Memorandum from Arthur Waltner to Clifford K. Beck
1 p.
October 17, 1951

October 17, 1951

TO: Clifford K. Beck
FROM: Arthur Waltner CC: Reactor Committee
SUBJECT: Neutron Detectors
REFERENCE: Conference, J. E. Bins, Brookhaven
National Laboratory

A. The Brookhaven reactor does not use fission chambers for measurement and
control of the reactor. A few experimental fission counting chambers have been
used. These are parallel plate chambers using three circular plates on which. U235
has been deposited electrolytically. These plates are available from the K-25
plant at Oak Ridge.

B. Boron can be most easily deposited on the walls of an ion chamber if it
is in the form of an oil slurry. It is available in such a form through the AEC
at about $16.00 par grain. Dr. Joseph Gundlach of Oak Ridge has complete informa-
on this technique.

C. Aluminum, steel, or graphite all make satisfactory chamber material for
coating by the above process. Some chambers, in fact, use steel and aluminum in
the same chamber. In the judgment of Mr. Bins aluminum is probably better than
steel as a chamber material.

D. A normal boron chamber having a diameter of 3 inches and a length
of 30 inches produces a current of 270 microamperes, when one end is in a flux
of 1011n/cm² sec. The position of this chamber is such that the flux gradient is
great so that the mean flux is considerably less than the stated value.

E. A compensated chamber consisting of two identical chambers, one coated
with boron and the other uncoated has been developed to minimize the gamma back-
. This chamber has a graphite electrode and a magnesium shell. It is
observed that this chamber reduces the gamma background by a factor of 107.
Information on this chamber is available from Dr. Gundlach of Oak Ridge.

F. It has not been necessary to use rigid coax to the detectors of the
Brookhaven Reactor. Ordinary polycthelene coax cable is used.