How Does Alpha Decay Change the Nucleus? (Step-by-Step Guide)
Alpha decay is a type of radioactive disintegration in which certain unstable atomic nuclei release excess energy by ejecting an alpha particle. In this process, the nucleus becomes more stable by emitting a particle that consists of two protons and two neutrons, which is identical to a helium nucleus.
This phenomenon is mostly observed among elements whose nuclei are heavier than bismuth and also among some of the rare-earth elements, specifically from neodymium to lutetium. These heavy elements experience instability due to their large and complex nuclei, making alpha decay a common mode of radioactive transformation for them.
Definition and Characteristics of Alpha Decay
During alpha decay, the original unstable nucleus emits an alpha particle. As a result, the atomic number of the element decreases by 2 and the mass number decreases by 4. This means the atom transforms into a new element that is placed two positions prior in the periodic table.
Alpha decay helps certain heavy nuclei release some of their nuclear mass and energy, leading to a more stable nuclear configuration.
The materials that typically undergo alpha decay are usually found in the group of actinides and among elements with very large atomic numbers.
General Representation and Formula
The alpha decay process can be represented by a general nuclear reaction where a parent nucleus loses 2 protons and 2 neutrons.
The transformation can be written as:
AZX → A-4Z-2Y + 42He
Where:
- X = Parent (original) nucleus
- Y = Daughter nucleus (new element)
- A = Mass number of parent
- Z = Atomic number of parent
- 42He = Alpha particle
Example of Alpha Decay
Consider an element heavier than bismuth, which undergoes alpha decay. For instance, a nucleus of one heavy element ejects an alpha particle, resulting in a lighter and more stable nucleus.
The rare-earth elements from neodymium to lutetium also show this process but the principal examples are the heavy elements occurring after bismuth in the periodic table.
Step-by-Step Approach to Alpha Decay Problems
1. Identify the parent nucleus and write its atomic and mass numbers.
2. Subtract 2 from the atomic number (Z) and 4 from the mass number (A) to find the daughter nucleus.
3. Write the nuclear equation showing the release of an alpha particle (42He).
Key Features of Alpha Emitters
- The principal alpha emitters are elements heavier than bismuth.
- Rare-earth elements between neodymium and lutetium may also undergo alpha emission.
- Alpha decay always produces a new element (the daughter) that is lighter and sits two places earlier on the periodic table.
| Property | Description |
|---|---|
| Emitted Particle | Alpha particle (Helium nucleus, two protons and two neutrons) |
| Effect on Atomic Number | Decreases by 2 |
| Effect on Mass Number | Decreases by 4 |
| Occurs in | Elements heavier than bismuth; some rare-earth elements |
| Typical Result | Formation of a new, lighter element |
Practical Example of Alpha Decay Calculation
Suppose a heavy nucleus such as Element X with atomic number Z and mass number A emits an alpha particle. The resulting equation is:
AZX → A-4Z-2Y + 42He
For a specific example and deeper practice, refer to:
Alpha Decay - In-depth Guide
Key Formulas and Applications
| Formula Type | Application | Result |
|---|---|---|
| General Alpha Decay | Any element heavier than bismuth | AZX → A-4Z-2Y + 42He |
Related Concepts for Deeper Exploration
- Radioactivity - Alpha Decay
- Radioactivity - Beta Decay
- Radioactivity - Gamma Decay
- Nuclear Binding Energy
- Atomic Physics Concepts
Summary and Next Steps
Alpha decay is a fundamental nuclear process that lowers the mass and atomic number of heavy, unstable nuclei. It is mostly observed in elements heavier than bismuth and in some rare-earth elements.
Understanding this process helps in grasping the broader topic of radioactivity. Continue exploring related topics and solving practice problems at Vedantu to master nuclear physics.
FAQs on Alpha Decay in Radioactivity: Equations, Process & Examples
1. What is alpha decay?
Alpha decay is a type of radioactive decay in which an unstable atomic nucleus releases excess energy by emitting an alpha particle. An alpha particle consists of 2 protons and 2 neutrons, which is the same as a helium nucleus. This process reduces the mass number of the parent nucleus by 4 and the atomic number by 2, resulting in a new element called the daughter nucleus.
2. What is the general equation for alpha decay?
The general equation for alpha decay is as follows:
AZX → A-4Z-2Y + 42He
Here,
• AZX: Parent nucleus
• A-4Z-2Y: Daughter nucleus
• 42He: Alpha particle (helium nucleus)
3. Why does alpha decay occur?
Alpha decay usually occurs in heavy, unstable nuclei that have too many protons, making them energetically unstable. By emitting an alpha particle, the nucleus moves toward a more stable energy state because:
• Ejection of an alpha particle lowers both mass number and atomic number
• It helps release nuclear binding energy
• This process increases the stability of the atom
4. What is emitted during alpha decay?
During alpha decay, the nucleus emits an alpha particle. An alpha particle contains 2 protons and 2 neutrons, which is the same as the nucleus of a helium-4 atom (42He).
5. How does alpha decay affect mass number (A) and atomic number (Z) of the nucleus?
Alpha decay decreases the mass number (A) of the nucleus by 4 and the atomic number (Z) by 2. This means:
• The atom changes into a different element (daughter nucleus)
• Both numbers are reduced as a result of losing an alpha particle
6. Give an example of an alpha decay reaction.
Example: Uranium-238 (23892U) undergoes alpha decay as follows:
23892U → 23490Th + 42He
Here,
• The parent nucleus is uranium-238
• The daughter nucleus is thorium-234
• The emitted alpha particle is a helium nucleus
7. How do you calculate the energy released (Q-value) in an alpha decay reaction?
To calculate energy released (Q-value) in an alpha decay:
• Q = [Mass of Parent – (Mass of Daughter + Mass of Alpha Particle)] × 931.5 MeV
• 1 atomic mass unit (u) equals 931.5 MeV
8. What are the differences between alpha, beta, and gamma decay?
Differences between alpha, beta, and gamma decay:
• Alpha decay: Emits a helium nucleus, reduces mass number by 4, atomic number by 2
• Beta decay: Emits an electron or positron, changes atomic number by ±1, mass number unchanged
• Gamma decay: Emits a photon, no change in mass or atomic number
• Penetration power: Alpha (low), Beta (medium), Gamma (high)
• Danger: Alpha is hazardous if ingested, Gamma is hazardous in external exposure
9. Is alpha radiation dangerous to humans?
Alpha radiation is dangerous if alpha-emitting materials are inhaled, ingested, or enter open wounds because:
• They cause severe damage to living tissues at close range
• Alpha particles cannot penetrate skin but are very harmful internally
• Proper handling and containment are necessary for safety
10. Where is alpha decay commonly observed?
Alpha decay is commonly found in naturally occurring radioactive elements, especially those heavier than lead (Z > 82), such as uranium, thorium, and radium. These elements undergo alpha decay as part of their natural radioactive decay series.
11. What is an alpha particle?
An alpha particle is a positively charged particle made up of 2 protons and 2 neutrons—the same as a helium-4 nucleus. Its symbol is 42He or α. It is emitted during alpha decay.
12. Can alpha decay be used for any practical applications?
Yes, alpha decay has practical uses in:
• Smoke detectors (using Americium-241)
• Medical treatments (targeted alpha therapy for cancer)
• Power sources (radioisotope thermoelectric generators for space missions)
These applications make use of the properties of alpha-emitting isotopes under controlled conditions.
