diff --git a/docs/source/pythonapi/data.rst b/docs/source/pythonapi/data.rst
index 471be43d8..a07fa9bc3 100644
--- a/docs/source/pythonapi/data.rst
+++ b/docs/source/pythonapi/data.rst
@@ -24,7 +24,6 @@ and product yields.
     FissionProductYields
     WindowedMultipole
     ProbabilityTables
-    AtomicRepresentation
 
 The following classes are used for storing atomic data (incident photon cross
 sections, atomic relaxation):
@@ -65,11 +64,11 @@ Core Functions
     dose_coefficients
     gnd_name
     isotopes
+    kalbach_slope
     linearize
     thin
     water_density
     zam
-    return_kalbach_slope
 
 One-dimensional Functions
 -------------------------
diff --git a/openmc/data/kalbach_mann.py b/openmc/data/kalbach_mann.py
index 4c6b89e41..10c002234 100644
--- a/openmc/data/kalbach_mann.py
+++ b/openmc/data/kalbach_mann.py
@@ -13,7 +13,7 @@ from .data import EV_PER_MEV
 from .endf import get_list_record, get_tab2_record
 
 
-class AtomicRepresentation(EqualityMixin):
+class _AtomicRepresentation(EqualityMixin):
     """Atomic representation of an isotope or a particle.
 
     Parameters
@@ -56,20 +56,20 @@ class AtomicRepresentation(EqualityMixin):
         self._a = a
 
     def __add__(self, other):
-        """Adds two AtomicRepresentations.
+        """Adds two _AtomicRepresentations.
 
         """
         z = self.z + other.z
         a = self.a + other.a
-        return AtomicRepresentation(z=z, a=a)
+        return _AtomicRepresentation(z=z, a=a)
 
     def __sub__(self, other):
-        """Substracts two AtomicRepresentations.
+        """Substracts two _AtomicRepresentations.
 
         """
         z = self.z - other.z
         a = self.a - other.a
-        return AtomicRepresentation(z=z, a=a)
+        return _AtomicRepresentation(z=z, a=a)
 
     @property
     def a(self):
@@ -89,7 +89,7 @@ class AtomicRepresentation(EqualityMixin):
 
     @classmethod
     def from_za(cls, za):
-        """Instantiates an AtomicRepresentation from a ZA identifier.
+        """Instantiate an _AtomicRepresentation from a ZA identifier.
 
         Parameters
         ----------
@@ -99,7 +99,7 @@ class AtomicRepresentation(EqualityMixin):
 
         Returns
         -------
-        AtomicRepresentation
+        _AtomicRepresentation
             Atomic representation of the isotope/particle
 
         """
@@ -115,11 +115,11 @@ def _separation_energy(compound, nucleus, particle):
 
     Parameters
     ----------
-    compound : AtomicRepresentation
+    compound : _AtomicRepresentation
         Atomic representation of the compound (C)
-    nucleus : AtomicRepresentation
+    nucleus : _AtomicRepresentation
         Atomic representation of the nucleus (A or B)
-    particle : AtomicRepresentation
+    particle : _AtomicRepresentation
         Atomic representation of the particle (a or b)
 
     Returns
@@ -219,9 +219,9 @@ def kalbach_slope(energy_projectile, energy_emitted, za_projectile,
     if za_target == 6000:
         za_target = 6012
 
-    projectile = AtomicRepresentation.from_za(za_projectile)
-    emitted = AtomicRepresentation.from_za(za_emitted)
-    target = AtomicRepresentation.from_za(za_target)
+    projectile = _AtomicRepresentation.from_za(za_projectile)
+    emitted = _AtomicRepresentation.from_za(za_emitted)
+    target = _AtomicRepresentation.from_za(za_target)
     compound = projectile + target
     residual = compound - emitted
 
diff --git a/tests/unit_tests/test_data_kalbach_mann.py b/tests/unit_tests/test_data_kalbach_mann.py
index bd540addb..2a579b703 100644
--- a/tests/unit_tests/test_data_kalbach_mann.py
+++ b/tests/unit_tests/test_data_kalbach_mann.py
@@ -6,8 +6,7 @@ import pytest
 import numpy as np
 
 from openmc.data import IncidentNeutron
-from openmc.data import AtomicRepresentation
-from openmc.data.kalbach_mann import _separation_energy
+from openmc.data.kalbach_mann import _separation_energy, _AtomicRepresentation
 from openmc.data import kalbach_slope
 from openmc.data import KalbachMann
 
@@ -17,43 +16,43 @@ from . import needs_njoy
 @pytest.fixture(scope='module')
 def neutron():
     """Neutron AtomicRepresentation."""
-    return AtomicRepresentation(z=0, a=1)
+    return _AtomicRepresentation(z=0, a=1)
 
 
 @pytest.fixture(scope='module')
 def triton():
     """Triton AtomicRepresentation."""
-    return AtomicRepresentation(z=1, a=3)
+    return _AtomicRepresentation(z=1, a=3)
 
 
 @pytest.fixture(scope='module')
 def b10():
     """B10 AtomicRepresentation."""
-    return AtomicRepresentation(z=5, a=10)
+    return _AtomicRepresentation(z=5, a=10)
 
 
 @pytest.fixture(scope='module')
 def c12():
     """C12 AtomicRepresentation."""
-    return AtomicRepresentation(z=6, a=12)
+    return _AtomicRepresentation(z=6, a=12)
 
 
 @pytest.fixture(scope='module')
 def c13():
     """C13 AtomicRepresentation."""
-    return AtomicRepresentation(z=6, a=13)
+    return _AtomicRepresentation(z=6, a=13)
 
 
 @pytest.fixture(scope='module')
 def na23():
     """Na23 AtomicRepresentation."""
-    return AtomicRepresentation(z=11, a=23)
+    return _AtomicRepresentation(z=11, a=23)
 
 
 def test_atomic_representation(neutron, triton, b10, c12, c13, na23):
     """Test the AtomicRepresentation class."""
     # Test instantiation from_za
-    assert b10 == AtomicRepresentation.from_za(5010)
+    assert b10 == _AtomicRepresentation.from_za(5010)
 
     # Test addition
     assert c13 + b10 == na23
@@ -76,13 +75,13 @@ def test_atomic_representation(neutron, triton, b10, c12, c13, na23):
 
     # Test instanciation errors
     with pytest.raises(ValueError):
-        AtomicRepresentation(z=5, a=1)
+        _AtomicRepresentation(z=5, a=1)
     with pytest.raises(ValueError):
-        AtomicRepresentation(z=-1, a=1)
+        _AtomicRepresentation(z=-1, a=1)
     with pytest.raises(ValueError):
-        AtomicRepresentation(z=5, a=0)
+        _AtomicRepresentation(z=5, a=0)
     with pytest.raises(ValueError):
-        AtomicRepresentation(z=5, a=-2)
+        _AtomicRepresentation(z=5, a=-2)
     with pytest.raises(ValueError):
         neutron - triton