Nuclei — Previous-Year Questions

Q1. A radioactive sample has T_½ = 10 minutes. Initial activity is 80 Bq. After 30 minutes, activity is:

Q2. Decay constant of an isotope with half-life 2 years:

Q3. In α-decay, the daughter nucleus has:

Q4. In β⁻-decay, the nuclear mass number A:

Q5. Which radiation is MOST penetrating?

Q1. A radioactive sample has half-life 5 years. After 20 years, fraction remaining:

Q2. A sample's activity drops from 800 Bq to 100 Bq in 30 minutes. Half-life:

Q3. If a radioactive sample has a half-life of 8 hours, after 24 hours the activity is reduced by a factor of:

Q4. Carbon-14 in a bone is 1/16 of that in living tissue. Bone's age (T_½ = 5730 yr):

Q5. If decay constant of a nucleus is 0.1/day, its half-life:

Q1. A semi-log plot of N(t) (ln N vs t) for radioactive decay gives:

Q2. After how many half-lives does the activity drop to 1% of its initial value?

Q3. In a parent-daughter decay chain at secular equilibrium:

Q4. If 75% of a sample has decayed, the elapsed time in terms of T_½ is:

Q5. On a decay curve, the time required for activity to drop to e⁻¹ (≈ 37%) of initial is:

Q1. Mass defect of a nucleus is 0.0529 u. Binding energy is:

Q2. Binding energy per nucleon peaks near:

Q3. Mass defect of ⁴₂He: 2(m_p + m_n) − m_He = 0.0303 u. Binding energy:

Q4. Why is fusion of light nuclei energy-releasing?

Q5. Binding energy is the energy required to:

Q1. In the reaction ²³⁵U(n, fission), the missing particle in ²³⁵U + n → ¹⁴⁴Ba + ⁸⁹Kr + ?n + Q is:

Q2. In the reaction ¹⁴N + α → X + p, X is:

Q3. Q-value > 0 means:

Q4. Rutherford's 1919 transmutation of nitrogen was:

Q5. Conservation laws in nuclear reactions include:

Q1. In the fission ²³⁵U + n → ¹⁴⁴Ba + ⁸⁹Kr + xn + Q, x is:

Q2. Approximate energy released per fission of U-235:

Q3. Moderator in a thermal nuclear reactor is used to:

Q4. Why is U-235 used in reactors rather than U-238?

Q5. Critical mass is:

Q1. Approximate energy released per D-T fusion:

Q2. Energy source of the Sun is:

Q3. Why does fusion need such high temperatures?

Q4. Energy per nucleon released in fusion vs fission:

Q5. Lawson criterion for fusion involves:

Q1. Energy released when 1 g of matter is fully converted to energy:

Q2. Mass defect equivalent to 1 MeV is:

Q3. 1 u in MeV/c² is:

Q4. Pair production (γ → e⁺ + e⁻) requires minimum photon energy:

Q5. Energy of each γ when an electron and positron at rest annihilate: