Physics · JEE Advanced only

Alpha, Beta and Gamma Radiations (JEE Advanced)

Not in the JEE Main syllabus, but it is in JEE Advanced. Study time: about 3 to 4 hours for concepts, decay equations, and practice problems. Add 1 hour if you need to revise mass-energy equivalence basics..

Last updated: 26 October 2026

Direct answer

Alpha, beta and gamma radiations are the three types of emissions from unstable atomic nuclei.

Alpha, beta and gamma radiations are the three types of emissions from unstable atomic nuclei. Alpha particles are helium nuclei (2 protons + 2 neutrons), beta particles are high-speed electrons or positrons, and gamma rays are high-energy electromagnetic waves. Understanding their properties, penetrating power, and the nuclear transformations they cause is essential for JEE Advanced.

Official syllabus

What the JEE Advanced syllabus says

“α, β and γ radiations”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: nuclear fission and fusion.

JEE Main covers nuclear fission and fusion but skips the detailed physics of radioactive emissions. For Advanced, you need to know how each radiation type changes the parent nucleus and solve problems involving decay equations and energy calculations.

Key ideas

What you must understand

Alpha (α) particles: ₂He⁴ nuclei, +2 charge, least penetrating, stopped by paper, highest ionizing power
Beta (β⁻) particles: electrons emitted when a neutron converts to proton; β⁺ (positron) when proton converts to neutron
Gamma (γ) rays: pure energy (photons), no mass or charge, most penetrating, accompanies alpha/beta decay to release excess energy
In α-decay: mass number decreases by 4, atomic number decreases by 2
In β⁻ decay: mass number unchanged, atomic number increases by 1; in β⁺ decay: atomic number decreases by 1
Gamma emission does not change mass number or atomic number, only releases energy from excited nucleus

Formulas

Formulas and key facts

α-decay: ᴢXᴬ → ᴢ₋₂Yᴬ⁻⁴ + ₂He⁴
β⁻ decay: ᴢXᴬ → ᴢ₊₁Yᴬ + e⁻ + ν̄ (antineutrino)
β⁺ decay: ᴢXᴬ → ᴢ₋₁Yᴬ + e⁺ + ν (neutrino)
Q-value (energy released) = (mass of reactants − mass of products) × c²
Kinetic energy of α-particle: Kα = Q × (A−4)/A (approximately, for recoil consideration)
Penetrating power: γ > β > α
Ionizing power: α > β > γ
1 amu = 931.5 MeV/c²

Avoid

Common mistakes

Forgetting that in β-decay, a neutrino or antineutrino is also emitted, which carries away some energy
Confusing β⁻ and β⁺ decay: β⁻ increases atomic number, β⁺ decreases it
Assuming gamma rays change the nucleus composition; they only release energy, not particles
Ignoring recoil of the daughter nucleus when calculating kinetic energy of emitted alpha particle

Worked example

A JEE Advanced-level example

Question. A nucleus ²²⁶₈₈Ra undergoes α-decay. The atomic masses are: Ra-226 = 226.0254 u, Rn-222 = 222.0176 u, He-4 = 4.0026 u. Calculate the Q-value of the decay and the kinetic energy of the emitted α-particle (assuming the parent nucleus is at rest).

Show solution

Write the decay equation: ²²⁶₈₈Ra → ²²²₈₆Rn + ⁴₂He
Calculate mass defect: Δm = 226.0254 − (222.0176 + 4.0026) = 226.0254 − 226.0202 = 0.0052 u
Convert to energy (Q-value): Q = 0.0052 × 931.5 MeV = 4.84 MeV
For α-particle kinetic energy, use momentum conservation. Since parent is at rest: Kα = Q × (A−4)/A = 4.84 × (222/226)
Calculate: Kα = 4.84 × 0.9823 = 4.75 MeV

Answer: Q-value = 4.84 MeV; Kinetic energy of α-particle ≈ 4.75 MeV

Solved twice independently; both solutions agree.

FAQs

Frequently asked questions

Is Alpha, Beta and Gamma Radiations in the JEE Main syllabus?

No. It is in the JEE Advanced 2026 syllabus only. The closest JEE Main topic is nuclear fission and fusion.

How long does Alpha, Beta and Gamma Radiations take to prepare for JEE Advanced?

About 3 to 4 hours for concepts, decay equations, and practice problems. Add 1 hour if you need to revise mass-energy equivalence basics., if you already know the related JEE Main topic.