Physics 001.002.017 Distinguishing Artificial Transmutation and Natural Radioactive Decay

Alignment

Learning Intentions

By the end of the lesson, students will be able to:

• Distinguish between artificial transmutation and natural radioactive decay.
• Identify evidence in a nuclear equation that shows whether a nuclear change is spontaneous or induced.
• Use conservation of nucleon number and charge number to classify and balance nuclear equations.
• Explain why artificial transmutation usually requires an incoming particle, while natural radioactive decay does not.

Success Criteria

By the end of the lesson, students have successfully:

• Defined natural radioactive decay as a spontaneous nuclear change from an unstable nucleus.
• Defined artificial transmutation as an induced nuclear change caused by bombardment with another particle or nucleus.
• Classified nuclear equations as natural decay or artificial transmutation using equation structure.
• Justified classifications using the terms spontaneous, induced, projectile, target nucleus, daughter nucleus and emitted radiation.
• Balanced simple nuclear equations by conserving mass number and atomic number .

Syllabus Reference

• Unit 1: Thermal, Nuclear and Electrical Physics
• Topic 2: Ionising Radiation and Nuclear Reactions
• Energy and Mass Defect
• Distinguish between artificial transmutations and natural radioactive decay.

Phenomenon

A smoke detector containing americium-241 releases alpha particles without being switched on, heated or struck by another particle. This is natural radioactive decay.

In contrast, some medical radioisotopes are produced when stable or unstable nuclei are deliberately bombarded with neutrons, protons or alpha particles in a reactor or particle accelerator. This is artificial transmutation.

Both processes change one element or isotope into another, but the cause of the change is different.

Key Idea

Natural radioactive decay is spontaneous. Artificial transmutation is induced.

A nucleus undergoing natural radioactive decay changes because it is unstable. No incoming particle is required.

A nucleus undergoing artificial transmutation changes because it is struck by another particle or nucleus. The incoming particle causes the nuclear reaction.

Concept

The concept and thought that best describes the cause of the phenomenon is below.

A nucleus can change its identity when the number of protons in the nucleus changes. Since the atomic number determines the element, any nuclear reaction that changes transmutes one element into another.

Natural radioactive decay:

• begins with one unstable parent nucleus
• occurs spontaneously
• emits radiation such as alpha, beta or gamma radiation
• cannot be predicted for one individual nucleus, but can be predicted statistically using half-life

Artificial transmutation:

• begins with a target nucleus and an incoming projectile
• is induced by collision or bombardment
• often occurs in reactors, particle accelerators or nuclear laboratories
• may produce a new nuclide and one or more emitted particles

Convention

The key conventions associated with the concept and in the branch of established knowledge is below.

Nuclides are written using notation.

• is the mass number, equal to protons plus neutrons.
• is the atomic number, equal to the number of protons.
• is the chemical symbol.

In all nuclear equations:

Common particles include:

Particle	Symbol	Mass number	Atomic number
Alpha particle
Beta minus particle
Beta plus particle
Gamma radiation
Neutron
Proton

Natural radioactive decay often has the structure:

Artificial transmutation often has the structure:

The projectile on the left-hand side is the key sign of artificial transmutation.

Misconceptions

Common misconceptions students have regarding the concept when applying to various situations and solving problems. It could be a conceptual, mathematical or logical misconception.

• Artificial transmutation is not “fake” decay. It is a real nuclear reaction, but it is induced rather than spontaneous.
• Natural radioactive decay does not require a neutron, proton or alpha particle to hit the nucleus first.
• A nuclear equation with two reactants on the left-hand side is usually not natural decay because it involves bombardment or collision.
• Gamma emission alone does not change the element because and do not change.
• If the atomic number changes, the element has changed, even if the chemical symbol is not provided.
• Half-life describes the statistical decay of many nuclei, not the exact time at which one chosen nucleus will decay.

Further Reading

• Natural radioactive decay and nuclear stability
• Artificial transmutation and radioisotope production
• Nuclear equations and conservation of mass number and atomic number
• Medical radioisotopes and radiopharmaceuticals
• Historical work of Rutherford, Curie and Joliot-Curie

Explicit Instruction

Natural radioactive decay and artificial transmutation are both nuclear processes. Both can form a different nuclide, and both must obey conservation of mass number and atomic number.

The distinction is based on the cause of the nuclear change.

Natural radioactive decay occurs because a nucleus is unstable. The nucleus changes spontaneously to become more stable.

Example:

This is natural radioactive decay because there is one parent nucleus on the left-hand side and no incoming projectile.

Artificial transmutation occurs when a nucleus is struck by another particle or nucleus.

Example:

This is artificial transmutation because the nitrogen nucleus is bombarded by an alpha particle.

A useful comparison is:

Feature	Natural radioactive decay	Artificial transmutation
Cause	Instability of the nucleus	Collision with an incoming particle
Trigger	Spontaneous	Induced
Left-hand side of equation	Usually one parent nucleus	Target nucleus plus projectile
Control	Cannot force a specific nucleus to decay at a chosen time	Can be encouraged by supplying projectiles
Example use	Radiometric dating, natural background radiation	Producing medical radioisotopes
Typical equation pattern	Parent daughter radiation	Target projectile product particle(s)

Worked Examples

Worked Example 1

Classify the following reaction as natural radioactive decay or artificial transmutation.

Step 1: Count the reactants on the left-hand side.

There is only one reactant: .

Step 2: Look for an incoming projectile.

There is no projectile on the left-hand side.

