How Does Beta Decay Change Atomic Number and Isotopes?
Beta decay is a form of radioactive disintegration in which unstable atomic nuclei spontaneously emit particles, leading to a change of one unit in positive charge without any alteration in the mass number of the nucleus. This process allows the nucleus to dissipate excess energy and become more stable. There are three recognized processes within beta decay: electron emission, positron emission, and electron capture. Each process results in a different transformation within the nucleus but shares the key property that the overall mass number remains unchanged.
Detailed Explanation of Beta Decay
In beta decay, the nucleus undergoes a transformation that changes its charge by one unit. This process can occur in several ways:
- Electron emission: An unstable nucleus emits an electron (often called a beta-minus, or β⁻ particle). This turns a neutron into a proton, increasing the atomic number by one.
- Positron emission: A proton in the nucleus transforms into a neutron as a positron (β⁺ particle) is emitted, reducing the atomic number by one.
- Electron capture: The nucleus captures one of its own atomic electrons, which interacts with a proton to form a neutron. This also decreases the atomic number by one.
Despite these changes in charge, the total number of nucleons (protons + neutrons, i.e., the mass number) remains the same throughout the decay process.
Formulas and Key Equations
| Beta Decay Type | Nuclear Equation | Atomic Number Change | Mass Number Change |
|---|---|---|---|
| Electron Emission (β⁻) | n → p + e- | +1 | 0 |
| Positron Emission (β⁺) | p → n + e+ | -1 | 0 |
| Electron Capture | p + e- → n | -1 | 0 |
Example of Beta Decay
Consider a nucleus that undergoes electron emission (β⁻ decay). In this scenario, a neutron is converted into a proton while emitting an electron. For example:
Similarly, for positron emission, a proton is converted into a neutron with the emission of a positron:
In electron capture, an internal electron combines with a proton, forming a neutron and reducing the atomic number by one.
Step-by-Step Approach to Beta Decay Problems
| Step | Process | Example |
|---|---|---|
| 1 | Identify the nucleus and type of beta decay | Isotope: 14C, Decay: β⁻ (electron emission) |
| 2 | Note the change in atomic number (±1) | Z (atomic number) increases from 6 to 7 |
| 3 | Write the product nucleus | 14N is formed |
| 4 | Balance the reaction with emitted particle | + e- |
This approach applies to all three types of beta decay, allowing you to track changes in atomic number without affecting the mass number.
Comparison with Other Radioactive Decay Types
| Decay Type | Particle Emitted | Change in Atomic Number | Change in Mass Number |
|---|---|---|---|
| Alpha Decay | Helium nucleus (2 protons and 2 neutrons) | -2 | -4 |
| Beta Decay | Electron or positron | ±1 | 0 |
This table highlights that, unlike alpha decay, beta decay does not affect the mass number but only changes the nuclear charge by one unit.
Applications and Next Steps
A strong grasp of beta decay is essential for nuclear physics and for understanding various applications of radioactivity in science, medicine, and industry. Further study can help you analyze decay reactions, identify resulting isotopes, and understand how the process stabilizes the nucleus.
For deeper insight and practice, explore:
- Radioactivity Beta Decay for structured learning.
- Beta Decay: In-Depth Notes to understand mechanisms further.
- Alpha Decay Explained to compare nuclear processes.
- Overview of Gamma Decay for more on nuclear transitions.
- Atomic Physics and Nucleus Structure for foundational concepts.
Practice Problem
A certain isotope undergoes positron emission (β⁺ decay). What is the effect on its atomic and mass numbers?
- The atomic number decreases by one.
- The mass number remains unchanged.
Use the stepwise approach shown above to solve more practice problems and build mastery.
Summary
- Beta decay involves the emission of electrons or positrons, changing the nuclear charge by one while keeping mass number the same.
- Three processes are recognized: electron emission, positron emission, and electron capture.
- Mastering the step-by-step analysis ensures accurate predictions for nuclear reactions and exam questions.
- Continue practice and explore Vedantu Physics resources to deepen understanding and prepare for advanced problems.
