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Exercise 3: Resonance Cross Sections
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This exercise will explore how File 2 and File 3 are used
to represent resonance cross sections on a typical ENDF
file. Open the file for Tape 404 from the NJOY97 distribution
in your text editor.
First, search down for the start of MAT1050, MF2, MT151,
the resonance parameters for Pu-238. The structure
of MF2/MT151 for this material is as follows:
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[MAT,2,151/ZA,AWR,0,0,NIS,0] HEAD
[MAT,2,151/ZAI,ABN,0,LFW,NER,0] CONT
[MAT,2,151/EL,EH,LRU,LRF,NRO,NAPS] CONT
data for this part
[MAT,2,151/EL,EH,LRU,LRF,NRO,NAPS] CONT
data for second part
[MAT,2,0/0.,0.,0,0,0,0] SEND
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using the standard ENDF shorthand. The details of this
format are given in the Formal
Specifications for File 2. For now, just look in the file
to find the energy range EL,EH for the first part of the
parameters (the resolved range). Note that LRU=1 (resolved)
and LRF=1 (Single-Level Breit Wigner). How many resonances
are given? The first column shows the resonance energies.
Scan down a little further to find the second part of the
resonance data (the unresolved in this case). What is the
energy rangle EL,EH for the unresolved data? Note that
LRU=2 (unresolved) and LRF=1.
Now search for MF=3, MT=1 (the total cross section). Read
through the file to find the energies corresponding to the
resonances ranges determined above. What total cross section
values are given in the resonance ranges? How are the
boundaries between the nonresonance and resonance ranges
handled? Look at MT2 (elastic), MT18 (fission), and
MT102 (capture). Are the treatments of the resonance range
consistant with that for the total?
In practice, a processing code like NJOY is used to generate
the resonance contribution to the cross sections and combine
them with the numbers in File 3.
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