The transmission of neutrons and gamma-rays through air slots

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Material Information

Title:
The transmission of neutrons and gamma-rays through air slots
Series Title:
BNL ;
Physical Description:
v. : ill. ; 27 cm.
Language:
English
Creator:
Schamberger, Robert D
Shore, Ferdinand J
Sleeper, Harvey P
Brookhaven National Laboratory
U.S. Atomic Energy Commission
Publisher:
United States Atomic Energy Commission, Technical Information Service
Place of Publication:
Oak Ridge Tenn
Publication Date:

Subjects

Subjects / Keywords:
Nuclear physics   ( lcsh )
Neutrons -- Diffraction   ( lcsh )
Gamma rays   ( lcsh )
Genre:
federal government publication   ( marcgt )
non-fiction   ( marcgt )

Notes

Statement of Responsibility:
by Robert D. Schamberger, Ferdinand J. Shore, Harvey P. Sleeper, Jr.
General Note:
Cover title.
General Note:
Originally published 1954.
General Note:
"September 1, 1954."
General Note:
"Subject category: Physics."
General Note:
"Brookhaven National Laboratory, Upton, New York."
General Note:
"Date Declassified: November 21, 1955."--P. 2 of cover.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 004703692
oclc - 432319550
System ID:
AA00009214:00008


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L- CLASSIFIED


UNCLASSIFIED


BNL-2026

Subject Category: PHYSICS


UNITED STATES


ATOMIC ENERGY COMMISSION


THE TRANSMISSION OF NEUTRONS AND
GAMMA-RAYS THROUGH AIR SLOTS.
PART VIII. THE EFFECT OF THE
SOURCE SIZE ON THE NEUTRON
TRANSMISSION OF AN AIR SLOT

By
Robert D. Schamberger
Ferdinand J. Shore
Harvey P. Sleeper, Jr.


September 1, 1954

Brookhaven National Laboratory
Upton, New York


Technical Information Service, Oak Ridge, Tennessee










Date Declassified: November 21, 1955.


This report has been reproduced directly from the best
available copy.

Issuance of this document does not constitute authority
for declassification of classified material of the same or
similar content and title by the same authors.

Printed in USA, Price 20 cents. Available from the
Office of Technical Services, Department of Commerce, Wash-
ington 25, D. C.


GPC B23200 1


This report was prepared asa scientific account of Govern-
ment-sponsored work. Neither the United States, nor the Com-
mission, nor any person acting on behalf of the Commission
makes any warranty or representation, express or implied, with
respect to the accuracy, completeness, or usefulness of the in-
formation contained in this report, or that the use of any infor-
mation, apparatus, method, or process disclosed in this report
may not infringe privatelyowned rights. The Commission assumes
no liability with respect to the use of,or from damages resulting
from the use of, any information, apparatus, method, or process
disclosed in this report.





THE TRANSMISSION OF NEUTRONS AND GAMMIA-RAYS THROUGH AIR SLOTS


Part VIII

The Effect of the Source Size on the Neutron Transmission of an Air Slot




Robert D. Schamberger
Ferdinand J. Shore
Harvey P. Sleeper, Jr.




1 September 1954







Work performed under Contract No. AT-30-2-Gen-16



















REACTOR DEPARTMENT

BROOKHAVEN NATIONAL LABORATORY
Associated Universities, Inc.

under contract with the
United States Atomic Energy Commission






One of the questions which will be of interest to those who
wish to use the information presented in this series of reports, and
which may be of interest to others as well, is the effect of the spatial
extent of the source on the neutron transmission of an air slot in water.
The method which has been chosen to investigate this question takes.
advantage of the fact that the source plate is continuously movable
The region beneath the slot is scanned with the leading edge of the
forty inch square source plate to determine the relative importance of
the various parts of the source in supplying the transmitted neutrons.
The change in the transmitted flux when the source is moved from position
A to position B is a measure of the flux originating in the regions which
are not common to both position A and position B.

This report presents the data which have been obtained on the
source size effect and a discussion of some measurements which we expect
to make in the near future to aid in answering the questions which these
data have raised.

The procedure which has been used is described below. The
slot was placed in thq tank with its short dimension (T) parallel to the
direction of motion of the source plate. A typical arrangement is shown
in Figure 1. The forty inch square source plate was then moved in small
steps under the tank. For each position of the source plate, either the
fast neutron dose or the thermal neutron flux, or sometimes both, was
measured in the water at a point above the center of the slot. The
resulting curves were differentiated graphically to give the contribution
to the transmitted flux or dose by various line elements of the source.
One set of data was also obtained with the slot rotated through ninety
degrees so that the larger of the horizontal dimensions (W) was parallel
to the direction of motion of the source.

