A-f?:!! ^^J ^^-^'ASSIFIED UNCLASSIFIED BNL-2025 Subject Category: PHYSICS UNITED STATES ATOMIC ENERGY COMMISSION THE TRANSMISSION OF NEUTRONS AND GAMMA-RAYS THROUGH AIR SLOTS. PART VII. THE EFFECT ON THE NEUTRON TRANSMISSION OF CHANGING THE WALL MATERIAL 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 was prepared as a 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 maynot infringe privately owned 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. 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 I5 cents. Available from the Office of Technical Services, Department of Commerce, Wash- ington 25, D. C. BNL-2025 THE TRANSMISSION OF NEUTRONS AND GAMMA-RAYS THROUGH AIR SLOTS Part VII The Effect on the Neutron Transmission of Changing the Wall ^kte^ial 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-l6 REACTOR DEPARTMENT BROOKHAVEN NATIONAL LABORATORY Associated Universities j Inc. under contract with the United States Atomic Energy Commission Part VII The Effect of Changing the Wall Material of an Air Slot on the Neutron Transmission of the Slot The task of relating experimental information of the type pre- sented in this series of reports to the particular reactor shield with which the designer is concerned is often more nearly an art than a science. In the investigation of the neutron transmission through air slots, we have made a serious attempt to investigate the effect of varying enough of the parameters to make the job of the shield designer as simple as possible. One of those parameters which has been investigated is the material con- stituting the wall of the slot. This report contains the data which we have obtained relating to the variation of this parameter. To obtain a reasonable amount of information with a small number of measizrements, we have used a single slot thickness to investigate the effect of changing the wall material, Vihen the air slot thickness is large, it is reasonable to expect the effect of the walls to be less important than when the slot thickness is small. However, if the slot thickness is made too small, the construction of the slot will not be sufficiently reproducible to measure accurately the change in the transmission resulting from an alteration in the wall material. The slot thickness which was chosen as being reasonably small and yet readily reproducible was 0,^0 inch, . Since steel is the material which usually forms the walls of a practical air slot, the water equivalent walls of a 0,50 x 3^ x -48 inch straight air slot were replaced with O.'^O inch steel sheet. Thermal neutron data above the slot with both lucite and steel walls are presented in Figs. 1 and 2. It is evident from the vertical traverses shown in Fig. 2 that the 30 per cent reduction in thermal flux on introducing the steel walls noted immediately above the slot does not persist as the detector is raised. The fast neutron flux is not, therefore, materially affected by the change. The difference between the two curves in the vicinity of Z = 80 Inches is be- lieved to be the result of a difference in the photoneutron backgroiond. Since the effect of changing the wall material Is expected to be more important for an offset slot where the direct transmission has been greatly reduced, a comparison has been made between a O.'^O x % x /^.8 inch slot with a 1.80 Inch offset located in the middle with lucite and with 0.50 inch steel walls. The thermal neutron traverses above the slot are presented in Figs. 3 and U» The vertical traverses in Fig, U indicate a reduction of about a factor of three close to the slot with the effect of the steel walls becoming much less when the detector was moved several Inches away from the slot. The photoneutron backgrounds are not known with sufficiunt accuracy for these special situations to permit an accurate sub- traction of the effect. The next step in the investigation was to introduce a 1.8 X 34. X 3 inch steel bar at the offset of the lucltc-walled slot, mentioned above, since it was felt that the material near the offset would probably be more effective than material located at other positions in the slot. The - location of the steel bar is indicated in the sketch in Fig. 5. That figure also shows vertical traverses obtained with a thermal neutron detector above the slot for three conditions of the slot: (l) no steel in the walls; (2) the 1.8 X 34- X 3 inch steel bar located at the offset; and, (3) the steel bar at the offset and a cadmium sheet in the middle of the upper section. It may be noted that the steel bar has about the same effect on the trans- mission as the one-half inch steel walls over the entire slot. With the steel bar in place, the reduction in the fast flux was about 2$ per cent. The introduction of the cadmium fiirther reduced the low energy component without affecting the fast neutrons. On the basis of these measurements, we have concluded that the fast neutron transmission of an air slot is essentially independent of the wall material. The low energy component, however, can be affected, pre- sumably by the introduction of material with a large absorption cross section. 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