diff --git a/openmc/deplete/results.py b/openmc/deplete/results.py
index adb0d3dbc04..c97de7bec56 100644
--- a/openmc/deplete/results.py
+++ b/openmc/deplete/results.py
@@ -103,7 +103,8 @@ def get_activity(
         mat: Material | str,
         units: str = "Bq/cm3",
         by_nuclide: bool = False,
-        volume: float | None = None
+        volume: float | None = None,
+        chain=None
     ) -> tuple[np.ndarray, np.ndarray | list[dict]]:
         """Get activity of material over time.
 
@@ -122,6 +123,14 @@ def get_activity(
         volume : float, optional
             Volume of the material. If not passed, defaults to using the
             :attr:`Material.volume` attribute.
+        chain : openmc.deplete.Chain or PathLike, optional
+            Depletion chain to use for half-life values. If provided, half-life
+            values from the chain are preferred over the default ENDF/B-VIII.0
+            values. Can be a Chain object or path to a chain XML file. For
+            nuclides not in the chain, the default values are used as a
+            fallback.
+
+            .. versionadded:: 0.15.1
 
         Returns
         -------
@@ -133,6 +142,8 @@ def get_activity(
             by_nuclide = True.
 
         """
+        from openmc.deplete import Chain
+
         if isinstance(mat, Material):
             mat_id = str(mat.id)
         elif isinstance(mat, str):
@@ -140,6 +151,9 @@ def get_activity(
         else:
             raise TypeError('mat should be of type openmc.Material or str')
 
+        if chain is not None and not isinstance(chain, Chain):
+            chain = Chain.from_xml(chain)
+
         times = np.empty_like(self, dtype=float)
         if by_nuclide:
             activities = [None] * len(self)
@@ -149,7 +163,8 @@ def get_activity(
         # Evaluate activity for each depletion time
         for i, result in enumerate(self):
             times[i] = result.time[0]
-            activities[i] = result.get_material(mat_id).get_activity(units, by_nuclide, volume)
+            activities[i] = result.get_material(mat_id).get_activity(
+                units, by_nuclide, volume, chain=chain)
 
         return times, activities
 
diff --git a/openmc/material.py b/openmc/material.py
index eded9c3faa6..ece2af8cecf 100644
--- a/openmc/material.py
+++ b/openmc/material.py
@@ -1386,7 +1386,9 @@ def get_element_atom_densities(self, element: str | None = None) -> dict[str, fl
 
 
     def get_activity(self, units: str = 'Bq/cm3', by_nuclide: bool = False,
-                     volume: float | None = None) -> dict[str, float] | float:
+                     volume: float | None = None,
+                     chain=None
+                     ) -> dict[str, float] | float:
         """Return the activity of the material or each nuclide within.
 
         .. versionadded:: 0.13.1
@@ -1405,6 +1407,13 @@ def get_activity(self, units: str = 'Bq/cm3', by_nuclide: bool = False,
             :attr:`Material.volume` attribute.
 
             .. versionadded:: 0.13.3
+        chain : openmc.deplete.Chain, optional
+            Depletion chain to use for half-life values. If provided, half-life
+            values from the chain are preferred over the default ENDF/B-VIII.0
+            values. For nuclides not in the chain, the default values are used
+            as a fallback.
+
+            .. versionadded:: 0.15.1
 
         Returns
         -------
@@ -1413,6 +1422,7 @@ def get_activity(self, units: str = 'Bq/cm3', by_nuclide: bool = False,
             names and values are activity is returned. Otherwise the activity
             of the material is returned as a float.
         """
+        import math
 
         cv.check_value('units', units, {'Bq', 'Bq/g', 'Bq/kg', 'Bq/cm3', 'Bq/m3', 'Ci', 'Ci/m3'})
         cv.check_type('by_nuclide', by_nuclide, bool)
@@ -1438,9 +1448,18 @@ def get_activity(self, units: str = 'Bq/cm3', by_nuclide: bool = False,
         elif units == 'Ci/m3':
             multiplier = 1e6 / _BECQUEREL_PER_CURIE
 
+        chain_nuclides = {}
+        if chain is not None:
+            for nuc in chain.nuclides:
+                chain_nuclides[nuc.name] = nuc.half_life
+
         activity = {}
         for nuclide, atoms_per_bcm in self.get_nuclide_atom_densities().items():
-            inv_seconds = openmc.data.decay_constant(nuclide)
+            if nuclide in chain_nuclides and chain_nuclides[nuclide] is not None:
+                t = chain_nuclides[nuclide]
+                inv_seconds = math.log(2) / t if t > 0.0 else 0.0
+            else:
+                inv_seconds = openmc.data.decay_constant(nuclide)
             activity[nuclide] = inv_seconds * 1e24 * atoms_per_bcm * multiplier
 
         return activity if by_nuclide else sum(activity.values())