Most of the information has been obtained with a special
3 x 24 x 48 inch slot, shown in Figure 1, which had 0.125 inch steel
walls and rested directly on the tank bottom. In addition, one measure-
ment is available with a 1 x 34 x 48 inch slot in the usual slot holder2.

Figures 2 and 3 contain the data obtained with a F3 counter
and a Hurst-type nondirectional fast neutron dosimeter above the 3 x 24 x 48
inch air slot. Both detectors were located at Z=62 inches, 13.5 inches
above the top of the slot, and both sets of data were obtained at the

1A complete description of the mechanical features of the BNL shieldirg
facility appears in BNL-139
2 A description of the apparatus is given in Part I of this series, B
A description of the apparatus is given in Part I of this series, BNL-2019






same time. The slopes of these curves, corresponding to the contribution
to the measured dose or flux from line elements of the source, have been
plotted in Figures 4 and 5. The contribution of the thermal neutron flux
and the fast neutron dose from the various regions of the source are
quite similar and seem to justify the use to the thermal neutron detector
to measure something proportional to the fast neutron dose when a large
water separation exists between the top of the slot and the thermal
neutron detector. A third set of data using this same slot, which was
obtained with a BF3 counter at Z=64 inches, is shown in Figure 6. The
curve obtained by differentiating these data is shown in Figure 7 in
which the curves presented in Figures 4 and 5 have been included for
comparisdh. The differences between these curves are probably indicative
of the uncertainties in the original data and in the differentiation
process used to obtain these curves from the original data.

The region of the source plate subtended by the angle defined
by the bottom of the slot and the detector is indicated on each of the
figures and is referred to as the region "directly seen" by the detector.
For the three inch slot resting on the tank bottom, at least two thirds
of the exit flux originated in tho region so defined.

The information which was obtained with the 3 x 24 x 48 inch
slot rotated through ninety degrees is given in Figures 8 and 9. These
data illustrate clearly an asymmetry which is not very apparent in the
other curves. When the source plate is centered under the tank, in the
so-called "0" position, a small displacement of the source removes a
section of the source from one side but adds it to the other side, so
that the net change in transmitted neutrons is very small. Soon, how-
ever, the source begins to enter a boral lined magazine located just
north of the tank, so tAat further changes in the source position alter
the location of only one edge of the effective source. The north edge
is determined by the location of the edge of the boral shield in the
magazine. These data, while not conclusive, indicate that the contribution
to the transmitted flux from those portions of the source not "directly
seen" by the detector is quite small.

Unfortunately, the only information which is available for
slots which do not rest on the bottom of the tank was obtained with a
1 x 34 x 48 inch slot which is a little too thin to permit a detailed
analysis of the data or a direct comparison with the three inch slot
resting on the bottom. For this case in which the bottom of the one
inch slot was 3.75 inches above the tank bottom, the data are presented
in Figures 10 and 11. It is apparent that the contribution to the trans-
mitted flux from the region of the source not "directly seen" by the
detector is a larger fraction of the total than was observed with the
three inch slot located at the bottom of the tank. We do not have
sufficient information at the present time to determine the effect of
the distance between the source plate and the bottom of the slot, the
effect of the amount of material between the bottom of the slot and
the source, or the effect of the slot thickness on the region of the
source from which the exit flux originates. It is thought that the
additional material between the bottom of the slot and the source plate







is primarily responsible for the increased contribution from regions far re-
moved from the slot rather than the change in slot thickness being primarily
responsible. The validity of this belief will be investigated by making
measurements with the 3 x 24 x 48 inch slot raised so that there is 3.5
inches of water beneath it. This particular investigation has been post-
poned because the source plate has become somewhat difficult to move.
Measures are being taken to ease the source plate movement.

For all of the measurements the contribution to the trans-
mitted flux from regions of the source which are far removed from the
bottom of the duct is not negligible. It should be noted, however, that
the source plate is 10.6 inches beneath the bottom of the tank so that
neutrons can reach the region of the bottom of the duct from the edges of
the source. One would expect then, that the introduction of appreciable
scattering material beneath the slot would significantly increase the
contribution to the exit flux from the region of the source far from the
slot. To ascertain the effect of the separation between the source
plate and the tank bottom, a special natural uranium source plate,
2" x 40" x 5/8", is being fabricated. This source will be placed in the
tank and moved relative to the slot to determine how the contribution
from the line source depends on the separation between the source and
the slot.







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UNIVERSITY OF FLORIDA
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