Exercise 4:
Resonance Doppler Broadening




This exercise will make use of the RECONR and BROADR modules to reconstruct the resonance cross sections for Pu-238, broaden them to 10000K, and plot a comparison of the 0K and 10000K cross sections.

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 in4 containing the following lines (as usual, you can leave off the comments to the right of the slash symbol): 

           reconr
           20 21
           'exercise 4'/    new tape ID title
           1050 1/          MAT
           .01/             fractional tolerance
           '94-Pu-238'/     descriptive card for new tape
           0/
           broadr
           20 21 22
           1050 1/          MAT, one temperature
           .01/             tolerance
           10000/           temperature
           0/
           plotr
           23/              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
           2 4 .5/          x-axis range and step
           /                default label
           .1 1000/         y-axis range
           /                default label
           4 21 1050 3 102 0./ data source for curve
           1 3 0/           crosses with solid line
           2/               second curve on axes
           4 22 1050 3 102 10000./ data source for curve
           0 0 1/           crosses with dashed curve
           99/              finished
           viewr
           23 24/
           stop

Run the NJOY job, and then use ghostview or any Postscript printer to look at the results on tape24. You can see how the Doppler broadening changed the sharp 0K resonance into the broader resonance appropriate to 10000K. We added crosses at the energy grid points to show how the grid is adjusted with temperature. Note the the grid points are very close together near the resonance energy for the 0K curve, and more widly spaced out on the shoulders of the curve. The broadened curve, on the other hand, has widely spaced points near the resonance energy, and the closely spaced points appear out on the steep descents at the "Doppler width."

Variations: change the energy range being plotted to 100 to 200 eV with steps of 20 eV. Change the reaction being plotted to elastic scattering. These graphs will look better if you take off the crosses (e.g., use "0 0 0/" and "0 0 1/" for the curve styles).


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