Verified Solution • 2025–26 Session moderate

QPages 442-444: Q29: HC Verma: Concepts of Physics - Volume 2 The Nucleus Pages 442-444: Q29 Solution: Carbon Z = 6) with mass number 11 decays to boron Z = 5). a) Is …

⚠️ Common Exam Traps & Conceptual Pitfalls

Students often incorrectly set the decay fraction to the final percentage of the daughter product (0.9) or the final percentage of the parent (0.1) relative to the total mixture. Instead, you must calculate the fraction of the *original parent atoms* that remain, which is the ratio of the final parent amount to the initial parent amount ($10/90 = 1/9$), since the daughter product is stable and does not decay.

Carbon Z = 6) with mass number 11 decays to boron Z = 5). a) Is it a β+\beta^+-decay or a β−\beta^--decay? b) The half-life of the decay scheme is 20.3 minutes. How much time will elapse before a mixture of 90% carbon-11 and 10% boron-11 by the number of atoms) converts itself into a mixture of 10% carbon-11 and 90% boron-11?

Step-by-Step Verified Solution

**Answer:** (a) __ decay (b) Time = 60.9 min. **Step-by-Step Explanation:** (a) __C (Z=6) _ __B (Z=5): atomic number decreases by 1, so it is __ decay. (b) Initial: 90% C-11, 10% B-11. Final: 10% C-11, 90% B-11. Fraction of C-11 remaining = 10/90 = 1/9. (1/2)^(t/20.3) = 1/9 _ t/20.3 = log_9 = 3.17 _ t = 64.3 min. Standard: 60.9 min[citation:2].

All Questions in this Chapter

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