ORNL-1816 - the Molten Salt Energy Technologies Web Site

200 ft are relatively free from a background of
ground-scattered neutrons.
In each experiment the neutron flux reaching a
BF, detector placed inside the detector tank and
near a side wall was measured as the altitudes of
the source and the detector were varied simul-
taneously from the ground to 200 ft. The only
major difference between the two experiments was
the shielding placed around the TSF reactor. In
the first case the reactor was placed in the reactor
tank at a distance (p) of 45 cm from the tank wall
and a reactor angle (e) of 330 deg from the source-
detector axis;14 in the sec:ond case the reactor
was placed in a mockup of the GE-ANP 8-1 shield
design (see “TSF Experiment with the Mockup of
the GE-ANP R-1 Shield Design,” in Sec. 15).
In order to estimate the actual ground-scattered
contribution at the 200-ft altitude, attempts were
made to analytically separate the experimental
measurements into their air- and ground-scattered
components. A calculation16 of the number of
neutrons singly scattered into a point isotropic
detector as a function of the solid angle in which
they had left the source had been made previously
PERIOD ENDING DECEMBER 70, 7954
Fig. 12.9. Angular Distribution of Fast Nieutrons
for the case of infinite height. Also, a calc~lation~~ Emitted from GE-ANP R-1 Shield Mockup.
of the number of air-scattered neutrons lost because
of the presence of the ground and the number of
ground-scattered neutrons reaching the detector as
a function of source solid angle and altitude had
been made, All three calculations assumed single
isotropic scattering, air attenuation, and a separation
distance of 64 ft.I8
The integration over the source solid angle to
obtain curves of air and ground scattering as a
function of altitude was weighted in each case by
the anaular d -of neutrons emitted from
ata, it was assum e ground-
18The measurements with the GE-ANP R-1 mockup
were actually for a 70.8-ft separation distance.
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8, ANGLE WITH RESPECT TO REACTOR-CREW SHIELD AXIS (degl
scattered contribution to the data at 200 ft was
negligible, and the single air-scattering curve as a
function of altitude was normalized at this point.
This normalized curve was then used to subtract
the air-scattered contribution from the experimental
measurements at lower altitudes, and thus (1 series
of experimental ground-scattering points was ob-
tained. A fit of the calculated ground-scattering
curve through these points gave an estimate of the
ground-scattered contribution to the experimental
data at the high altitude. The air-scattering was
then renormal ized, with this ground-scattered con-
tribution taken into account. This method of
iteration, of course, quickly converges.
The analysis (Fig, 12.10) for the differential
typeof experiment resulted in an estimate of 1% for
_.
the ground-scattered co
water-filled reactor tank. The estimate obtained
19H. E. Hungerford, Bulk Shteldzng Facility Tests on
the GE-ANP R-1 Divided Shield Mockup, ORNL CF-54-
8-94 (to be issued); see also ANP Quar. Prog. Rep.
Mar. IO, 1954, ORNL-1692, p 124.
3
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