Adding note on use of nuclide list and consequences for electron/positron interactions

Author: pshriwise

docs/source/io_formats/settings.rst

@@ -98,6 +98,11 @@ sub-elements:
     A list of strings representing the nuclide, to define specific
     define specific target nuclide collisions to be banked.
 
+    .. note::
+        Electron and positron collision-track events are not associated with a
+        specific nuclide. If a ``nuclides`` filter is specified, these events
+        do not match the filter and are omitted.
+
     *Default*: None
 
   :reactions:

docs/source/usersguide/settings.rst

@@ -792,6 +792,12 @@ collision_track.h5 file at the end of the simulation. The file contains
 300 recorded collisions that occurred in materials with IDs 1 or 2, involving
 fission or (n,2n) reactions on the nuclides U-238 or O-16, within cells
 with IDs 5 and 12.
+
+.. note::
+   Electron and positron collision-track events are not associated with a
+   specific nuclide. If a ``nuclides`` filter is specified, these events do not
+   match the filter and are omitted.
+
 The file can be read using :func:`openmc.read_collision_track_file`.
 The example below shows how to extract the data from the collision_track
 feature and displays the fields stored in the file: