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i0 60 70 80 90 100 110 120 I30 140 150 160 170
2, DISTANCE FROM SOURCE Icm)
Fig. 13.2. Thermal-Neutron Flux in Oil With
and Without Bismuth Slab to Suppress Photoneutron
Production.
measurements were made in the oil behind the
29.1-cm thickness of the lithium (Fig. 13.3). From
these measurements the value of 1.01 k 0.04 barns
was calculated for the removal cross section of
lithium by the procedure presented below.
All previous removal-cross-section measurements
were made in water. In order to verify that a
correction to a water medium would not be neces-
y for these measurement^,^ thermal-neutron
asurements were also made in oil behind a
material which had a uR predetermined in water.
The definition of a removal cross section has been
given as a parameter characterizing the attenuation
of fission neutrons by materials either mixed with
hydrogen or followed by a hydrogenous layer; see H.
Goldstein and R. Aronson, “Effective Removal Cross
Sections-Theory,” abstracted in Symposium on Fission
Physics and Classified Nuclear Physics for Reactors
13-15, 1954, ORNL CF-54-10-11,
2- ._
L
-..
‘x..
Fig. 13.3. Thermal-Neutron Flux Beyond Lithi-
um in Oil.
The material chosen was bismuth, and the measure-
ments in oil behind a 22.9-cm-thick slab *are
plotted in Fig. 13.4. From these measurements
a value of aR = 3.48 barns was calculated, which
can be compared with a value of 3.49 9 0.35 barns
previously determined for bismuth from measure-
ments in water.4 Gamma-ray dose measurements
made throughout the experiment are plotted in
Fig. 13.5.
The removal cross section of lithium was calcu-
lated by a method suggested by Bli~ard:~
4C. L. Storrs, G. T. Chapmon, and E. P. Blizarcf:
“Effective Remova I Cross Sections -Experiments,
ORNL CF-54-10-11, op. cit., p 101 (Oct. 8, 1954).
5E. P. Blizard, Procedure for Obtaining Effective
Removal Cross Sections from Lid Tank Data, ORNL
CF-54-6-164 (June 22, 1954).
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