Step 3: Identify the emitted radiation.

An alpha particle, , is emitted.

Step 4: Classify the reaction.

This is natural radioactive decay.

Reason: the radium nucleus spontaneously emits an alpha particle and becomes radon.

Check conservation:

Therefore, the equation is balanced.

Worked Example 2

Classify the following reaction as natural radioactive decay or artificial transmutation.

Step 1: Count the reactants on the left-hand side.

There are two reactants: and .

Step 2: Identify the target and projectile.

The target nucleus is .

The projectile is .

Step 3: Classify the reaction.

This is artificial transmutation.

Reason: the nitrogen nucleus is bombarded by an alpha particle, causing it to change into oxygen.

Check conservation:

Therefore, the equation is balanced.

Worked Example 3

Complete and classify the nuclear equation.

Step 1: Balance mass number .

Step 2: Balance atomic number .

Step 3: Identify the missing particle.

A particle with and is a neutron.

Step 4: Write the completed equation.

Step 5: Classify the reaction.

This is artificial transmutation because there is an incoming alpha particle on the left-hand side.

Check for Understanding

Check 1

Classify the reaction below.

Answer:

This is natural radioactive decay.

Reason: carbon-14 is the only reactant. It spontaneously undergoes beta minus decay.

Check 2

Classify the reaction below.

Answer:

This is artificial transmutation.

Reason: beryllium is bombarded by an alpha particle. The incoming alpha particle appears on the left-hand side.

Check 3

A student says:

“Artificial transmutation and natural radioactive decay are the same because both can produce a new element.”

Write a correction.

Answer:

They are similar because both can change the atomic number and produce a new element. However, they are not the same. Natural radioactive decay is spontaneous and occurs because a nucleus is unstable. Artificial transmutation is induced when a target nucleus is struck by an incoming particle.

Investigation (Alternative to Explicit)

Hypothesis

If a nuclear equation includes an incoming projectile on the reactant side, then the reaction is more likely to be artificial transmutation than natural radioactive decay.

Data Collection

Students sort a set of nuclear equations into two groups:

Group A: Natural radioactive decay

Group B: Artificial transmutation

Suggested equations:

For each equation, students record:

• number of reactants on the left-hand side
• whether a projectile is present
• whether radiation or a particle is emitted
• whether and are conserved
• final classification

Analysis

Students identify patterns in the classified equations.

Expected findings:

• Natural radioactive decay usually has one reactant on the left-hand side.
• Artificial transmutation usually has a target nucleus and projectile on the left-hand side.
• Both processes conserve mass number and atomic number.
• Both processes can produce a different element if the atomic number changes.

Evaluation

Students evaluate the classification rule:

“A nuclear equation with one reactant is natural decay; a nuclear equation with two reactants is artificial transmutation.”

This rule is useful for Year 11 examples, but students should recognise that classification should be based on cause, not only equation layout. Natural radioactive decay is spontaneous. Artificial transmutation is induced by bombardment.

Problems

The following problems are designed to help students distinguish artificial transmutation from natural radioactive decay.

1. Classify the reaction and justify your answer.

2. Classify the reaction and justify your answer.

3. Complete the missing particle and classify the reaction.

4. Complete the missing particle and classify the reaction.

5. A student writes:

“Any reaction that releases radiation is natural radioactive decay.”

Explain why this statement is incorrect.

6. A nucleus changes from to by emitting a beta plus particle.

Write the nuclear equation and classify the reaction.

7. A target nucleus of is bombarded with a neutron and forms .

Write the nuclear equation and classify the reaction.

8. Explain why the following reaction changes the element.

9. Compare natural radioactive decay and artificial transmutation using the following terms: spontaneous, induced, projectile, unstable nucleus, target nucleus.

10. Challenge: A nuclear process produces a new isotope but not a new element. Has transmutation occurred? Explain your answer.

Suggested answers:

1. Natural radioactive decay. Polonium emits an alpha particle spontaneously.

2. Artificial transmutation. Boron is struck by a neutron.

3. , natural radioactive decay.

4. Balance : , so . Balance : , so . The missing particle is . This is artificial transmutation.

5. The statement is incorrect because artificial transmutation can also release radiation or particles. The distinction is whether the process is spontaneous or induced.

6. . This is natural radioactive decay.

7. . This is artificial transmutation.

8. Nitrogen has atomic number , while oxygen has atomic number . Since the atomic number changes, the element changes.

9. Natural radioactive decay is spontaneous and occurs when an unstable nucleus changes to become more stable. Artificial transmutation is induced when a target nucleus is struck by a projectile.

10. If the atomic number does not change, the element has not changed. A new isotope may have formed, but transmutation into a different element has not occurred.

Followup

Self-check

Students answer the following questions independently.

1. What word means “happens without being triggered by an incoming particle”?

2. What word means “caused by bombardment or collision”?

3. What feature on the left-hand side of a nuclear equation usually indicates artificial transmutation?

4. Why does changing the atomic number change the element?

5. In one sentence, distinguish between artificial transmutation and natural radioactive decay.

Expected responses:

1. Spontaneous.

2. Induced.

3. A projectile, such as , or .

4. The atomic number equals the number of protons, and the number of protons determines the element.

5. Natural radioactive decay is spontaneous decay of an unstable nucleus, while artificial transmutation is an induced nuclear change caused by bombardment.

Next Topic

Neutron-induced nuclear fission, including the production of extra neutrons and how these neutrons can lead to a fission chain reaction.