Alpha Emission
The three most common types of radioactive emission are alpha, beta and gamma. For example, when a Uranium238 nucleus decays, it produces a Thorium234 nucleus and a Helium4 nucleus. That Helium4 nucleus is called an alpha particle(
α).








238 


234 


4 


U 
→ 

Th 
+ 

He 
92 


90 


2 


There are two important things to note here:
 The sum of the isotopic masses (top numbers) are equal on both sides of the equation. [238 =234 + 4]
 The sum of the atomic numbers (the bottom numbers) also are equal on both sides of the equation. [92 = 90 + 2]