Exercise 3: Resonance Cross Sections





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:

         [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

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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15 December 2012 T-2 Nuclear Information Service ryxm@lanl.gov