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incident on crew shield sides and rear. In ad-
dition, more detailed calculations of the TSF data
were made to estimate the fraction of scattered
radiation at the maximum altitude which is attribut-
able to ground scattering. There is evidence that
for many measurements it will be about 1%, and for
highly anisotropic shields such as the GE-ANP
R-1 it will be no more than about 5%. The con-
clusion is reached that the TSF towers are high
enough for experiments applicable to high-flying
ai rpl ones.
13. Lid Tank Shielding Facility
At the Lid Tank Shielding Facility (LTSF) the
effective neutron removal cross section for lithium
was determined as 1.01 5 0.04 barns. The meas-
made in a medium of oil behind a
solid slab of lithium, The experimentation with
helical air ducts was continued, and
measurements have now been made beyond an array
of thirty-five 3-in.-dia ducts both in a medium of
water and in a gamma shield medium of steel
Raschig rings and borated water. The presence of
the ducts in plain water increased the thermal-
neutron flux by a factor of 300; in the gamma shield
medium the ducts increased the flux by a factor of
3000. Preparations for the ref1 ector-moderated
reactor and shield mockup tests are being com-
pleted. It is now planned to use solid UO, as the
simulated fuel in the mockups. The UO, will be
mounted on a movable belt.
14. Bulk Shielding Facility
The Bulk Shielding Facility (BSF) was shut
down during much of the quarter for modifications
to the reactor pool. These modifications will permit
the use of demineralized water in the pool,
and thus they will eliminate corrosion of the
reactor fuel elements. Several BSF staff members
participated in a program to discover any shortperiod
isomeric gamma-ray transitions which might
bepresent in K39, Rb85, Rb87, and Zr90. Measurements
were made at the ORNL Graphite Reactor,
and no previously unknown short-period isomers
were found in K39, Rba5, or Rba7. Zirconium-90
yielded a 2.30 rt 0.03-Mev gamma ray with a halflife
of about 0.83 * 0.03 sec. This may be of
importance in design considerations for a circulating-fuel
reactor.
15. Tower Shielding Facility
Measurements made around the GE-ANP R-1
reactor shield in the TSF pool were compared with
similar measurements made earlier at the BSF.
The variation of the thermal-neutron intensity as
the altitudes of the mockup and TSF detector tank
were varied simultaneously was also measured.
The data indicated that ground-scattered neutrons
are still observable at the maximum altitude for
this particular reactor-shield combination. For
tests at the 195-ft altitude, lead was placed in the
rear of the detector tank to simulate the shielding
in the crew compartment, and the thermal-neutron
flux and gamma-ray dose rate distributions within
the tank were determined. This experiment was
interrupted for ci period of 2% weeks so that the
TSF could participate in an Air Force Project in
which a group of monkeys were exposed to massive
neutron radiation doses.
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