Difference Between Alpha, Beta, and Gamma Decay (Table & Examples)
Radioactive decay is a spontaneous process where unstable nuclei release energy to become more stable. Three main types—alpha decay, beta decay, and gamma decay—show up in JEE Main, board exams, and competitive entrance questions. Understanding their differences, equations, and practical uses is essential for mastering nuclear physics and scoring well.
Alpha, beta, and gamma decay processes each involve distinct changes to an atom's nucleus. These concepts also link closely to nuclear binding energy, electromagnetic radiation, and the structure of atomic nuclei. This topic also appears in practice worksheets and numerical questions, so careful study is advised.
Alpha Beta and Gamma Decay: Definition and Mechanism
Alpha beta and gamma decay are the three principal forms of radioactive decay. Each involves emission of a specific particle or electromagnetic radiation, resulting in different nuclear transformations. Their unique equations and examples are important semantic variants of the main topic and must be remembered.
Alpha decay occurs primarily in heavy nuclei (mass number ≥210), where the nucleus releases two protons and two neutrons as an alpha particle (He2+). This transforms the original element into a daughter nucleus with atomic number reduced by two and mass number reduced by four.
- Example: Uranium-238 alpha decay yields Thorium-234 plus an alpha particle.
- Alpha particle formula: 4He or 4₂He
- Equation: AZX → A-4Z-2Y + 42He
Beta decay is observed in nuclei with neutron-proton imbalance. In beta minus decay (β-), a neutron transforms into a proton, emitting an electron and antineutrino. In beta plus decay (β+), a proton becomes a neutron, emitting a positron and neutrino. The atomic number increases by one for β-, decreases by one for β+; mass number remains unchanged.
- Beta minus decay: 3215P → 3216S + e- + ̅ν
- Beta plus decay: 2211Na → 2210Ne + e+ + ν
- Beta rays are high-energy electrons (β-) or positrons (β+).
Gamma decay happens when a nucleus in an excited energy state emits a gamma (γ) photon and drops to a lower energy level. There is no change in proton or neutron count; only energy is released. Gamma emission usually follows alpha or beta decay to stabilize the nucleus's energy.
- Gamma rays are electromagnetic waves with high frequency and zero charge.
- No change in atomic or mass number.
- Example: 6027Co → 6028Ni + γ
Comparing Alpha Beta and Gamma Decay: Table of Differences
| Parameter | Alpha Decay | Beta Decay | Gamma Decay |
|---|---|---|---|
| Emitted Particle | Helium nucleus (α) | Electron (β-) or positron (β+) | Photon (γ ray) |
| Change in Atomic Number | -2 | ±1 | 0 |
| Change in Mass Number | -4 | 0 | 0 |
| Penetrating Power | Lowest | Medium | Highest |
| Ionizing Power | Very high | Intermediate | Low |
| Typical Equation | AZX → A-4Z-2Y + α | AZX → AZ±1Y + β + ν | AZX* → AZX + γ |
Alpha Beta and Gamma Decay: Key Equations and Worked Example
Remembering the main equations of alpha beta and gamma decay simplifies nuclear reaction calculations. Always balance both atomic and mass numbers on either side. Pay attention to symbols: Z (proton number), A (mass number), X (parent element), Y (daughter element).
- Alpha decay: AZX → A-4Z-2Y + α
- Beta minus decay: AZX → AZ+1Y + β- + ̅ν
- Beta plus decay: AZX → AZ-1Y + β+ + ν
- Gamma decay: AZX* → AZX + γ
Sample problem: If 21084Po undergoes alpha decay, write the product nucleus.
- Subtract 2 from Z: 84 – 2 = 82
- Subtract 4 from A: 210 – 4 = 206
- So, product is 20682Pb + α
These different equations allow quick reference while solving MCQs or practice worksheets on nuclear decay. For more advanced questions or mock tests, see modern physics and atoms and nuclei practice papers.
Alpha Beta and Gamma Decay: Practical Applications and Study Tips
The concepts of alpha beta and gamma decay are widely used in medicine, science, and industry. Understanding their distinctions prevents confusion, especially in numericals or conceptual questions. For regular revision, refer to atom and nuclei and physics and measurement revision notes.
- Alpha particles: Smoke detectors, cancer therapy, Rutherford scattering experiments.
- Beta particles: Tracer studies in medicine, thickness monitoring in industry, PET scans.
- Gamma rays: Sterilization, imaging (MRI, CT), disinfection, structural tests in engineering.
- Practice: Use atoms and nuclei mock tests and topic-based questions regularly.
- Correct symbols are key. Don’t confuse positrons (β+) and electrons (β-).
