This keyword specifies the binning of the discrete photon spectral lines into histograms for use in the decay γ source spectrum. In order to use this feature, three things are required:

1. Add the keyword within the library preparation section of the input file(s)
2. Include a file with the requested gamma group structure
3. Add the gamma group file in the files file as ggbins

To add the keyword within the library preparation section of the input file, place the keyword before the GETDECAY keyword:

< -- Control phase -- >
...
GETDECAY 1
FISPACT
* Title of the simulation
< -- Initial phase -- >
...
< -- Inventory phase -- >
...


The format of the gamma group file is:

[N number of groups]
Energy 0
Energy 1
...
Energy N


with N+1 energies in ascending order and with units of eV. Note that zero is not allowable as a first energy. An example would be:

5
1.0
1.0E+05
5.0E+05
1.0E+06
2.0E+06
1.0E+07


The location of this file must be added with the ggbins path in the files file:

# gamma spectrum group energy bins
ggbins /path/to/gamma_group_file


Alternatively, READGG can be placed in a stand-alone condense input, for example the various arrayx.i of the fispQA/Tst_ggs/. Note that if this is done, all calculations which employ the condensed ARRAYX data will use that gamma group structure specified in the condense.