Unit 18

Transmutation, Fission, and Fusion

Fusion• The combination of two smaller

atoms into one larger one.

Hydrogen

HydrogenHelium

Lithium

Beryllium

Fusion Makes Larger Elements

Fusion is Hard!• Because the protons repel each other, getting two

atoms close enough to fuse is hard.• It takes temperatures approaching 10 million degrees

to have them travel fast enough to overcome the electrostatic repulsion

Strong Nuclear Force

• The strong nuclear force is the force that holds the nucleus together.

• All Nucleons are attracted to each other.• Because + protons repel each other

(electromagnetic force), the presence of neutrons helps bind the nucleus together.

++

Electromagnetic Force

Strong Nuclear Force

+N

Strong Nuclear Force

NN

Strong Nuclear Force

Strong Nuclear Force• It only acts within the nucleus• Fusion can only occur if protons are brought

within the nucleus.• One approach is to shoot particles at each

other at near the speed of light.

Fusion Releases Energy• When fusion occurs, some of the matter is

converted to energy and that energy is released as heat.

Stars are Element Makers• Medium stars like our sun mostly convert Hydrogen to Helium.

• Later, it will convert Helium to Carbon.

• Giant stars can fuse higher atoms to larger elements.

The Interior of a Giant Star

Super Nova

• Brighter than a galaxy!• Shockwave spreads heavier

elements across galaxy• Those heavy elements

condense into planets

Human Induced Fusion

• Hydrogen Bomb

Fission

• When an atom splits into two smaller atoms.

• The release of the strong nuclear force releases energy in the form of heat.

Nuclear Power

• Controlled fission reactions can generate heat to boil water to energy electricity.

Atomic Bomb

• Uncontrolled fission reactions

Critical Mass

• Fission can only occur as a chain reaction, if you have the critical mass.

• Otherwise, the neutrons simply run out of material to split.

How to Make The Bomb

• Have two uncritical masses separated from each other.

• Using dynamite, you can launch the masses together beginning the nuclear reaction.

Nuclear Transmutation• New elements or isotopes can be created by

adding particles to elements or splitting atoms.• These are generally done using particle

accelerators.• These speed particles at each other near the

speed of light to overcome electrostatic repulsion.

Nuclear Transmutation• Most of the “artificial elements” have been

created by adding particles to large atoms.

Cf249

98

C12

6

Rf257

104

4NCalifornium Carbon Rutherfordium

Particle Accelerators

Magnets Are Used to Move Particles

Particle Collider

Collision of Gold Particles

How to Detect Particles