Nuclear Reactions Quiz

Week Eleven: Lesson Three - Energy Changes in Nuclear Reactions

• Nuclear reactions differ significantly from chemical reactions.
• Elements change during nuclear reactions, while electrons change less frequently in nuclear reactions.
• Nuclear reactions release substantial energy, causing mass changes.
• Reaction rates aren't affected by temperature or catalysts.

Lesson Objectives

• Differentiate between nuclear and chemical reactions.
• Understand various types of nuclear reactions.
• Calculate mass defect and binding energy.

Nuclear Reactions: Types

• Nuclear Fission: Large nuclei split into smaller, nearly equal parts, releasing energy. Spontaneous fission is rare; induced fission is more common. Typically, heavy nuclei are bombarded with neutrons.
• Example: U-235 absorbing a neutron to form unstable U-236, which rapidly fissions into smaller nuclei (e.g., xenon-140 and strontium-93) and releasing neutrons and energy (gamma radiation, too.)
• Nuclear Fusion: Light nuclei fuse into a heavier nucleus, releasing energy. An example is the fusion of hydrogen isotopes in the Sun and stars. Occurs at extremely high temperatures, necessary to overcome repulsion forces between positively charged nuclei.

Features of Nuclear Fission

• Fission products are radioactive.
• Excess neutrons are released.
• Neutrons can induce further fissions, creating a chain reaction.

Nuclear Fusion Features

• Mostly in the sun.
• Occurs at extremely high temperatures.
• Products are not radioactive.
• No material can withstand the temperatures needed to create sustained fusion and maintain it.
• Energy released is significantly greater than in fission.

Advantages of Fusion over Fission

• Easier to achieve (lesser repulsion between light nuclei)
• Easily accessible fuel (hydrogen isotopes).
• Less dangerous, due to less radioactive products.
• No chain reaction concerns.

Binding Energy

• Binding energy is the energy required to bring nucleons (protons and neutrons) together or to separate them.

• Binding energy is equivalent to the mass defect.

• Mass defect is the difference in mass between the sum of the separated nucleons and the resultant nucleus.

• Binding energy is from the forces holding the nucleus.

• Binding energy is calculated using E=mc². A mass difference results in energy release.

• Different nuclei have differing binding energies. In fission, large nucleus splits into smaller parts; the lower total mass of smaller nuclei after fission results in energy released.

• Fast neutrons must be slowed down (moderators such as graphite rods) for fission to happen. Excess neutrons are absorbed using boron rods.