Memorandum from A. C. Menius, Jr. and R. L. Murray to C. K. Beck

%MurNBwindow041751; %MurNBwindow041751forms; ]> Memorandum from A. C. Menius, Jr. and R. L. Murray to C. K. Beck [a machine-readable transcription] Murray, Raymond L. Menius, A. C., Jr. Creation of machine-readable version: Russell S. Koonts Creation of digital images: Russell S. Koonts Conversion to TEI.2-conformant markup: NCSU Science and Technology Electronic Text Center. ca. 9 kilobytes NCSU Libraries. Raleigh, NC. Modern English, MurNBwindow041751

Available from: NC State University Archives

Publicly-accessible

URL: http://www.lib.ncsu.edu/archives/etext/engineering/reactor/murray/

2000

Nuclear Reactor Digitization Project

Raymond L. Murray Reactor Project Notebook

Illustrations have been included from the print version. Scanned by Russell Koonts with Photoshop 5.0 software. Memorandum from A. C. Menius, Jr. and R. L. Murray to C. K. Beck <author>Raymond L. Murray</author> <author>A. C. Menius, Jr.</author> <respStmt> <resp/> <name/> </respStmt> </titleStmt> <editionStmt> </editionStmt> <extent>3 pp.</extent> <publicationStmt> <publisher></publisher> <pubPlace></pubPlace> <date></date> <idno>Manuscript copy consulted: NCSU Libraries call number UA105.16</idno> </publicationStmt> <seriesStmt> </seriesStmt> <notesStmt> <note></note> </notesStmt> </biblFull> </sourceDesc> </fileDesc> <encodingDesc> <projectDesc> Prepared for the NCSU Libraries Science and Technology Electronic Text Project. </projectDesc> <editorialDecl> Spell-check and verification made against printed text using Notetab spell checker. The lineation of the manuscript has been maintained and all end-of-line hyphens have been preserved. The images exist as archived TIFF images, one or more JPEG versions for general use, and thumbnails. Keywords in the header are a local Electronic Text Center scheme to aid in establishing analytical groupings. </editorialDecl> <refsDecl> ID elements are given for each page element and are composed of the text's unique cryptogram and the given page number, as in NEprop033050a for the title page of Clifford Beck's Proposal. </refsDecl> <classDecl> <taxonomy id="LCSH"> <bibl> <title>Library of Congress Subject Headings April 17, 1951 English non-fiction; prose LCSH 24-bit color; 400 dpi Memorandum from A. C. Menius, Jr. and R. L. Murray to C. K. Beck Typescript 3 pp. April 17, 1951 MurNBwindow041751

April 17, 1951 NCSC-15 TO: C. K Beck FROM: A. C. Menius, Jr. and R. L. Murray SUBJECT: Water Window Thickness A. Thermal Column

The position of the window relative to the thermal column and nearest exposure port is shown below:

To obtain the order of magnitude of radiation at the window scattered from the thermal beam, a calculation of the flux at the point P (see figure above) was made.

The flux at this point due to the scattering from a volume dσdχ is given by

in which we have taken the probability of the neutron reaching P after scattering to be unity. This is realistic in that the mean free path in air for the neutron is several thousand centimeters. Also φ is considered constant along χ. This is a good approximation and is on the safe side.

The above equation can be written as

Assuming that the increase in the φs contribution on the left of the center line in beam will nearly be compensated by decrease on the right, we may intergrate dσ directly, giving

The average number of atoms will be

= 0.89 x 6 x 1019 = 5.4 x 1019 and since the weighted (O and N) thermal scattering cross-section is about 9 x 10-24 cm2, we have Σs = 4.9 x 10-4

Assuming a 4' x 4' beam with a flux of 107 m/cm2sec and Ro = 19' we have at a point 7' from the edge of window a flux of

= 2.5 x 104 m/cm2sec

The above value is based upon calculations assuming a collimated bean. This will not be exactly true. For a bean which is not collimated we can write

= 3.5 x 104 n/cm2sec.

The correct value will be somewhere between the two. Assuming the larger value to be correct and a tolerance of 1000 n/sec cm2 for thermal neutrons, the window thickness should be given by

This leads to a thickness of x = 10cm.

B. Experimental Port

At the experimental ports when open there will be a collimated flux of 2 x l08 n/cm2sec for fast neutrons and 1.2 x 107 n/cm2sec. slow neutrons. Substituting in the first equation with A = 180 cm2 and Σs = 5.4 x 10-3

= 720 n/cm2sec

Since H20 is comparable to Portland cement in attenuation of fast neutrons, a 6" window will reduce the fast neutron component below tolerance.

The slow neutron flux at the window will be given by

≃ 3.25 x 104 n/cm2sec. Adding to this the fast neutron flux which has been assumed thermalized gives a window thickness as before of ~ 10 cm.

To be completely safe it is believed a window of 6 inches should be used with Borax added to enhance slow neutron absorption as well as some fast.