The transmission of neutrons and gamma-rays through air slots

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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:
AA00009214:00007


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UNCLASSIFIED


BNL-2024

Subject Category: PHYSICS



UNITED STATES ATOMIC ENERGY COMMISSION



THE TRANSMISSION OF NEUTRONS AND
GAMMA-RAYS THROUGH AIR SLOTS.
PART VI. THE EFFECT OF MULTIPLE
OFFSETS ON THE NEUTRON TRANSMISSION
OF AN AIR SLOT


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


September 1, 1954

Brookhaven National
Upton, New York


"IM 1 1956



Laboratry.....


Technical Information Service, Oak Ridge, Tennessee


,. P-7..-,













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-2024


THE TRANSMISSION OF NEUTRONS AND GAMI-RAYS THROUGH AIR SLOTS


Part VI

The Effect of Multiple Offsets 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 DEFART"ENT

EROOKHAVEN NATIONAL LaLORATORY
Associated Universities, Inc.

under contract with the
United States Atomic F~ergy Conmission







Part VI

The Effect of Multiple Offsets rn the Neutron Transmission of an Air Slot



This investigation has considered two types of slots containing
more than one offset. In the first type, all of the offsets are smaller than
the slot thickness and they are arranged so that a straight-through slot still
exists. The other case involves slots for which the offsets are large con-
pared with the slot thickness. The situation in which one or more of the
offsets is only slightly larger than the slot thickness has not been studied
because of the difficulty in fabricating such slots reproducibly.

When a straight-through slot exists, as in the first type men-
tioned aboye, we might expect that the offset slot would behave as a straight
slot whose thickness was determined by the effective defining edges of the
offsets. Runs 1915 and 1916, see Figs. 2 to 4, consist of traverses above
a 0.5 inch slot containing two 0.25 inch offsets. The traverses are very
similar to those which have been obtained with a 0.25 inch straight slot in
qualitative agreement with our expection.

With offsets which are large compared with the slot thickness, the
reproducibility of the measurements is good. Data which have been obtained
with large offsets may be used to test the simple assumption that one may
estimate the transmission of a slot with multiple offsets in a straightfor-
ward manner on the basis of the transmission of similar slots with only one
offset. The following paragraph is an attempt to estimate, on such a basis,
the peak transmittal flux of a slot containing two offsets.

Consider the case, illustrated in Fig. 1 opposite, of a slot of
overall length, L, containing two offsets with the first offset a distance
rl from the bottom of the slot and the second offset at r2. The thickness
of all the sections is the same and rl is less than r2. The flux observed
at the exit of the slot may be divided, somewhat arbitrarily, into seven
components. Component 1 represents the transmission of the medium and will
be subtracted from all measurements to yield the transmission of the slot.
Components 2, 5, and 7 are each aware of the existence of only one section of
the slot. Components 3, 4, and 6, however, negotiate at least one of the off-
sets. The transmission of the slot, Tr is then:


Tr = Components (4+6) + components (3+5) + component 2

+ component 7







Consider now the two situations A and B, illustrated below, for
which the overall length of the slots is also L. The three components of the
transmitted flux, in addition to the background, are indicated.


A, A3 K






The transmission of the slot with a single offset of r is:

T = Component A2 + component A3 + component A


Similarly when the offset is at r :
2


Tr2


= Component B2 + component B3 + component B
< 3 4


The assumption, mentioned above, which we wish to make is that the
effect of the offset is independent of the changes in spectrum or angular
distribution which the presence of another offset introduces so that the
following equation is valid.


Components (A3 + A )


* components (B2 + B3
T


= components (4 + 6) + components (3 + 5)


where T is the transmission of a straight slot of length L. If we denote
the ratio B2 + B/T by the symbol a2, and the ratio A3 + A4/T by a, equ. 1
may be rewritten as:


Tale2 = components (4 + 6) + components (3 + 5)


Since components A2 and B4 are usually small, al and a2 may be approximated
as follows:


Tr comp A
aI = T T
1T


The transmission of
of experimental (or
straight slots plus

Trr2 T T


T

T


T T
a = r2 comp B4 2
2 -
T T


the slot with two offsets may then be expressed in terms
analytical) transmissions of the single offset and
the small components 2 and 7.
/ T '+
I + component 2 + component 7 (3)







Runs 1869 and 1870, shown in Figs. 2 to 4, indicate the trans-
mission of a 0.5 inch thick slot with two 1.8 inch offsets for which
L = 48 inches, r1 = 12 inches, and r = 36 inches. From the information
presented in Part V of this series o reportsI, a1 = .0172 and a2 = .0083
for measurements close to the end of the slot. Component 7 is small,
about 1 nv/Mw, immediately above the slot and is everywhere smaller than
the background resulting from the transmission through the water medium.
In this example, component 2 may be neglected.

For a point close to the top of the slot:

T'al.a2 + component 7: 6 nv/Mw

The experimental determination of the transmission was

12.5 2.4 = l.01101 nv/Mw.

The measurements 7.5 inches beyond the end of the duct indicated
a total flux about twice the background. The product Tala2 is, however,
appreciably less than the background. For the slot discussed above the
simple assumption which was made leads to an estimate for the transmission
which is of the right order, but which cannot be said to be in good agree-
ment with the observed transmission.

From runs 1898 and 1897, Figs. 5 to 7, it may be seen that the
introduction of a third offset is not very effective. There is an indication
that even if the background (component 1) were much less, the effectiveness
of the third offset would be significantly less than the first or second.
From the practical standpoint, more than two offsets would appear to be
unnecessary.


1 BNL Log No. C-8248






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