New multiply_density option on tallies (#2539)

docs/source/io_formats/statepoint.rst

@@ -139,6 +139,8 @@ The current version of the statepoint file format is 17.0.
              - **internal** (*int*) -- Flag indicating the presence of tally
                data (0) or absence of tally data (1). All user defined
                tallies will have a value of 0 unless otherwise instructed.
+             - **multiply_density** (*int*) -- Flag indicating whether reaction
+               rates should be multiplied by atom density (1) or not (0).
 
 :Datasets: - **n_realizations** (*int*) -- Number of realizations.
            - **n_filters** (*int*) -- Number of filters used.

docs/source/io_formats/tallies.rst

@@ -69,6 +69,12 @@ The ``<tally>`` element accepts the following sub-elements:
     list of valid scores can be found in the :ref:`user's guide
     <usersguide_scores>`.
 
+  :multiply_density:
+    A boolean that indicates whether reaction rate scores should be computed by
+    multiplying by the atom density of a nuclide present in a material.
+
+    *Default*: true
+
   :trigger:
     Precision trigger applied to all filter bins and nuclides for this tally.
     It must specify the trigger's type, threshold and scores to which it will