ORNL-1771 - Oak Ridge National Laboratory

ANP QUARTERLY PROGRESS REPORJ
50-cC ION
41%
ORNL-LR-DWG 2657
Fig. 13A, Gamma-Ray Dose Measurements
hind AGHT Graphite.
1-ft graphite thickness between the reactor face
and the end of the spectrometer collimator is shown
in Fig. 13,5. The spectrum measured with the end
of the collimator against the reactor face is also
s t1own.
Removal cross sections have been calculated for
each thickness of graphite by use of a method
suggested by E. P. Blizard.4 The resulting cross
sections are 0.82 barn/atom for the 1-ft slab,
0.84 badatom for the 2-ft slab, and 0.80 barn/atom
for the 3-ft slab. These removal cross sections are
in goad agreement with measurements made on
graphite at the LTSF.
REACTOR AIR GLOW
R. G. Cochraii T. A. Love
K. M. Henry F. C. Maienschein
R. W. Peelle
Attempts to theoretically determine the amount of
visible light which may surround a nuclear-powered
airplane in flight have resulted in widely differing
~alues.~'~ Therefore an experiment was performed
at the BSF to provide an experimental basis for
future estimates.
The end of an air-filled aluminum periscope tube
was placed at the reactor face, and the amount of
light produced in the tube was measured by a
photomultiplier with spectral response similar
to that of the average human eye. Other relative
measurements were token with a photomultiplier
which was sensitive chiefly in the blue and near-
ultraviolet range. The latter measurements are
plotted in Fig. 13.6 as functions of the air pressure
in the tube. Measurements with argon in the tube
demonstrate that nei ther the approximate amount of
light produced nor the exact spectrum emitted is
strongly dependent on the atomic number of the
gas. It is also interesting to note that the light
production in a given volume of air appears to have
a maximum at a pressure corresponding to an
altitude of about 30,000 ft.
It is demonstrated in Figs. 13.7 and 13.8 that
the air glow is largely caused by gamma radiation
rather than by neutrons. Figure 13.7 shows the
decay of the light plotted along with the decay of
the reactor gamma ion chamber current just after
reactor shutdown. The attenuation by water of
the radiation which produces the air glow is shown
in Fig. 13.8. This attenuation rather closely
follows that of gamma rays.
The photomultiplier was used to compare the
quantity of light given off in the air-glow tube with
that from a small tungsten lamp mounted at the
reactor end of the ti~be, This comparison showed
that 7.2 x lom5 lumen was given off by the glow
for c1 reactor power of 100 kw and atmospheric
pressure. Presumably, the amount of light should
be proportional to the integral of the gamma-ray
dose rate over the volume of the air in the measuring
tube.
10
This integral was estimated to be 1.1 x 10
(r.cm3)/hr. Therefore the effective light production
per unit V O ~ Lof J ~ air ~ is
L : 6.5 x (Iumen/cm3)/(r/hr).
If it is assumed that all the light is given off at
4E. P. Blizard, Procedure /or Obtaining E//ective
Rernoval Cross Tertzons froin Lid Tank Data, QRNL
CF-54-6-164 (June 22, 195.1)-
5T. A. Welton as quoted by C, E. Moore, Visual
Detectability o/ Azrcralt at Night, LP.C-15, p 24 (Aug.
14, 1953).
6J. Ea Faulkner,_Vrsible 1.1ght Produced in Air Around
Reactors, ORNL Lt -54-5-99 (to be issued).