Nuclear Fusion and Fission

Going Nuclear!

•The source of our sun’s energy was a mystery for

a long time.

• In the 1920s, Arthur Eddington proposed hydrogen

fusion based on Einstein’s mass equivalence equation.

• Eddington also led an expedition to view the 1919

total solar eclipse which help confirm Einstein’s
theory of general relativity.

•Hydrogen is the most common element in the

universe.

•Stars form when clouds of hydrogen collapse

gravitationally.

• The gravitational forces provide enough heat and pressure to begin fusing

hydrogen nuclei together to produce helium.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

Draw

What is Einsteins mass equivalent equation?

Going Nuclear!

•Since the strong nuclear force is more powerful than electrostatic repulsion at the

nuclear scale, enormous energy is released when light nuclei are fused together.

• The nuclei must be forced close together against the electric force.
• Once close enough, the strong nuclear force overwhelms the electric force and the nuclei

crash together.

• The collision releases gamma

rays (light) and kinetic energy
(heat).

• This energy is convected to the

surface of the sun, where its
surface is ~6000K.

• This energy is transferred to the

solar system via electro-
magnetic radiation (light).

Solar fusion & nucleosynthesis

Theory of nucleosynthesis

Going Nuclear!

•In the core of the sun, hydrogen nuclei are fused

together into helium in the proton chain process.

• Two hydrogen-1 (lone protons) are fused into

hydrogen-2 after a positron is ejected (

decay) .

• Another hydrogen-1 is fused, producing helium-3 and

another gamma ray.

• Finally two helium-3 will fuse producing helium-4

and two new hydrogen-1 nuclei.
• These daughter nuclei have increased kinetic

energy and therefore higher temperature. Desmos

•The sun “burns” 600 million tons of hydrogen every

second.
• This produces 596 million tons of helium.

• Where did the other 4 million tons of mass go?

β+

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

Multiple Choice

In which process do hydrogen nuclei crash together?

• Helium chain reaction

• fission

• CNO Cyle

• Proton chain

Multiple Choice

What element would you expect from the fusion of H-3 and H-2

• H-5

• He-4

• He-5

• H-1

Going Nuclear!

•As a consequence of Einstein’s theory of special relativity, mass and energy are

equivalent.

• From the other perspective, this equation also tells

us what mass actually is.
• Mass is the total energy content of matter. More potential energy from the strong or electric force

becomes more mass in an element.

•It would require energy to pull helium nucleons apart

against the strong nuclear force to form hydrogen again.

• The energy “invested” into the nucleons by pulling them

apart is reflected in the mass.

• The binding energy of an atoms

is the amount of energy it would
take to separate nucleons.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

E = mc2

⟹

m =E

c2

Multiple Choice

What element would you expect from the fusion of He-3 and H-1

• Li-4

• Be-4

• He-4

• Li-5

Going Nuclear!

•The mass of a lone proton is 1.00728 amu.

The mass of a lone neutron is 1.00866 amu.

• All elements except hydrogen have nuclei

with less mass than sum of their parts.

• This missing mass is called mass defect.

•Iron-56 has the lowest energy “valley”

(or highest binding energy).

• It has the perfect balance between strong nuclear

force interactions of nucleons vs electrostatic
repulsions of protons.

•The fusion of light elements releases even more

energy that the fission of heavy elements.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

1
1H = 1.00783 amu

⟹

1.00783 amu per nucleon

2
1D = 2.01410 amu

⟹

1.00705 amu per nucleon

4
2He = 4.00260 amu

⟹

1.00065 amu per nucleon

56
26Fe = 55.93494 amu

⟹

0.99884 amu per nucleon

238

92U = 238.05079. amu

⟹

1.00021 amu per nucleon

Multiple Choice

A proton has a mass of 1.00783 amu in all atoms/elements

• True

• False

Multiple Choice

Which type of energy manifests itself as mass in an atom?

• Kinetic Energy

• Magnetic Energy

• Potential Energy

• Kinetic and Potential Energy

Going Nuclear!

•The stellar fuel cycle occurs as fusion combines lighter elements into heaver

elements in successive states.

•The first stage is fusion of hydrogen to produce helium as done in our sun.

•After burning through all the hydrogen in the core of a star, helium is fused to

produce beryllium, and then carbon.

• Low mass stars may not have the

gravitation power to follow the cycle
past this point.

• This will result in white dwarf star

(giant glowing diamond!)

•Higher mass stars will continue to fuse carbon,

oxygen, silicon, etc until the formation of iron-56.

• The stages of these stars will go through stages of red giant, super giant, and blue supergiant.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

Multiple Select

Which nuclei listed will release energy from Fusion with smaller nuclei?

• He-4

• P-239

• Mg-24

• U-235

• Th-231

Multiple Select

Which nuclei listed will release energy from Fission with larger nuclei?

• He-4

• P-239

• Mg-24

• U-235

• Th-231

Going Nuclear!

•The theory of nucleosynthesis holds that all of the elements in our solar system

were formed from previous generations of stars.

• High mass stars will burn through their stellar fuel cycle.
• Fusion releases energy until forming iron-56.
• When all nuclear fuel is consumed, the star will collapse

and then explode in a super nova.

• The force of the collapse and

explosion provides to energy
to fuse elements with masses
greater than 56.

• The material from the

supernova will condense into
new stars and begin the cycle
again.

• Fission releases energy stored

from a supernova.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

Remnants of Kepler’s supernova in 1604.

Going Nuclear!

•Since iron-56 has the lowest mass, this

explains why both fusion and fission can
release energy.

• Fusion of light elements releases energy from

the strong nuclear force attraction.

• Fission of heavy elements releases energy from

electric force repulsion.

Solar fusion & nucleosynthesis

Nuclear Fission & Fusion

Multiple Choice

What is the fusion product of Curium-245 and Carbon-12

• Nobelium-257

• Nobelium-256

• Uranium-256

• Uranium-257

Multiple Choice

What is the fusion product of Be-9 and Ne-21

• Silicon-30

• Silicon-28

• Aluminum-29

• Aluminum-30

Going Nuclear!

•Soon after the development of atomic (fission) weapons, fusion weapons (know as

thermonuclear or hydrogen bombs) were developed.

• Fusion weapons use high

explosives to power a fission
reaction that powers a fusion
reaction.

• Tritium (H-3) and deuterium (H-2)

are often used as the fusion fuel.

•Fusion power is currently being tested experimentally.

• The primary difficulty is containing the fusion process which

operates at temperatures in the range of billions of degrees.

• Confinement mechanisms include using

magnets or lasers to contain the reaction.

Fusion weapons & fusion power

Nuclear Fission & Fusion

Ivy Mike Detonation- 1 Nov 1952

Tokamat Containment

Open Ended

How are fission and fusion different? Explain your answer using examples.