Also built into the unit was a standardizing source.
gas (Kr®5), The source was hermetically sealed.
The radioactive material was krypton
It hada thin, stainless-steel window through
which beta radiation reached the ion chamber when the source control was turned on.
The recorder unit was an Esterline-Angus strip type with a spring-operated paper drive.
chart drive was capable of speeds ranging from 12 in/min to ¥, in/hr.
The
The recorder charts of
both MG-3 units were operated at a speed of ¥, in/min; each chart was 100 feet long.
The two
instruments were located 650 and 30 yards from ground zero, the former to measurefallout and
the latter to measure the rate of decay of activity produced in the soil by the neutrons escaping
from the device. The steel case of the close-in detector was surrounded by 6 inches of boric
acid and 12 inches of paraffin to minimize activation of the case itself. It was placed in a hole
553 FILM PACKET
pso2
+0 SiO
a
DENSITY , UNITS
a
/
27
uw
7
V 7ona.
~
7
o
{
ot pty
1
tot pelt it
o
f tg
iiyl
ROENTGENS ,Co
@ 108
{Yo
td
itty
2
it
1
0
Figure 2.12 Calibration curves for NBS dosimeter film.
4 feet square and 4 feet deep and covered by a thickness of 4-by-4 lumber and two layers of
sandbags (see Figure 2.15). It was connected to the power supply and recorder by 1,000 feet of
cable buried 6 inches under the surface.
,
‘
2.3 NEUTRON MEASURING DEVICES
Neutron flux was measured with sulfur bags, sulfur planchets, nuclear-traca cuulsions, and
neutron dosimeters (Table 2.1).
2.3.1 Sulfur.
Common S* when irradiated with neutrons above 2.5 Mev energy, undergoes an
(n, p) reaction to become P**,
a 87 emitter.
When the 8~ emission is counted, the flux of neutrons
with energies above 2.5 Mev can be“calculated, and consequently, the neutron dose can be esti-
mated (see Section.1.2.2).
:
Sulfur pellets and planchets have often been used in this manner. One limitation of this method
is that the pellets and planchets cannot measure doses below approximately 1 rem with conven-
tional counting equipment.
To measure an extremely low flux of neutrons above 2.5 Mev energy, large samples of sulfur
(800 grams in this case) can be exposed and the activity concentrated by burning the whole sample
in one planchet. Nearly all the P®* remains in the planchet, while nearly all the S** burns.
24
The