Add physical units in user's guide, TallyDerivative link

docs/source/pythonapi/index.rst

@@ -135,6 +135,7 @@ Constructing Tallies
    openmc.EnergyFunctionFilter
    openmc.Mesh
    openmc.Trigger
+   openmc.TallyDerivative
    openmc.Tally
    openmc.Tallies
 

docs/source/usersguide/input.rst

@@ -87,6 +87,22 @@ be validated using the following command:
 
    /opt/openmc/bin/openmc-validate-xml
 
+--------------
+Physical Units
+--------------
+
+Unless specified otherwise, all length quantities are assumed to be in units of
+centimeters, all energy quantities are assumed to be in electronvolts, and all
+time quantities are assumed to be in seconds.
+
+======= ============ ======
+Measure Default unit Symbol
+======= ============ ======
+length  centimeter   cm
+energy  electronvolt eV
+time    second       s
+======= ============ ======
+
 --------------------------------------
 Settings Specification -- settings.xml
 --------------------------------------

openmc/tally_derivative.py

@@ -23,12 +23,12 @@ class TallyDerivative(EqualityMixin):
 
     Parameters
     ----------
-    derivative_id : Integral, optional
+    derivative_id : int, optional
         Unique identifier for the tally derivative. If none is specified, an
         identifier will automatically be assigned
     variable : str, optional
         Accepted values are 'density', 'nuclide_density', and 'temperature'
-    material : Integral, optional
+    material : int, optional
         The perturubed material ID
     nuclide : str, optional
         The perturbed nuclide. Only needed for 'nuclide_density' derivatives.
@@ -36,11 +36,11 @@ class TallyDerivative(EqualityMixin):
 
     Attributes
     ----------
-    id : Integral
+    id : int
         Unique identifier for the tally derivative
     variable : str
         Accepted values are 'density', 'nuclide_density', and 'temperature'
-    material : Integral
+    material : int
         The perturubed material ID
     nuclide : str
         The perturbed nuclide. Only needed for 'nuclide_density' derivatives.