diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 7bf86f03fb0d762f48174d710b757637e7fde617..f049ddc719c18f74bb25476d3d944ea1829fd113 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -461,5 +461,6 @@ python-examples:
     - cd ${CI_PROJECT_DIR}/python/examples
     - python3 particle_distribution.py --input-dir $EXAMPLE_SHOWER_DIR
     - python3 shower_profile.py --input-dir $EXAMPLE_SHOWER_DIR
+    - python3 first_interactions.py --input-dir $EXAMPLE_SHOWER_DIR
     - export EXAMPLE_RADIO_SHOWER_DIR=${CI_PROJECT_DIR}/build/build_examples/example_outputs/radio_em_shower_outputs
     - python3 radio_emission.py --input-dir $EXAMPLE_RADIO_SHOWER_DIR
diff --git a/python/corsika/io/outputs/interaction.py b/python/corsika/io/outputs/interaction.py
index 21a1b1d54650066d2d3e664238e8dc3f6286d154..956d1d75bfbdf5b8874fc73d018f56e561e427f6 100644
--- a/python/corsika/io/outputs/interaction.py
+++ b/python/corsika/io/outputs/interaction.py
@@ -36,9 +36,6 @@ class FirstInteraction(Particle):
         """
         Particle.__init__(self, prop_dict)
 
-        # need to define for momentum prop
-        self.px = self.py = self.pz = None
-
     def __repr__(self) -> str:
         """
         Return a string representation of this class.
diff --git a/python/corsika/io/outputs/primary.py b/python/corsika/io/outputs/primary.py
index d0105f1a0f9285a17e0d6d2acfe5afd56a044ce7..d5ee863cef4b8e7340b78605ce6c57872387f67b 100644
--- a/python/corsika/io/outputs/primary.py
+++ b/python/corsika/io/outputs/primary.py
@@ -34,6 +34,7 @@ class Particle(object):
         # need to define for position/direction functions
         self.x = self.y = self.z = None
         self.nx = self.ny = self.nz = None
+        self.px = self.py = self.pz = None
 
         # wrap the files of the dictionary so that there is a property
         # assigned to each value, i.e. print(my_primary.pdg)
diff --git a/python/examples/first_interactions.py b/python/examples/first_interactions.py
index d86d8d70dd7cbe21adad95ac6eed4d71b8dfa97a..25476eb80f7b5b1dbc1c453ce82c65579a9e3278 100644
--- a/python/examples/first_interactions.py
+++ b/python/examples/first_interactions.py
@@ -54,7 +54,6 @@ for ish, sh_id in enumerate(shower_ids):
     daughters = interactions[interactions["shower"] == sh_id]
 
     mother = projectiles[ish]
-    norm = np.sqrt(sum(np.array(mother.momentum) ** 2))  # total momentum
 
     print("Plotting shower", sh_id)
     print(mother)