FAQs on Understanding Beta Decay in Radioactivity: Definition, Types & Equations
1. What is beta decay in radioactivity?
Beta decay is a type of radioactive decay in which an unstable atomic nucleus transforms by converting a neutron into a proton (beta minus decay) or a proton into a neutron (beta plus decay). This process emits a beta particle (electron or positron) and a neutrino or antineutrino, changing the atomic number of the element by one but leaving the mass number unchanged.
2. What changes occur in atomic and mass numbers after beta decay?
Beta decay affects atomic number and mass number as follows:
Beta minus decay (β-):
• Atomic number increases by 1.
• Mass number remains the same.
Beta plus decay (β+):
• Atomic number decreases by 1.
• Mass number remains the same.
These changes occur due to the conversion of a neutron to a proton or vice versa in the nucleus.
3. What is the typical equation for beta minus decay?
The standard beta minus decay equation:
n → p + e- + ν̄e
Here:
• n: Neutron
• p: Proton
• e-: Beta particle (electron)
• ν̄e: Antineutrino
This shows a neutron in the nucleus transforms into a proton, emitting an electron and antineutrino.
4. How does beta decay differ from alpha and gamma decay?
Key differences:
• Alpha decay: Emission of a helium nucleus (2 protons, 2 neutrons); mass number decreases by 4 and atomic number by 2.
• Beta decay: Emission of an electron or positron; atomic number changes by ±1, mass number unchanged.
• Gamma decay: Emission of high-energy photon; no change in mass or atomic number, only excess energy is released.
Beta decay uniquely changes the atomic number by 1 without altering the mass number.
5. What are the types of beta decay?
Beta decay occurs in two main types:
• Beta minus (β-) decay: A neutron changes into a proton, releasing an electron and an antineutrino.
• Beta plus (β+) decay: A proton changes into a neutron, emitting a positron and a neutrino.
Each type results in a change in the atomic number of the nucleus by one unit.
6. Is the mass number affected in beta decay?
No, beta decay does not change the mass number. Only the atomic number changes by ±1. The nucleon (total protons and neutrons) count remains the same, as a neutron is converted to a proton or vice versa, but the sum stays constant.
7. What happens to the identity of an element after beta minus decay?
After beta minus decay, the atom’s atomic number increases by 1, so it transforms into a new element (next element in the periodic table), while the mass number remains unchanged. For example, 14C becomes 14N after beta minus decay.
8. Why are neutrinos or antineutrinos emitted during beta decay?
Neutrinos (or antineutrinos) are emitted in beta decay to conserve energy, momentum, and angular momentum. Their presence ensures that:
• The sum of energy and momentum before and after the decay remains balanced.
• These particles are nearly massless, neutral, and interact very weakly with matter.
9. Give an example of a nuclear equation for beta plus decay.
An example of beta plus decay:
22Na11 → 22Ne10 + e+ + νe
Here, sodium-22 decays to neon-22, emitting a positron and a neutrino. The atomic number decreases by 1, mass number unchanged.
10. How can you quickly identify the product element in a beta minus decay problem?
To identify the product of beta minus decay:
1. Note parent’s atomic number (Z) and mass number (A).
2. For beta minus: increase the atomic number by 1 (Z + 1), mass number (A) remains unchanged.
3. Find the element with new atomic number (Z + 1) in the periodic table.
This gives the daughter nucleus or the new element formed.
11. What are practical applications of beta decay?
Beta decay applications include:
• Medical imaging and treatment (PET scans)
• Dating of archaeological and geological samples (carbon-14 dating)
• Industrial thickness measurement
Beta particles’ predictable energy and penetration are useful in these fields.
12. Why is beta decay important for Physics exams like JEE and NEET?
Beta decay is a key concept in Modern Physics sections of exams like JEE and NEET because:
• It tests understanding of atomic structure and nuclear reactions.
• Numerical problems based on beta decay equations are common.
• It aligns directly with NCERT syllabus and commonly appears in exam questions, making it essential for scoring well.
