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:
AA00009214:00009


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k- 7r-2 7


CLASSIFIED BNL-2027
Subject Category: PHYSICS



UNITED STATES ATOMIC ENERGY COMMISSION



THE TRANSMISSION OF NEUTRONS AND
GAMMA-RAYS THROUGH AIR SLOTS.
PART DI. THERMAL AND EPITHERMAL
NEUTRON DISTRIBUTIONS AROUND
SAN AIR SLOT IN WATER
0
By
Robert D. Schamberger
Ferdinand J. Shore
Harvey P. Sleeper, Jr.






September 1, 1954 ( r 1956

Brookhaven National Laborato /
Upton, New York -*


1*( '.) *1 Technical Information Service, Oak Ridge, Tennessee







UNCLASSIFIED


p"i UNCLASSIFIED
ii"





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 15 cents. Available from the
Office of Technical Services, Department of Commerce, Wash-
ington 25, D. C.


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.





BNL-2027


THE TRANSMISSION OF NEUTRONS AND GAMMA-RAYS THROUGH AIR SLOTS


Part IX

Thermal and Epithermal Neutron Distributions around an Air Slot in Water


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




1 September 1954





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






REACTOR DEPARTaiNT

BROOKHAVEN NATIONAL LABORATORY
Associated Universities, Inc.

under contract with the
United States Atomic Energy Commission





ThE Trf.-Si:ISSIO'] OF NEUTRONS AND CAJ1.A-RAYS THROUGH AIR SLOTS


Part IX


Thermal and Erit!er mal 'eutron Distributions around an Air Slot in water r


INTRODUCTION

This particular experiment is one of a group designed to shed further
light on the processes taking place in neutron transmission through air slots.
The method was to study in detail the flux distributions in water around an air
slot.

SECTION 1
Experimental Arrangement

For this experiment, a special air slot was fabricated of one inch
thick lucite walls. The dimensions of the slot were 1 x 33 x 45 inches, with
the forty-five inch dimension vertical. The bottom of the air slot was 4.5
inches from the bottom of the water-filled BNL shielding tank. The slot was
constructed in this way so that there would be negligible boundary effects and
the detector could be placed relatively close to the air slot boundaries.
Measurements were made with a one-inch diameter, six inches long, BF counter,
with and without a cadmium cover. A few measurements in the region rf high flux
were made with a natural uranium fission chamber.

SECTION 2
Experimental Results

Figure 1 shows the results for typical vertical and horizontal thermal
neutron traverses made above the forty-five inch air slot in water. The upper
end of the air slot was at Z = 49.5 inches, and the horizontal traverse was made
at Z = 54 inches. As determined from the Z traverse, the neutron relaxation
length was: seven inches above the slot -- cm; and, twenty-five inches above
the slot -- 7.7 cm. This indicated a hardening of the transmitted spectrum.

Figure 2 shows a series of vertical traverses made parallel with the
vertical axis of the air slot in water. The most striking feature of these
curves was the peak in the thermal flux opposite the end of the air slot. This
indicated the presence of a localized low energy source at the end of the air
slot, which is significantly more intense than the radiation transmitted through
the sides of the slot. Figure 3 shows the same information with the water back-
ground subtracted from the datal, so that the effect due to the slot alone is
determined. Figure 4 shows similar curves measured with a cadmium-covered BF3
detector, showing the same general characteristics.


Background data have not been subtracted in Figures 1, 2, and 4.







Figure 5 shows the general features of the attenuationr of the trans-
mitted radiation in water as a plot of thermal neutron isodoses around the end
of the air slot. Those isodoses were generated from data which had been cor-
rected for the effect of the water background. In general, the neutron isodoses
were roughly elliptical above the slot and roughly parallel with the slot along
the upper end. They tended to branch out near the bottom of the slot. It was
not possible to obtain reliable measurements over a larger area because of the
high background from the normal water transmission. The "elliptical" isodoses
constituted definite evidence of a strong forward or collimated high energy
component. This is in contrast with the semicircular isodoses previously ob-
served in measurements of the transmission of intermediate energy neutrons through
iron slabs2. Also, close to the end of the slot, there was definite evidence of
roughly circular isodoses, corresponding to a localized low energy source.

The evidence for the former remarks, concerning the collimated com-
ponent, is sown more strikingly in Figure 6, comparing the attenuation of thermal
neutrons vertically and horizontally opposite the end of the slot. It is evident
that the vertical traverse has a considerably longer relaxation length than the
horizontal traverse far out in the water.

In the past, suggestions have been made that one might study the
transmission of neutrons through a duct by making measurements in water along
the side of a duct, rather than behind the end of ducts of varying lengths. To
study this and associated questions, a measurement was made in detail down the
length of the special lucite-walled air slot in water, four inches from the
centerline of the slot. This measurement is shown in Figure 7. The results
indicated that the radiation could be divided into two components: that trans-
mitted to the end of the duct; and, that transmitted through the sides of the
duct,

As demonstrated in Part IT of this series, the portion transmitted
through the end of the slot varies with the inverse square of the slot length
for this particular geometry. The data in Figure 7 indicate that the portion
transmitted through the- sides varies as the inverse fourth power of the slot
length. 1While the contribution of the inverse fourth power component to the
flux measured immediately above the forty-five inch long slot was quite small,
it could become an important fraction for shorter ducts.


2 BIlL-265 "The Streaming of INeutrons in Carbon Steel", Shore, Schambcrgor,
and Sleeper, Jr. (i Dec 53)









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