JEE Physics Focus Reading Time: 10 min 3 Decay Types

How to Never Get Confused Between Alpha, Beta, and Gamma Decay Again

Clear comparison of displacement laws, mass changes, energy spectra, and memory tricks for JEE Physics.

Decay Types

100%

JEE Relevance

Memory Tricks

12min

Study Time

Why Understanding Decay Types is Crucial for JEE

Nuclear decay questions appear in every JEE Main paper and frequently in JEE Advanced. Mastering these 3 decay types helps you:

Quickly solve displacement law problems
Predict daughter nuclei accurately
Understand energy spectra for advanced questions
Score easy marks in nuclear physics section

Alpha Decay Heavy Nuclei

α-Decay: Helium Nucleus Emission

Displacement Law:

$$^A_ZX \rightarrow ^{A-4}_{Z-2}Y + ^4_2\alpha$$

🔍 Key Characteristics:

Mass Number: Decreases by 4
Atomic Number: Decreases by 2
Particle: Helium nucleus (2p + 2n)
Penetration: Low (stopped by paper)

📊 Energy Spectrum:

Discrete energies
Sharp line spectrum
High energy (4-9 MeV)
Monochromatic

💡 Memory Trick:

"Alpha = All numbers go down (A-4, Z-2)"

Beta Decay Neutron Rich

β-Decay: Electron Emission

Displacement Law:

$$^A_ZX \rightarrow ^A_{Z+1}Y + ^0_{-1}\beta + \bar{\nu}$$

🔍 Key Characteristics:

Mass Number: Unchanged
Atomic Number: Increases by 1
Particle: Electron from nucleus
Penetration: Medium (stopped by Al)

📊 Energy Spectrum:

Continuous spectrum
Range from 0 to E_max
Energy shared with neutrino
Average energy ≈ E_max/3

💡 Memory Trick:

"Beta = Balance changes (n→p), mass same"

Gamma Decay Energy Release

γ-Decay: Electromagnetic Radiation

Displacement Law:

$$^A_ZX^* \rightarrow ^A_ZX + \gamma$$

🔍 Key Characteristics:

Mass Number: Unchanged
Atomic Number: Unchanged
Particle: High-energy photon
Penetration: High (needs Pb)

📊 Energy Spectrum:

Discrete energies
Sharp line spectrum
Nuclear energy levels
Monochromatic

💡 Memory Trick:

"Gamma = Goes through everything, changes nothing"

📊 Quick Comparison Table

Property	Alpha	Beta	Gamma
Mass Change	A-4	No change	No change
Atomic Number	Z-2	Z+1	No change
Nature	Helium nucleus	Electron/Positron	EM radiation
Penetration	Low	Medium	High
Energy Spectrum	Discrete	Continuous	Discrete

🚀 Exam Solving Strategies

Problem Approach:

First identify decay type from mass/atomic number changes
Apply displacement law systematically
Check energy conservation in calculations
Remember neutrino in beta decay energy distribution

Common Pitfalls:

Forgetting antineutrino in beta decay
Confusing beta-minus and beta-plus decay
Missing excited state in gamma decay
Wrong penetration power order

Advanced Concepts Available

Includes beta-plus decay, electron capture, decay chains, and JEE Advanced level problems

📝 Quick Self-Test

Try these JEE-level problems to test your understanding:

1. ²³⁸₉₂U undergoes alpha decay. Find the daughter nucleus.

2. ¹⁴₆C undergoes beta decay. Write the complete equation.

3. Why does beta decay have continuous spectrum while alpha has discrete?

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