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Section 24-3

Nuclear Fission

- Stability of elements is best around a mass

number of 60. - Atoms with a mass number greater than 60 tend to

gain stability by fragmenting. - The splitting of nuclei into fragments is known

as nuclear fission.

- Fission is accompanied with a very large release

of energy.

Section 24-3

Nuclear Fission

- Nuclear power plants use fission to produce

electricity by striking uranium-235 with neutrons.

Section 24-3

Nuclear Fission (cont.)

- Each fission of U-235 releases three additional

neutrons.

- Each of those neutrons can release three more

neutrons. - The self-sustaining process is called a chain

reaction. - http//glencoe.mcgraw-hill.com/sites/007874637x/st

udent_view0/chapter24/concepts_in_motion.html

Section 24-3

Nuclear Fission (cont.)

Section 24-3

Nuclear Fission (cont.)

- There must be sufficient mass to get the chain

reaction started. If not the neutrons escape

before striking other nuclei. - Without sufficient mass, neutrons escape from the

sample before starting a chain reaction.

- Samples with enough mass to sustain a chain

reaction are said to have critical mass. - Samples with mass that is much greater than the

critical mass have a reaction that escalates at a

violent level and can cause a nuclear explosion.

This is the supercritical mass.

Section 24-3

Nuclear Fission (cont.)

http//www.youtube.com/watch?vqybUFnY7Y8w

Section 24-3

Nuclear Reactors

- Nuclear fission produces the energy generated by

nuclear reactors.

- The fission within a reactor is started by a

neutron-emitting source and is stopped by

positioning the control rods to absorb virtually

all of the neutrons produced in the reaction.

Section 24-3

Nuclear Reactors (cont.)

- The reactor core contains a reflector that

reflects neutrons back into the core, where they

react with fuel rods.

- Nuclear reactors produce highly radioactive

nuclear waste. - Breeder reactors produce more fuel than they

consume.

Section 24-3

Nuclear Reactors (cont.)

Section 24-3

Nuclear Fusion

- It is possible to bind together two or more

lighter elements (mass number less than 60).

- The combining of atomic nuclei is called nuclear

fusion. - Nuclear fusion is capable of releasing very large

amounts of energy. - The sun is powered by the fusion of hydrogen

atoms to form helium atoms and a lot of energy.

Section 24-3

Nuclear Fusion (cont.)

- Fusion has several advantages over fission.

- Lightweight isotopes are abundant.
- Fusion products are not radioactive.
- However, fusion requires extremely high energies

to initiate and sustain a reaction.

Section 24-3

Nuclear Fusion (cont.)

- Fusion reactions are also known as thermonuclear

reactions.

- Many problems must be solved before nuclear

fusion is a practical energy source.

Section 24-3

Section 24.3 Assessment

Bombarding a nuclei with charged particle in

order to create new elements is called ____.

A. nuclear conversion B. nuclear decay

C. induced decay D. induced transmutation

- A
- B
- C
- D

Section 24-3

Section 24.3 Assessment

Thermonuclear reactions involve A. splitting

nuclei into smaller fragments B. fusing nuclei

together to form larger particles

C. bombarding nuclei with charged particles

D. generating electricity in a nuclear reactor

- A
- B
- C
- D