diff --git a/300s School/NUCE 2100 - Fundamentals of Nuclear Engineering/2024-09-17 Module 5 Nuclear Fission Basics.md b/300s School/NUCE 2100 - Fundamentals of Nuclear Engineering/2024-09-17 Module 5 Nuclear Fission Basics.md
index 52581436..b27154a8 100644
--- a/300s School/NUCE 2100 - Fundamentals of Nuclear Engineering/2024-09-17 Module 5 Nuclear Fission Basics.md	
+++ b/300s School/NUCE 2100 - Fundamentals of Nuclear Engineering/2024-09-17 Module 5 Nuclear Fission Basics.md	
@@ -36,3 +36,5 @@ Rate of increase = Production - absorbed - leakage
 $$k = \frac{\text{Number of neutrons in one generation}}{\text{Number of neutrons in preceding generation}}$$
 Measures how many neutrons produced by each neutron born.
 There are more formulas in the slides. K can be based on material properties
+## Energy Dependence
+Fission is most efficiently caused by thermal neutrons (energy < 1eV), but neutrons from fission are born at something like \>2MeV. 7 orders of magnitude reduction -- usually kinetic losses by neutrons colliding with things.