NUCLEAR PROCESSESFission & Fusion

FISSION VS. FUSION

FISSION VS. FUSION In nuclear fusion, two nuclei combine to

form a more massive nucleus. Fusion means the merging together of

different elements to make a new element.

In nuclear fission, a massive nucleus splits into two lighter nuclei. Fission means breaking something up into

parts.

MASS ENERGY EQUIVALENCE• In the nucleus the strong

interaction binds the nucleons tightly together.

• When nucleons are bound together by the strong interaction, their energy is reduced — they go into a low-energy state.

• The binding energy of a nucleus is the energy required to break up the nucleus into its individual protons and neutrons.

MASS ENERGY EQUIVALENCE

MASS DEFECT The law of conservation of mass says that mass

is never created or destroyed.

It is surprising that accurate measurements show that a bit of mass disappears when nuclei form from their individual nucleons: the mass of a nucleus is less than the sum of the

masses of the individual protons and neutrons that make up the nucleus.

This missing mass is called the mass defect

LAW OF CONSERVATION OF

MASS-ENERGY

Mass can be transformed into energy and energy can be transformed into mass.

This explains the mass defect: when nucleons are bound together, their energy is reduced, so their mass is also reduced.

The binding energy of a nucleus is the mass-energy equivalent of its mass defect.

MASS ENERGY EQUIVALENCEDetermine the mass-energy equivalent of 1.0 kg of gasoline.

NUCLEAR REACTIONS

NUCLEAR FISSION

Fission is the reaction in which a massive nucleus splits into two or more lighter nuclei.

1. Spontaneous Fission: Spontaneous fission occurs when an unstable isotope splits into two or more smaller nuclei without any external interaction.

It is only seen in nuclei with atomic mass numbers above 230 (elements near thorium).

Induced Fission: a nucleus absorbs a neutron, forming a highly unstable isotope that breaks up almost instantly into two lighter nuclei

NUCLEAR FISSIONThorium-230 decays to polonium-218 by three alpha decays. Write the equations for the reactions. Use a periodic table.

NUCLEAR FISSION

NUCLEAR FUSIONThe dominant fusion reaction in stars the size of our Sun or smaller is the proton-proton chain.

NUCLEAR FUSIONAnother form of fusion is neutron absorption.