15.7: Fission, Fusion, and Nuclear Decay

Describe the physical properties that constrain the behavior of interacting nuclei, subatomic particles, and nucleons.

• The strong force is exerted at nuclear scales and dominates the interactions of nucleons.

• Possible nuclear reactions are constrained by the law of conservation of nucleon number.

• The behavior of the constituent particles of a nuclear reaction are constrained by laws of conservation of energy, energy- mass equivalence, and conservation of momentum.

• For all nuclear reactions, mass and energy may be exchanged due to mass-energy equivalence.

• Energy may be released in nuclear processes in the form of kinetic energy of the products or as photons.

• Nuclear fusion is the process by which two or more smaller nuclei combine to form a larger nucleus and subatomic particles.

• Nuclear fission is the process by which the nucleus of an atom splits into two or more smaller nuclei and subatomic particles.

• Nuclear fission may occur spontaneously or may require an energy input to occur, depending on the binding energy of the nucleus.

Describe the radioactive decay of a given sample of material consisting of a finite number of nuclei.

Radioactive decay is the spontaneous fission of an atomic nucleus.

• The time at which an individual nucleus undergoes radioactive decay is indeterminable, but decay rates can be described using probability.

• The half-life of a radioactive material is the time for half of the initial number of radioactive nuclei to spontaneously decay.

• A material’s half-life may be used to predict the number of nuclei remaining in a sample after a period of time, or the age of a material if the initial amount of material is known.

• Different unstable elements and isotopes have vastly different half-lives, ranging from fractions of a second to billions of years.