Nuclear Energy

Nuclear Energy

High School

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Learning Objectives

• Define nuclear fission and fusion and describe the key differences between them.

• Identify and describe the four main types of radioactive decay.

• Analyze the main benefits and adverse effects of using nuclear energy.

• Explain how stars form different elements through the process of nucleosynthesis.

Key Vocabulary

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Isotopes

Atoms of the same element with different numbers of neutrons and different atomic masses.

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Half-life

The specific time it takes for half the radioactive atoms in a sample to decay.

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Nuclear Fission

The process of splitting a larger, unstable atomic nucleus into two or more smaller nuclei.

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Nuclear Fusion

The process where two or more smaller atomic nuclei combine to form a single heavier nucleus.

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Nucleosynthesis

The cosmic process of creating new atomic nuclei from pre-existing nucleons, primarily within stars.

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The Atom and Its Isotopes

The Atom

• The nucleus contains positively charged protons and neutrons, which have no charge at all.

• An element's identity is defined by its atomic number, which is the number of protons.

• Negatively charged electrons are particles that orbit around the outside of the atomic nucleus.

Isotopes

• Isotopes are versions of an element with the same number of protons but different neutrons.

• This difference in neutron count results in a different atomic mass for each isotope.

• For example, Uranium-235 is an isotope of the element uranium with a unique mass.

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Solved Example 1
Uranium-235 is a common isotope used in nuclear reactors. If the element uranium has an atomic number of 92, how many neutrons are in an atom of Uranium-235?

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Step 1: Analyze and Sketch the Problem

• Goal: Find the number of neutrons in an atom of Uranium-235.

• Knowns: The atomic mass is 235 and the atomic number is 92.

• Unknown: The number of neutrons.

• Formula: Number of Neutrons = Atomic Mass - Atomic Number.

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Solved Example 1
Uranium-235 is a common isotope used in nuclear reactors. If the element uranium has an atomic number of 92, how many neutrons are in an atom of Uranium-235?

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Step 2: Solve for the Unknown

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Solved Example 1
Uranium-235 is a common isotope used in nuclear reactors. If the element uranium has an atomic number of 92, how many neutrons are in an atom of Uranium-235?

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Step 3: Evaluate the Answer

• To check the answer, add the number of neutrons to the atomic number: 143 neutrons + 92 protons = 235.

• The result equals the atomic mass, so the calculation is correct. An atom of Uranium-235 has 143 neutrons.

Multiple Choice

What is the primary difference between isotopes of the same element?

• The number of protons in the nucleus.

• The number of electrons orbiting the nucleus.

• The number of neutrons in the nucleus.

• The overall charge of the atom.

Types of Radioactive Decay

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Alpha (α) Decay

• The nucleus releases a particle called an alpha particle.

• This particle consists of two protons and two neutrons.

• It is identical to the nucleus of a helium atom.

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Beta (β) Decay

• A neutron in the nucleus turns into a proton.

• An electron, also known as a beta particle, is emitted.

• The atom's atomic number increases by one during this process.

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Gamma (γ) Decay

• The nucleus releases energy in the form of gamma rays.

• This occurs when the nucleus is in an excited state.

• The atom's composition of protons and neutrons remains unchanged.

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Solved Example 2
A sample of Carbon-14 has a half-life of 5,730 years. If you start with a 100-gram sample, how much Carbon-14 will remain after 17,190 years?

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Step 1: Analyze and Sketch the Problem

• Goal: Determine the amount of Carbon-14 remaining after a certain time.

• Knowns: Initial amount = 100 g; Half-life = 5,730 years; Total time = 17,190 years.

• Unknown: Final amount of Carbon-14.

• Formula: The amount of substance is halved for each half-life that passes.

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Solved Example 2
A sample of Carbon-14 has a half-life of 5,730 years. If you start with a 100-gram sample, how much Carbon-14 will remain after 17,190 years?

