Radioactive Decay Series
Nuclei
7
JEE Qs
8%
Hard
75
min
Master the balancing of mass and atomic numbers for each decay type and practice calculating the total alpha and beta particles in a complete series transformation.
🧮 Key Formulas
✅ Key Points for JEE
- 1Radioactive decay series are sequences of successive decays that transform an unstable parent nucleus into a stable daughter nucleus.
- 2There are four major radioactive decay series based on the mass number (A): 4n (Thorium series), 4n+1 (Neptunium series, extinct), 4n+2 (Uranium series), and 4n+3 (Actinium series). Each series maintains its 'n' form throughout.
- 3Alpha decay decreases mass number (A) by 4 and atomic number (Z) by 2. Beta-minus decay leaves A unchanged but increases Z by 1. Beta-plus decay leaves A unchanged but decreases Z by 1. Gamma decay changes neither A nor Z.
- 4For a complete decay series, the total number of alpha and beta particles emitted can be calculated by comparing the initial and final mass and atomic numbers.
- 5The stable end product for most natural decay series is an isotope of Lead (Pb).
⚠️ Common Mistakes
- ✕Incorrectly balancing mass number (A) and atomic number (Z) during alpha and beta decays, leading to errors in determining daughter nuclei.
- ✕Confusing the effect of beta-minus (electron emission) and beta-plus (positron emission) on the atomic number Z.
- ✕Errors in calculating the total number of alpha and beta decays required to reach a stable end product from a given parent nucleus, especially sign errors in the formulas.
- ✕Misidentifying the type of decay series (4n, 4n+1, etc.) or forgetting common parent/daughter isotopes.
📝 Practice Questions
See allQ32.Choose the correct nuclear process from the below options [p: proton, n : neutron, e− : electron, e+ : positron, v : neutrino, ¯v : antineutrino] (1) n →p + e+ + ¯v (2) n →p + e+ + v (3) n →p + e−+ v (4) n →p + e−+ ¯v
Q40.A radioactive nucleus n2 has 3 times the decay constant as compared to the decay constant of another radioactive nucleus n1 . If initial number of both nuclei are the same, what is the ratio of number of nuclei of n2 to the number of nuclei of n1 , after one half-life of n1 ? (1) 1/8 (2) 8 (3) 4 (4) 1/4
Q18.Binding energy of a certain nucleus is 18 × 108 J. How much is the difference between total mass of all the nucleons and nuclear mass of the given nucleus: (1) 10μg (2) 20μg (3) 0.2μg (4) 2μg
Q19.Which of the following nuclear fragments corresponding to nuclear fission between neutron (10n) and uranium isotope (23592 U) is correct : (1) 144 56 Ba + 8936Kr + 410n (2) 14456 Ba + 8936Kr + 310n (3) 140 56 Xe + 9438Sr + 310n (4) 15351 Sb + 9941Nb + 310n
Q30.If three helium nuclei combine to form a carbon nucleus then the energy released in this reaction is _____ ×10−2MeV . (Given 1u = 931MeV/c2 , atomic mass of helium = 4.002603u )
Q30.The radius of a nucleus of mass number 64 is 4 . 8 fermi. Then the mass number of another nucleus having radius of 4 fermi is 1000 where 𝑥 is _________. 𝑥,
NCERT Chapters
- Class 12 Physics Ch 13: Nuclei