Nuclear Fission and Fusion

Chapter 7.2Mrs. Chilton

Nuclear Stability

• Some elements have isotopes that are stable, while others are unstable and radioactive– Example: C-12 -> stable– C-14 -> unstable, radioactive, gives off beta

particles

• Depends on nuclear forces holding nucleus together

Strong Nuclear Force

• How do like charges act?

• They repel!

• So, why does the nucleus with so many p+ stay together?

• Strong nuclear force – stronger force than electric repulsion, but only over a short distance

Neutrons & Stability

• Neutrons add to the stability of a nucleus

• They have no charge, so they do not repel

• Too many or too few neutrons leads to decay

• All nuclei with 83 or more protons are unstable

Fission

• When a nucleus splits into two or more smaller fragments

• Neutrons and energy are released

Fission -> Chain Reaction

• One neutron can split the nucleus of an atom

• As that nucleus undergoes fission, it releases more neutrons which can strike nearby atoms, causing them to split

• This can cause a chain reaction

Nuclear Chain Reaction

Uncontrolled chain reactions

• This principle is used in nuclear bombs• Two or more masses of U-235 are

contained in bomb surrounded by powerful explosive

• When detonated, fission chain reaction occurs releasing LARGE amount of energy which causes devastation to environment and life forms

• Fortunately, concentration of U-235 in nature is too low to start a chain reaction, most is more stable form of U-238

Controlled Chain Reaction

• Not all neutrons released in a fission reaction succeed in triggering fission reaction

• Materials that absorb neutrons can be used to slow chain reaction

• Concept is used in nuclear power plants to generate energy

Nuclear Reactor

Fusion

• Energy can also be obtained when two lighter nuclei fuse together to form a larger nucleus

• In stars, including our sun, energy is produced when hydrogen nuclei undergo fusion and release TREMENDOUS amounts of energy

Fusion in the Sun

• Multi-step process where two different isotopes of hydrogen fuse together to form a helium nucleus and energy in form of gamma rays

Dangers of Nuclear Radiation

• Changes structure of hemoglobin

• Changes structure of macromolecules in body – health is affected

• Particles ingested through food can damage linings of organs

• Destroys bone marrow• Lung cancer (Radon gas)• Genetic mutation

Beneficial Uses of Nuclear Radiation

• Smoke alarms –produce alpha particles to create electric current

• Controlled doses are used to treat some cancers – beams of gamma rays

• Radioactive tracers

• Nuclear power – much less pollution, more efficient (waste must be dealt with, though)

Radioactive Waste Disposal