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"fast" neutron in a graphite reactor and that there
are two traps per displacement. The question is
whether it is possible to calculate the number of
displacements on the basis of a reasonable
graphite reactor spectrum and to achieve approxi-
mate agreement with the experimental result of
2.5 displacements per fast neutron. (A fast neutron
is defined25 by Cleland et al. to be a neutron with
energy greater than that required to displace an
atom.)
For the calculation the method of Kinchin and
Pease" was modified to include a spectrum which
is the sum of 1/E distributions extending to each
element of a fission spectrum.26 The agreement
between the calculation and the experimental re-
sult was within a factor of 4. The spectrum and
the variafion of displacements with energy are
then roughly correct, or at least there are com-
pensating errors.
In order to test the variation with neutron energy
alone, it is planned to use neutron sources of
known energy. The flux from these sources is
reduced by factors of lo3 to lo5 from graphite
reactor fluxes, but the sensitivity of pure germanium
allows for experiments even at these low levels.
Two sources will be used: a uranium converter
plate in a thermal column and an antimony-beryl-
lium source. The converter plate gives a pure
fission spectrum, and, when used in the slanting
animal tunnel of the ORNL Graphite Reactor, emits
2 x lo8 fission neutrons/cm2*sec near the center
of the plate. A first irradiation of 5.8 x 1013
neutrons/cm2 introduced 1.9 x loi5 acceptors/cm3
in a germanium crystal. This experimental value
agrees to within a factor of 2 with the calculated
value of 3.4 x 10'5.
The result of the first experiment indicates that
the present assumptions on the variation of dis-
placements with neutron energy are roughly correct.
This will be checked by further irradiations with
fission neutrons and with 30-kev neutrons from
the antimony-beryllium photoneutron source. More
adequate neutron monitoring is to be used for
future germanium irradiations. This may lead to a
complete understanding of displacements in at
least one solid-state reaction.
26D. Binder, Solid State Semiann. Prog. Rep. Feb.
29, 19.56. ORNL-2051, p 48.
P ERlOD ENDfNG JUNE 10, 1956
VISCOMETER FOR REMOTE MEASUREMENTS
OF THE VISCOSITY OF 1RRADIATED
FUSED-SALT FUELS
C. C. Webster
A viscometer was designed for use in a hot cell
which will be capable of measuring the viscosities
of irradiated fused-salt fuels at temperatures up
to about 7WC in an inert (helium) atmosphere
within a shielded cell. The apparatus consists of
two vessels, 6 in. long, 1.25 in. OD, mounted in
a vertical position, with 2 in. between centers. An
lnconel tube 3 ft long and bent into a U-shape
connects the bottoms of the vessels. A small
ferromagnetic ball travels with the liquid through
the tube, and the position of the ball is detected
at two points on each leg of the U-tube by elec-
tronic equipment.
Swagelok connections are provided at the top
for inserting liquid-level probes and for allowing
helium pressure to be applied on the surface of
the liquid in either vessel. The whole apparatus
is inserted into a 4-in.-dia vertical furnace with
an 18-in. controlled-temperature heated zone. End
heaters are provided to control the heat loss out
the ends of the furnace.
EFFECTS OF RADIATION ON
ELECTRICAL COMPONENTS
J. C. Pigg C. C. Robinson27
Insulation
In previous e~periments~~e~~ on the effect of
radiation on electrical insulation the insulated
wire to be irradiated was placed in the reactor as
if it were a sample lead. Care was taken to ensure
that possible leakage paths from the central conductor
to the shield were as long as possible.
Whenever practicable, the end of the insulation
that was in the reactor was sealed over at the end
of the central conductor. However, the possibility
of conduction by end surfa contamination and
ionization of the air still existed when there was
no seal or when the seal was defective.
In order to determine whether such leakage was
important in the experiments previously conducted,
270n assignment from Wright Air Development Center.
28.1 C. Pigg and C, C. Robinson, Solid State Semiann.
Prog. Rep. Aug. 30, 1995, ORNL-1945, p 6.
--
"J. C. Pigg et al.. Communication and Electronics
22, 717 (January 1956).
243