H in CH2
H(CH2) GA EVAL-DEC69 KOPPEL,HOUSTON,SPREVAK
REF.1 (1978) DIST-MAY10 20100309
----JENDL-4.0 MATERIAL 37
-----THERMAL NEUTRON SCATTERING DATA
------ENDF-6 FORMAT
==================================================================
The data were taken from ENDF/B-VI.8.
==================================================================
TEMPERATURES = 296 350 DEG K.
HISTORY
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THIS EVALUATION WAS PRODUCED AT GENERAL ATOMIC IN 1969 USING
THE GA CODES GASKET AND ZREND (SEE REF.1). IT WAS CONVERTED
TO ENDF-6 FORMAT AT LOS ALAMOS IN 1989. THE ONLY CHANGES
MADE TO THE CONTENTS WERE ADJUSTMENTS OF CROSS SECTIONS
TO MATCH THE ENDF/B-VI VALUES.
THEORY
------
POLYETHYLENE IS REPRESENTED USING A MODEL OF NONINTERACTING
CHAINS OF CH2 RADICALS ORIGINALLY DEVELOPED BY LIN AND KOENIG
(REF.2). THE DISPERSION RELATION OF POLYETHYLENE SHOWS NINE
BRANCHES, THE FREQUENCY IN EACH BRANCH BEING A FUNCTION
OF THE PHASE DIFFERENCE OF THE VIBRATIONS OF CORRESPONDING
ATOMS IN NEIGHBORING CH2 UNITS. FOR SOME NORMAL MODES, THE
RATIO OF THE AMPLITUDE OF THE HYDROGEN ATOM VIBRATIONS TO THE
AMPLITUDE OF THE CARBON ATOM VIBRATIONS ALSO DEPENDS STRONGLY
ON THE PHASE DIFFERENCE. USING THIS MODEL, THE FREQUENCY
SPECTRUM WAS COMPUTED EXACTLY FOR THE HYDROGEN ATOMS IN HISTOGRAM
FORM (REF.3). THE LOW FREQUENCY PART OF THE HISTOGRAM (BELOW
0.02 EV) WAS THEN REPLACED BY A DEBYE SPECTRUM HAVING THE SAME
AREA, AND THE OTHER ELEMENTS OF THE HISTOGRAM DISTRIBUTION WERE
REPLACED BY GAUSSSIAN FUNCTIONS OF APPROPRIATE AREA CENTERED AT
THE CENTER OF EACH INTERVAL OF THE HISTOGRAM. THE GA CODE
GASKET WAS THEN USED TO OBTAIN S(ALPHA,BETA). THE ELASTIC
PART OF THE SCATTERING LAW IS REPRESENTED USING THE
INCOHERENT APPROXIMATION WITH DEBYE-WALLER INTEGRALS FROM THE
GASKET CALCULATION (SEE REF.1). THIS EVALUATION ONLY GIVES
THE SCATTERING FROM THE HYDROGEN IN POLYETHYLENE. THE CARBON
SHOULD BE TREATED AS A FREE GAS WITH MASS 12.011 AMU.
REFERENCES
----------
1. J.U.KOPPEL AND D.H.HOUSTON, REFERENCE MANUAL FOR ENDF THERMAL
NEUTRON SCATTERING DATA, GENERAL ATOMIC REPORT GA-8774
REVISED AND REISSUED AS ENDF-269 BY THE NATIONAL NUCLEAR
DATA CENTER, JULY 1978.
2. T.P.LIN AND J.L.KOENIG, J.MOLEC.SPECTRA 9, 228 (1962).
3. D.SPREVAK AND J.U.KOPPEL, NUCLEONIK 12, 87 (1969).