Types of Radioactive Decay
Alpha, beta-minus, beta-plus and gamma decay are distinguished by the emitted particles and by how proton number, nucleon number, charge and lepton number are conserved; the specific isotope’s decay mode or half-life is not something to memorize.
Types of Radioactive Decay: quick answer
Alpha, beta-minus, beta-plus and gamma decay are distinguished by the emitted particles and by how proton number, nucleon number, charge and lepton number are conserved; the specific isotope’s decay mode or half-life is not something to memorize. Topic 15.8 is nuclear bookkeeping, not the exponential-decay lesson. First identify what is emitted, then update A and Z and check charge/lepton accounting. Population half-life and decay-constant calculations belong to Topic 15.7.
Do not require memorization of which specific isotope uses which decay mode or its half-life. Neutron emission and electron capture are outside the course framework; detailed neutrino types and weak-force mechanisms are also outside scope.
What you should be able to explain and do
Use these as closed-note retrieval prompts before the worked reasoning.
Distinguish alpha, beta-minus, beta-plus and gamma decay from the emitted products.
Predict how A and Z change for each included decay type.
Balance charge, nucleon number and lepton number in beta-decay equations.
Explain why gamma decay changes nuclear energy but not element/isotope identity.
Terms you need before using the model
Important vocabulary is defined here so the lesson does not depend on an unexplained internal-link jump.
alpha particle
a helium-4 nucleus containing two protons and two neutrons with charge +2e
beta-minus decay
a process in which a neutron changes to a proton while an electron and antineutrino are emitted
beta-plus decay
a process in which a proton changes to a neutron while a positron and neutrino are emitted
gamma decay
de-excitation of a nucleus to a lower energy state by emitting a photon without changing proton or nucleon number
positron
the electron antiparticle with the same mass as an electron and charge +e
neutrino / antineutrino
electrically neutral, negligible-mass particles included in beta-decay conservation bookkeeping
lepton number
a conserved bookkeeping quantity involving electrons/positrons and neutrinos/antineutrinos in the beta-decay processes treated here
Keep variables, conditions and physical meaning together
Select the relationship only after identifying the physical model and representation.
| Relationship | Variables / meaning | Use when | Physical interpretation |
|---|---|---|---|
alpha: A→A−4, Z→Z−2 + ⁴₂He | A parent nucleon number; Z parent proton number; emitted alpha has A=4 and Z=2 | alpha-decay nuclear bookkeeping | the daughter has four fewer nucleons and two fewer protons than the parent |
β−: n→p + e− + anti-ν; β+: p→n + e+ + ν | n neutron; p proton; e− electron; e+ positron; ν neutrino; anti-ν antineutrino | beta-minus or beta-plus decay with charge, nucleon and lepton bookkeeping | β− raises daughter Z by 1 at fixed A; β+ lowers daughter Z by 1 at fixed A |
gamma: excited nucleus → lower-energy same nucleus + γ | γ photon; parent and daughter retain the same A and Z | gamma de-excitation after an excited nuclear state | gamma emission changes nuclear energy but not the element or isotope identity |
Turn evidence into physics
Move physical situation ↔ diagram/graph/equation ↔ verbal claim without losing the model boundary.
Nuclear equation: place A and Z on every nuclear species and balance both sides.
Decay-change table: compare ΔA and ΔZ for α, β−, β+ and γ.
Beta process diagram: show neutron↔proton conversion plus the required charged lepton and neutrino/antineutrino.
Gamma level diagram: show an excited nuclear energy level dropping to a lower state with photon emission.
Change one condition and inspect what responds
Predict first, then move a control. The tool stays inside the topic model.
Two examples with model selection exposed
The point is the reasoning path, not only the final number.
Alpha daughter
Situation: A parent nucleus has A=238 and Z=92 and undergoes alpha decay.
Reasoning: Subtract the emitted alpha particle values: A−4 and Z−2.
Result: The daughter has A=234 and Z=90.
Beta-minus daughter
Situation: A nucleus with A=14 and Z=6 undergoes beta-minus decay.
Reasoning: A neutron becomes a proton; nucleon number stays 14 while Z increases by 1. Electron and antineutrino emission complete the charge/lepton bookkeeping.
Result: The daughter has A=14 and Z=7.
Recognize the physics before reaching for an equation
Use the cue to choose the model, connect it to nearby ideas, then reject any method whose assumptions do not match the situation.
What should trigger Topic 15.8?
Use decay-type bookkeeping when the emitted product determines how nucleon number, proton number, charge, and lepton number change.
How this idea fits the course
This topic classifies individual decay processes, while half-life and exponential population behavior stay in 15.7.
Scope check before solving
Do not require memorization of which specific isotope uses which decay mode or its half-life. Neutron emission and electron capture are outside the course framework; detailed neutrino types and weak-force mechanisms are also outside scope.
How would the evidence test the model?
Identify what changes, what is measured, the graph/representation that tests the relationship, and the uncertainty that matters.
Errors to remove before more practice
Repair the model or representation decision before doing extra arithmetic.
Putting half-life calculations in Topic 15.8
Half-life and exponential population decay are Topic 15.7; 15.8 focuses on decay mechanisms and conservation bookkeeping.
Changing A during beta decay
A neutron and proton are both nucleons, so beta-minus or beta-plus changes Z but not A.
Changing Z during gamma decay
Gamma emission changes nuclear energy state but leaves A and Z unchanged.
Adding electron capture or neutron emission
Those processes are outside the required course framework.
Six checks before moving on
Close the notes and test transfer before switching to the separate practice pages.
- I can define every important term used in this lesson.
- I can choose the model before selecting an equation.
- I can translate between the key representation and a verbal prediction.
- I can state the relationship conditions and scope boundary.
- I can design or interpret evidence that tests the model.
- I can explain the topic without relying on question-pattern memorization.
Practice is kept on its dedicated pages
Finish the lesson first. Then open the separate topic bank when you want exam-style practice without replacing the teaching content above.
42 multiple-choice questions
Use the exact-topic MCQ bank to test model selection, representations, calculations and boundaries after learning the concept.
Open 42 Topic MCQs4 multipart free-response tasks
Use the exact-topic FRQ set for mathematical, representation, experimental and qualitative/quantitative reasoning.
Open 4 Topic FRQsTopic 15.8 FAQs
What decay types are included?
Alpha, beta-minus, beta-plus and gamma decay.
What happens to A and Z in alpha decay?
A decreases by 4 and Z decreases by 2.
What happens in beta-minus decay?
A neutron changes to a proton while an electron and antineutrino are emitted; A stays the same and Z increases by 1.
What happens in beta-plus decay?
A proton changes to a neutron while a positron and neutrino are emitted; A stays the same and Z decreases by 1.
Does gamma decay change the element?
No. A and Z remain unchanged; only the nuclear energy state decreases.
Do I need isotope-specific decay modes or half-lives memorized?
No. Use supplied information and apply the conservation/bookkeeping rules.