Common mistakes include neglecting emitted neutrinos, sign errors in beta decay, or failing to conserve charge and mass numbers. These can cost marks in JEE Main or board exams. Worksheets and solved questions from Vedantu clarify doubted steps and provide valuable exam practice.
Alpha beta and gamma decay topics also connect with law of radioactive decay, binding energy, and related chapters. Linking your understanding across these subtopics will benefit your overall grasp of nuclear physics.
- For concepts like cause of radioactivity and nuclear fission and nuclear reactor, review related Vedantu notes.
- Check out comparisons with properties of alpha beta and gamma rays.
- For further practice, solve important questions on atom and nuclei and revision notes.
Mastery of alpha beta and gamma decay helps in solving nuclear equation questions, distinguishing radiation types, and interpreting real-life decay chains. For continuous practice, try mock test series tailored to JEE Main and boards.
In summary, alpha beta and gamma decay remain essential foundation topics for exams and later scientific study. Clear grasp of equations, processes, and differences ensures confidence during competitive tests. Rely on Vedantu’s expertly designed material for targeted practice and deeper understanding of nuclear physics concepts.
FAQs on Alpha, Beta, and Gamma Decay Explained for JEE & NEET
1. What is alpha, beta, and gamma decay?
Alpha, beta, and gamma decay are three main types of radioactive decay processes seen in unstable atomic nuclei.
- Alpha decay: The nucleus emits an alpha particle (2 protons and 2 neutrons).
- Beta decay: The nucleus changes a neutron into a proton, emitting a beta particle (electron or positron).
- Gamma decay: The nucleus releases excess energy as a gamma ray (electromagnetic radiation) without emitting a particle.
2. What is the main difference between alpha, beta, and gamma decay?
The main difference lies in the type of radiation emitted and how the nucleus changes:
- Alpha decay: Emits a helium nucleus; decreases atomic number by 2 and mass by 4.
- Beta decay: Emits an electron or positron; changes atomic number by ±1, mass remains unchanged.
- Gamma decay: Emits electromagnetic energy; does not change atomic number or mass.
3. How does alpha decay change the atomic nucleus?
During alpha decay, an unstable nucleus emits an alpha particle (2 protons and 2 neutrons).
- The atomic number decreases by 2.
- The mass number decreases by 4.
- The resulting element shifts two places lower in the Periodic Table.
4. What changes occur in the nucleus during beta decay?
In beta decay, the nucleus either emits an electron (beta minus) or a positron (beta plus).
- Beta minus (β⁻) decay: A neutron turns into a proton, emitting an electron. Atomic number increases by 1.
- Beta plus (β⁺) decay: A proton turns into a neutron, emitting a positron. Atomic number decreases by 1.
- Mass number remains the same in both cases.
5. What is the effect of gamma decay on atomic number and mass number?
Gamma decay only releases energy as gamma rays without changing the atomic or mass number.
- Atomic number: No change
- Mass number: No change
- The nucleus simply moves from a higher to a lower energy state.
6. Can a nucleus undergo more than one type of decay?
Yes, some unstable nuclei can experience a series of decays, often emitting different types of radiation:
- For example, a nucleus may first undergo alpha decay, then the new nucleus may undergo beta decay.
- Often, gamma rays are emitted after either alpha or beta decay to release excess energy.
7. What are some real-life applications of alpha, beta, and gamma rays?
Alpha, beta, and gamma rays are important in various fields:
- Alpha particles: Used in smoke detectors, cancer treatment (targeted therapy).
- Beta particles: Helpful in medical diagnostics (radioactive tracers), industrial thickness gauges.
- Gamma rays: Used in sterilizing medical equipment, cancer radiotherapy, and imaging techniques.
8. Do all radioactive elements emit all three types of rays?
No, not every radioactive element emits all three forms of radiation.
- Which emission occurs depends on the isotope's nuclear structure and stability.
- Many undergo only one type of decay, but some can emit both beta and gamma, or alpha and gamma.
9. Why is gamma decay often seen after alpha or beta decay?
Gamma decay is often observed after alpha or beta decay because the nucleus may be left in an excited state.
- After emitting an alpha or beta particle, the nucleus releases excess energy as gamma rays to become more stable.
- This step does not alter the atomic or mass numbers.
10. How do the equations for alpha and beta decay differ?
Equations for alpha decay and beta decay differ by the particles released and resulting changes:
- Alpha decay: A → B + α (mass number decreases by 4, atomic number by 2).
- Beta minus decay: A → B + β⁻ + ν̅ (atomic number increases by 1, mass unchanged).
- Beta plus decay: A → B + β⁺ + ν (atomic number decreases by 1, mass unchanged).
