*.
Figure 2.13 Fallout detector{MG-3), showing detector,
indicating, and recording units.
addition to the packaging material. Aluminum shields and cellulose radiators make the nucleartrack population a measure of dose, independent of energy. The films were returned to AFSWC
for processing and counting of the proton tracks.
Figure 2.16 shows the calibration curves,
derived from exposing both sulfur and Types A and B films at the Los Alamos Godiva.
2.3.3 RTF Dosimeters. Resonance-threshold foil (RTF) personnel neutron dosimeters were
exposed at six locations as indicated in Table 2.1 and Figure 2.3. The dosimeter case was 2-S
aluminum, 0.102-inch thick. The aluminum case housed three sets of indium foils. Each set of
foils was in a package of three 0.003-inch-thick disks, approximately 0.625 inch in diameter.
One set of the indium foils was unshielded, and was activated by neutrons up to 0.1 kev. The
second group of foils was covered with 0.010-inch-thick cadmium disks. Only neutrons with an
energy greater than the cadmium cutoff (0.5 ev for the thickness used) could activate the indium.
25