ORNL-1771 - Oak Ridge National Laboratory

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PERiOD ENDING SEPTEMBER 70, 1954
14. TOWER WELDING F A ~ ~ ~ ~ ~ Y
C. E. Clifford
T. V. Blosser J. L. Hull
L. 6. Holland F, N. Watson
Physics Division
Q. L. Gilliland, General Electric Company
M. F. Valerino, National Advisory Committee for Aeronautics
J. Van Hoomissen, Boeing Airplane Company
The Tower Shielding Facility (TSF) experimental
program has, thus far, included measurements of
ground- and air-scattered fast neutrons and the
development of a new procedure for the determi-
nation of the power of the reactor. Tests on the
GE-ANP R-1 divided-shield mockup have been
started.
FAST-NEUTRON GROUND AND AIR
SCATTERING MEASUREMENTS
T. V. Blosser
D. L. Gilliland
J. Van Hoomissen
F. N. Watson
The performance of neutron and gamma-ray air
scattering experiments that are free from an ex-
cessive background of ground-scattered radi ation
is a primary objective of the TSF. Therefore,
measurements of the scattered fast neutrons as
a function of reactor-detector altitude were neces-
sary to determine the contribution of ground-
scattered radiation to the total flux, particularly
at the maximum altitude. These measurements will
help to indicate the magnitude of the yround-
scattered neutron background to be expected in
future differential experiments, and they will aid
in an understanding of the variation of ground and
air scattering as the ground is approached.
Measurements of the thermal -neutron distribution
were taken in the detector tank, which is es-
sentially a 5-ft cube of water and which was, for
these experiments, situated 64 ft from the reactor
tank. The reactor wos placed at an angle 8 of
330 dey from the d axis (Fig. 14.1), and a BF,
counter was moved along a lrne normal to and near
the right side of the detector tank. In this region,
contributions from other faces of the tank were
negligible; thus the neutrons detected by the
counter were the air- or ground-scattered fast
neutrons which entered the side wall and were
thermalized in the water near the detector. The
reactor and detector tank altitudes were varied
simultaneously, in discrete steps, from 0 to 195 ft-
k composite plot of the measurements (Fig. 14.2)
indicated only small difterences in slope but ap-
preciable differences in magnitude between the
curves for the various altitudes. A plot of the
flux vs the altitude (Fig. 14.3) showed o pro-
nounced peak in the region between the 15- and
20-ft altitudes, which indicated the importance of
ground-scattered neutrons in this region, It should
be noted that the reading at zero altitude was
obtained with the reactor half-irnmersed in the
ground pooi, the upper half being shielded as
before; so essentially half of the source was
occluded, as WQS hQlf of the scattering medium.
Thus the air-scattered neutrons should be no more
than half of the valwe at full altitude and no less
than one quarter. Because the intensities at the
150- and 195-ft altitudes were the same, it was
concluded that the ground-scattered contribution
at these altitudes was small.
In a preliminary analysis of the data, it %as
estimated that this contribution was 2 to 5% of
the total scattered neutrons, While the detailed
calculntians of ground and air scattering being
undertaken in connection with this investigation
are not yet completed, a preliminary comparison
of the data with calculations carried OLJ~ at the
Boeing Airplane Company for Q not too dissimilar
situatforr has been made. The qualitative agree-
ment is very good, although the peak in the total
flux, as measured, seenis to be at a lower altitude,
A report on this experiment is being prepared.’
C A REACTOR BOWER ~ ~
DE KE ~ ~ ~ ~ ~
D. I_. Giililand L. 13. Holland
J. I_, Hull
A grocedtire has been developed and tested for
CI calorimetric determination of the power of the
175