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Step 2: Solve for the Unknown

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Solved Example 2
A sample of Carbon-14 has a half-life of 5,730 years. If you start with a 100-gram sample, how much Carbon-14 will remain after 17,190 years?

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Step 3: Evaluate the Answer

Multiple Choice

Which type of radioactive decay involves a neutron transforming into a proton, causing the emission of an electron?

• Beta Minus Decay

• Beta Plus Decay

• Gamma Decay

• Alpha Decay

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Nuclear Fission vs. Nuclear Fusion

Nuclear Fission

• This is the process of splitting a large atomic nucleus, like uranium-235, into smaller parts.

• The nucleus absorbs a neutron, becomes unstable, and splits, releasing a large amount of energy.

• This process releases more neutrons, which can create a chain reaction in nuclear power plants.

Nuclear Fusion

• This is the process of joining two or more lighter nuclei, such as hydrogen, into a heavier nucleus.

• This reaction releases immense amounts of energy and is the process that powers the sun and stars.

• For fusion to release energy, the elements involved must be lighter than iron on the periodic table.

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Solved Example 3
In the fission of Uranium-235, the nucleus absorbs a neutron and splits into Barium-141, Krypton-92, and 3 new neutrons. Given the atomic numbers of U (92), Ba (56), and Kr (36), is the total atomic number conserved?

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Step 1: Analyze and Sketch the Problem

• Goal: Determine if the total atomic number is conserved in the fission reaction.

• Knowns: Reactants: Uranium-235 (Atomic number = 92) and 1 neutron (Atomic number = 0). Products: Barium-141 (Atomic number = 56), Krypton-92 (Atomic number = 36), and 3 neutrons (Atomic number = 0).

• Unknown: Whether the total atomic number is conserved.

• Formula: Conservation of atomic number means Total Atomic Number of Reactants = Total Atomic Number of Products.

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Solved Example 3
In the fission of Uranium-235, the nucleus absorbs a neutron and splits into Barium-141, Krypton-92, and 3 new neutrons. Given the atomic numbers of U (92), Ba (56), and Kr (36), is the total atomic number conserved?

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Step 2: Solve for the Unknown

• Calculate the total atomic number of the reactants: 92 (from U) + 0 (from one neutron) = 92.

• Calculate the total atomic number of the products: 56 (from Ba) + 36 (from Kr) + (3 × 0) (from three neutrons) = 92. The total atomic number of the reactants (92) is equal to the total atomic number of the products (92).

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Solved Example 3
In the fission of Uranium-235, the nucleus absorbs a neutron and splits into Barium-141, Krypton-92, and 3 new neutrons. Given the atomic numbers of U (92), Ba (56), and Kr (36), is the total atomic number conserved?

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Step 3: Evaluate the Answer

• The calculation shows that the sum of the atomic numbers on both sides of the nuclear equation is equal.

• This confirms that the atomic number, and therefore the number of protons, is conserved during this nuclear fission reaction, which is a fundamental principle. The answer is correct.

Multiple Choice

Which statement accurately contrasts nuclear fission and fusion?

• Fission only occurs naturally in stars, while fusion is used in power plants.

• Fission splits large nuclei, while fusion combines light nuclei.

• Fission combines light nuclei, while fusion splits large nuclei.

• Fission releases less energy than burning coal, while fusion releases more.

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The Cosmic Forge: How Stars Create Elements

• The Sun's energy is from nuclear fusion, creating helium from hydrogen nuclei.

• ​All elements form through nucleosynthesis, a process starting after the Big Bang.

• A star’s core must reach 15,000,000°C to fuse atoms into new elements.

• Red supergiants forge elements heavier than iron during a supernova explosion.

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Solved Example 4
Uranium-235 (U-235) has an atomic number of 92. Determine the number of protons, neutrons, and electrons in one neutral atom of this isotope.

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Step 1: Analyze and Sketch the Problem

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Solved Example 4
Uranium-235 (U-235) has an atomic number of 92. Determine the number of protons, neutrons, and electrons in one neutral atom of this isotope.

