Exercise 3:
Resonance Reconstruction

This exercise will make use of the RECONR module of NJOY to reconstruct the resonance cross sections for Pu-238 and to examine the results for the first few resonances. Plotting of the cross sections will also be demonstrated.

Copy t404 from the NJOY distribution to tape20. This file contains the ENDF/B-IV version of the Pu-238 cross sections. Create a file named in3 containing the following lines (as usual, you can leave off the comments to the right of the slash symbol):

           20 21
           'exercise 3'/    new tape ID title
           1050 1/          MAT
           .001/            fractional tolerance
           '94-Pu-238'/     descriptive card for new tape

This file says to run RECONR on MAT1050 with a reconstruction tolerance of .001 (.1%). The output will be on tape21. The title on the Tape ID card will be "exercise 3," and the single information line in the output file will say "94-Pu-238." The output is written on tape21.

Run the NJOY job with this input file.

Examine the file called "output" to see the new messages from BROADR. Note that 475 points were added for linearization even before resonance reconstruction began. The resolved resonance range is seen to run from 1 to 200 eV, and an additional 6215 points were added to represent the detailed shapes of the resonances. This particular evaluation uses the single-level Breit-Wigner resonance representation, which can produce negative elastic scattering cross sections, and the message from subroutine EMERGE indicates that that happened here.

Examine the file called "tape21" to see what the new resonance PENDF tape looks like.

  • Check MF=3, MT=2 (elastic scattering). Find the lower limit of the resolved resonance range. What happens to the cross section there?

  • Find the center of the lowest resonance at 2.855 eV. Note that the peak is at higher energies and that there is an interference dip at lower energies.

  • Check the 18.56 eV resonance. Note the place where the interference minimum went negative and was replaced by a small number. This was one of the sources of the message from EMERGE. Note that the energy grid went to a precision of nine significant digits temporarily.

  • Check MF=3, MT=102 (radiative capture). Where is the peak of the lowest resonance in this case?

  • Check MF=3, MT=18 (fission cross section). Where is the peak of the lowest resonance in this case?

  • Check MF=3, MT=1 (total cross section). Note that it is dominated by the capture component.

  • Go back to the beginning of tape21 and look at File 1. Note the directory of sections--only Files 1, 2, and 3 are present. You can also see the Tape ID and comment lines from the input deck, and the third card shows a temperature of 0K and a reconstruction tolerance of 1e-3.

  • Finally, scan down to MF2, MT152. This is a special NJOY section giving the infinitely dilute unresolved resonance range cross section. Note that the unresolved range runs from 200 eV to 10 keV.

Now, modify in3 to contain the following lines to enable the cross sections from tape21 to be plotted:

           22/              output file
           /                default page style
           1/               new axes, new curve
           '94-Pu-238'/     title line 1
           /                no line 2 for titles
           2/               lin x - log y
           1 5 1/           x-axis range and step
           /                default label
           .1 1000/         y-axis range
           /                default label
           4 21 1050 3 102/ data source for curve
           /                default curve style
           2/               second curve on axes
           4 21 1050 3 2/   data source for curve
           0 0 1/           dashed curve
           3/               third curve on axes
           4 21 1050 3 18/  data source for curve
           0 0 4/           dotted curve
           99/              finished
           22 23/

Run the NJOY job, and then use ghostview or any Postscript printer to look at the results on tape23. The solid curve is the capture cross section, the dashed curve is the weak elastic resonance, and the dotted line shows the weak fission resonance.


23 January 2013 T-2 Nuclear Information Service ryxm@lanl.gov