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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
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MISTER
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OCT 3015-7
"Letter to Liitor of Nucloar science and Engineerin:
;
LITICE VIBRATION FREQUENCY SPECTRUM OF GRAPHITE*
Tranum. Tamo
HOL FOR DUBLIC RELEASE - OFFICIAL
a
The frequency spectrum of the lattice vibrations of graphite linds
uprlication in neutron theralization stuliol, Yoshlinori ani Kitanol
have given a theory of these vibrations and computed the spectrum by
Houston's rathoil, which lows not require large soule cougjuters but doos
introduce spurious peaks Into the spectrum. Here the spectrum has been
calouluted by computer by the root-samling method, namely ly solving the
equation for the frequencies at a large number of uniformly .thetributed
points in the Brillouin zone, and plotting a histograin of the nuuber of
frequoncios falling within slirferent froquancy intervala, Pue figure
shows the rosults both for movies of vibration in the plane ot the hexagon
of the graphite lattice and for modes normal to that piano. For the two
types of modes respectively, 180,000 aud 10,000 froquancies were alcu-
lated for 1/12 of the Brillouin zone, which 19 equivalent to the other
11/12 by wyswetry. There are noticeable differences between the results
here and those shown in references 1 and 3,
It has been shown that in a graphite reactor the thorral neutron
spectrum 18 not very sensitive to the detailed shape of the graphite
vibration frequency spectrum, but one wonders whether the 111ferences noted
above are sufficient to affect the neutron spectrum significantly. To test
id
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1A. Yoshimori and Y. Kitano, J. Paye. Soc. Jupun, 11, 352 (1956).
2W. V. Houston, Rev. Mod. pays., 20, 161 (1948).
Sy. P. Wikner, G. D. Joanou, and D. E. Parks, Nucl. Sci. Eng., 19, 108
(1964).
"Research sponsored by the U. 8. Atomic Energy Commission under contract
with the Union Carbide Corporation......
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this, cole SUMOT Wuo usoj to generate yoatteriny kornois corresponding
to the ruphite vibrution spectru calculated by Houston's mothod and the
root-samplins lethol, and the two scuttering kernols vorn in turn used
to calculate neutron spectra In a lufinite medium of graphito, at a
temperature of 300°K, un poisoned to an absorption of 0.4 barns/carbon
atom with u 1/v absorber; the wirference between the neutron fluxos (B)
for the two different kernels wus lebo thun 2% for all energies.
John V. Wilson
Oak Riütye National Luboratory
Oak Ridge, Tennessee
"J. Bell, SUMMIT, AU TBM-7090 Prograin for the Congputation of
Crystalline Scattering Kemela, USABC Roport CA-2492, General Aconia
(February 1962),

0.2619 •*
- Total Modos
Modos in Plano of Hoxogon
Brities in this modos Normal to plans of Hoxagon
plw)
mooie
an
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10
20
30
40
50
60
70
80
90
100
94 w
LATTICE VIBRATION FREQUENCY SPECTRUM OF GRAPHITE
END


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DATE FILMED
10/14/65