diff --git a/302. NUCE 2100 - Fundamentals of Nuclear Engineering/2024-08-27 Introduction.md b/302. NUCE 2100 - Fundamentals of Nuclear Engineering/2024-08-27 Introduction.md
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--- a/302. NUCE 2100 - Fundamentals of Nuclear Engineering/2024-08-27 Introduction.md	
+++ b/302. NUCE 2100 - Fundamentals of Nuclear Engineering/2024-08-27 Introduction.md	
@@ -109,3 +109,27 @@ The chart of the nuclides is how we understand chains of decay, and what will tu
 Any process that releases energy is referred to as radioactive decay. 
 **Radionuclide** - an unstable nuclide that is going to decay.
 
+Types of radiation
+1. Electromagnetic - Energy transmitted as electromagnetic waves
+	1. radio, microwave, infrared, etc
+	2. Characterized by its frequency
+	3. wave-particle business
+	4. Photons!
+	5. Ionizing at the gamma / x ray range. 
+		1. gamma $\gamma$ rays are super high energy
+		2. They happen when atoms rearrange themselves. Excess energy is emitted as a gamma ray.
+2. Ionizing Radiation - Enough energy to remove one or more electrons from an atom
+
+# Doing Math
+## Nuclear Decay
+Decay is a random process.
+**Decay constant:**
+$$\lambda = \frac{\text{decay}}{\text{nucleus-second}}$$
+
+Activity is the amount of decays per second
+$N$ is the number of nuclei present. these are functions of time.
+**Activity:**
+$$ A(t) = \lambda N(t) $$
+$$N(t) = N(0) e^{-\lambda t}$$
+Half life is a derivative of activity:
+$$ t_{1/2} = \frac{0.693}{\lambda}$$ 
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