The document discusses nuclear fusion in stars. It explains that hydrogen burning occurs through proton-proton fusion in main sequence stars like our Sun. This is a three step process where hydrogen nuclei fuse to form deuterium, then helium-3, and finally two helium-3 nuclei combine to form a stable helium-4 nucleus, known as an alpha particle. This nuclear fusion reaction is the primary source of energy in stars and the longest phase of their life cycle.

1. A n i n t r o d u c t i o n t o t h e h y d r o g e n b u r n i n g a n d t h e a l p h a
p a r t i c l e
Nuclear Fusion

2. 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)

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

4. 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
the thermal
energy from
nuclear fusion
in the core

5. 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

6. 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.
Forms a Deteurium
atom (“heavy
Hydrogen atom”)
Atomic Number: 1
Atomic Mass: 2
+
+
+
n
H
H
1
1
1
1
H
2
1

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

8. Proton-Proton Fusion
Step 3
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
He
2
+
n
+
He
2
3 +
n
+
3
He
2
4
+
n
+
n
+
+

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

10. 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.
Summary