Nuclear Fusion AN INTRODUCTION TO THE HYDROGEN BURNING

Nuclear Fusion AN INTRODUCTION TO THE HYDROGEN BURNING AND THE ALPHA PARTICLE

Subatomic Particles The subatomic particles combine to form an atom Proton: Positively charged, one mass unit, located in nucleus Neutron Neutral, one mass unit, located in nucleus Electron Negatively charged, no mass, located in electron cloud (surrounding nucleus)

Basics of an Atomic Nucleus An atom is defined by the number of protons it has in its nucleus Atomic Mass (A) Atomic Number: Number of protons Atomic Mass: Sum of neutrons and protons 1 1 H Hydrogen Nucleus Atomic Number: 1 Atomic Mass: 1 Atomic number (Z) +

Main Sequence Stars Main sequence stars are like our sun They have an balance between outward thermal pressure and inward gravitational pressure. This balance is called hydrostatic equilibrium. The outward push from thermal pressure The inward push from gravity The pressure is generated from thermal energy from nuclear fusion in the core

Hydrogen Burning The process of hydrogen burning occurs in the core of stars It is also called ‘proton-proton fusion. ” It consists of 3 steps. It requires temperature of 10 million K or hotter This process is the longest stage in a star’s life

Proton – Proton Fusion Step 1 Fusion: the combining of 2 or more atoms to create a new, larger atom Hydrogen burning, or proton-proton fusion, occurs in main sequence stars. 1 1 1 Forms a Deteurium atom (“heavy Hydrogen atom”) Atomic Number: 1 Atomic Mass: 2 1 H H + + + n 2 1 H

Deuterium nucleus combines with a regular Hydrogen nucleus Forms a Helium-3 nucleus: Atomic number: 2 Atomic mass: 3 Proton-Proton Fusion Step 2 + 2 H n 1 1 + H 1 3 + He + 2 n

Two Helium-3 nuclei combine to form a Helium-4 nucleus The Helium-4 nucleus: Atomic number: 2 Atomic mass: 4 This is also known as an alpha particle Proton-Proton Fusion Step 3 3 + He + 2 n + 4 2 He + n 3 + He + 2 n +

The 4 He atom is known as an alpha particle It is one of the building blocks of larger elements Alpha Particle 4 + He n + 2 n

Summary Atoms are made of subatomic particles. These consist of protons, neutrons and electrons. An atom is described by its atomic number and atomic mass. The gravitational pressure in stars is balanced by an outward thermal pressure. The energy is generated by nuclear fusion in stars. Hydrogen burning is a nuclear fusion process which results in the formation of alpha particles (Helium-4 nuclei). This occurs through proton-proton fusion, which is a 3 -step process.