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Step 2: Solve for the Unknown

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Solved Example 4
Uranium-235 (U-235) has an atomic number of 92. Determine the number of protons, neutrons, and electrons in one neutral atom of this isotope.

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Step 3: Evaluate the Answer

• The neutral Uranium-235 atom has 92 protons, 143 neutrons, and 92 electrons.

• Verification: The sum of protons and neutrons is 92 + 143 = 235, which correctly matches the mass number. The answer is consistent with the definitions of atomic number and mass number.

Multiple Choice

What is the process that uses nuclear fusion to create elements inside stars?

• Radioactive decay

• Nucleosynthesis

• Nuclear fission

• A chemical reaction

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Benefits and Drawbacks of Nuclear Energy

Benefits

• ​Nuclear power is a concentrated energy source that produces very little greenhouse gas emissions.

• ​​It provides a reliable alternative to fossil fuels for generating electricity for many countries.

• ​It is used to produce ionizing radiation for both medical and industrial purposes.

Drawbacks

• ​Fission creates dangerous nuclear waste that remains toxic for thousands of years.

• ​​Nuclear plants are very expensive to build and have a low net energy yield.

• ​There is a significant risk of accidents, such as a core meltdown.

Multiple Choice

According to the text, what is a primary benefit of nuclear power plants compared to fossil-fuel plants?

• They produce no dangerous waste.

• They release very little greenhouse gases.

• They have a high net energy yield.

• They are inexpensive to build.

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Common Misconceptions

Misconception	Correction
Nuclear power plants are the same as nuclear bombs.	Power plants use controlled reactions, while bombs use uncontrolled ones.
Nuclear power produces significant greenhouse gases.	Nuclear plants release very few greenhouse gases compared to fossil fuels.
Fission and fusion are the same process.	Fission splits large atoms, while fusion joins small atoms together.
A fusion reactor can have a meltdown.	Fusion reactions are not chain reactions and will stop if disturbed.

Multiple Choice

How do the changes in atomic particles differ between beta minus and beta plus decay?

• In beta minus, a neutron becomes a proton; in beta plus, a proton becomes a neutron.

• In beta minus, the atomic number decreases; in beta plus, it increases.

• In beta minus, an alpha particle is emitted; in beta plus, a positron is emitted.

• In beta minus, a proton becomes a neutron; in beta plus, a neutron becomes a proton.

Multiple Choice

Why is Uranium-235, a large atomic nucleus, more suitable for nuclear fission in a power plant than a light element like Helium?

• Because lighter elements cannot release energy through nuclear reactions.

• Because Helium is used in fusion, which is a safer process.

• Because Uranium-235 is less radioactive than Helium.

• Because fission is the process of splitting large nuclei, and U-235 can sustain a chain reaction.

Multiple Choice

Based on the principles of nucleosynthesis, what would be the primary consequence for the universe if no star could ever explode in a supernova?

• Elements heavier than iron would not be formed or distributed throughout the universe.

• Only the element hydrogen would exist in the universe.

• Stars would produce heavier elements at a much faster rate.

• The process of nuclear fusion in star cores would cease to happen.

Multiple Choice

A nation wants to develop a nuclear energy program with the highest priority on fuel abundance and a low risk of materials being used for weapons. Analyze which technology, fission or fusion, would be the better choice.

• Fusion, because its fuel is abundant and it does not use materials that can be easily weaponized.

• Fusion, because it releases less energy and is therefore easier to control.

• Fission, because it produces waste that can be re-used in other reactors.

• Fission, because the technology is already well-established and used in power plants worldwide.

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Summary

• Unstable nuclei undergo radioactive decay (alpha, beta, gamma) to become stable.

• Nuclear fission splits large nuclei for electricity; fusion combines light nuclei, powering stars.

• Elements heavier than hydrogen are created by nucleosynthesis in stars and supernovae.

• Nuclear energy is low-emission but has challenges like radioactive waste and accidents.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4