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ANP PRO.JECT QUARTERLY PROGRESS REPORT
45
40
35
30
10
5
0
DISTANCE FROM REACTOR MID-PLANE (in.)
Fig. 5. 4. Indium-Foil Activation Along Axis of Reactor.
resultant act,ivities collected on the
foils are a measure of the fission
rate caused by the higher energy
neutrons. From these and the data
from the preceding experiment, it is
observed that about 70% ofthe fissions
are produced by thermal neutrons..
Two, adjacent, 10-mil-thick uranium
pieces were replaced by ten pieces
that were each 2 m i l s thick and
separated by aluminum foils. From the
observed distribution of activity
across this composite fuel element,
the self-shielding of the 20-mil-thick
uranium is found to be 34%, that is,
only 66% of the uranium is effective,
This figure of 66% is in satisfactory
52
agreement with afigure of 63% computed
from the multigroup data. Of course,
the orientation of the disks, parallel
to the neutron current from the re-
flector, and the nonuniform power
distri.bution make the theoretical
calculation difficult and somewhat
uncertain,
ARE CRITICAL ASSEMBLY
D. Scott C. R. Mills
ANP Division
J. F. Ellis D. V. P. Williams
Physics Division
The preliminary assemLly of the ARE,
which has been described in previous