diff --git a/src/pg_rad/isotopes/presets.py b/src/pg_rad/isotopes/presets.py
index 9d07a65..d8135d6 100644
--- a/src/pg_rad/isotopes/presets.py
+++ b/src/pg_rad/isotopes/presets.py
@@ -3,7 +3,7 @@ from .isotope import Isotope
 
 class CS137(Isotope):
     def __init__(self):
-        super.__init__(
+        super().__init__(
             name="Cs-137",
             E=661.66,
             b=0.851
diff --git a/src/pg_rad/objects/sources.py b/src/pg_rad/objects/sources.py
index ee47509..9361f1f 100644
--- a/src/pg_rad/objects/sources.py
+++ b/src/pg_rad/objects/sources.py
@@ -11,22 +11,23 @@ class PointSource(BaseObject):
 
     def __init__(
             self,
-            pos: tuple,
             activity: int,
             isotope: Isotope,
+            pos: tuple[float, float, float] = (0, 0, 0),
             name: str | None = None,
-            color: str = "red"):
+            color: str = 'red'
+            ):
         """A point source.
 
         Args:
-            pos (tuple): a position vector of length 3 (x,y,z).
             activity (int): Activity A in MBq.
             isotope (Isotope): The isotope.
-            name (str | None, optional): Can give the source a unique name.
-            Defaults to None, making the name sequential.
-            (Source-1, Source-2, etc.).
-            color (str, optional): Matplotlib compatible color string.
-            Defaults to "red".
+            pos (tuple[float, float, float], optional):
+                Position of the PointSource.
+            name (str, optional): Can give the source a unique name.
+                If not provided, point sources are sequentially
+                named: Source1, Source2, ...
+            color (str, optional): Matplotlib compatible color string
         """
 
         self.id = PointSource._id_counter