diff --git a/docs/source/pythonapi/data.rst b/docs/source/pythonapi/data.rst
index 95fdfeca9..6f5c006c2 100644
--- a/docs/source/pythonapi/data.rst
+++ b/docs/source/pythonapi/data.rst
@@ -63,6 +63,7 @@ Core Functions
     atomic_weight
     dose_coefficients
     gnd_name
+    half_life
     isotopes
     linearize
     thin
diff --git a/openmc/material.py b/openmc/material.py
index e49696706..70cfa7ade 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -152,9 +152,10 @@ class Material(IDManagerMixin):
         for key, value in atoms_per_barn_cm2.items():
             half_life = openmc.data.half_life(key)
             if half_life:
-                atoms = value[1] * self.volume * 1e24
-                activity = math.log(2) * atoms / half_life
+                atoms = value[1] * self.volume
+                activity = atoms / half_life
                 total_activity += activity
+        total_activity = math.log(2) * total_activity * 1e24
 
         return total_activity
 
diff --git a/setup.py b/setup.py
index b2e3f160a..477f29dec 100755
--- a/setup.py
+++ b/setup.py
@@ -32,7 +32,7 @@ kwargs = {
     # Data files and libraries
     'package_data': {
         'openmc.lib': ['libopenmc.{}'.format(suffix)],
-        'openmc.data': ['mass16.txt', 'BREMX.DAT', '*.h5'],
+        'openmc.data': ['mass16.txt', 'BREMX.DAT', 'half_life.json', '*.h5'],
         'openmc.data.effective_dose': ['*.txt']
     },