diff --git a/src/pg_rad/isotopes/presets.py b/src/pg_rad/isotopes/presets.py
new file mode 100644
index 0000000..5b8224b
--- /dev/null
+++ b/src/pg_rad/isotopes/presets.py
@@ -0,0 +1,4 @@
+from .isotope import Isotope
+
+
+CS137 = Isotope("Cs-137", E=661.66, b=0.851)