Nuclear & Radioactivity — Set 2

Correct Answer: A. Alpha radiation

Option A is correct because alpha particles ionize strongly due to their heavy mass and +2 charge. They lose energy quickly by collisions in air. High ionization usually comes with low penetration.

Correct Answer: D. Gamma radiation

Option D is correct because gamma rays have no charge. Charged particles like alpha and beta are deflected in fields. The direction of deflection depends on the sign of charge.

Correct Answer: C. Half of the nuclei decay

Option C is correct because half-life is the time for the number of undecayed nuclei to become half. It is a statistical measure for large numbers of nuclei. After each half-life, the remaining nuclei reduce by another factor of two.

Correct Answer: A. T1/2 = 0.693/lambda

Option A is correct because half-life equals 0.693 divided by the decay constant. A larger lambda means faster decay and smaller half-life. Decay constant has the unit of per second (s⁻1).

Correct Answer: D. A = lambda N

The correct answer is 'A = lambda N'. Option D is correct because activity equals decay constant times the number of undecayed nuclei. This shows activity decreases as N decreases over time. Activity is measured in decays per second.

Correct Answer: A. 1/8

Option A is correct because 30 days equals 3 half-lives of 10 days each. Remaining fraction is (1/2)^3 = 1/8. Half-life applies to the number of undecayed nuclei, not their size.

Correct Answer: C. Once-living organic materials

Option C is correct because carbon-14 dating works for materials that were once part of living organisms. Living things maintain carbon-14 while alive, then it decays after death. It is not suitable for very old geological rocks.

Correct Answer: B. 5730 years

Option B is correct because carbon-14 has a half-life of about 5730 years. This timescale suits dating of archaeological samples. Longer half-lives are used for dating much older objects.

Correct Answer: C. A heavy nucleus splits into smaller nuclei with energy release

Option C is correct because fission splits a heavy nucleus into lighter nuclei and releases energy. It often emits additional neutrons that can continue reactions. Uranium-235 is a common fissile material.

Correct Answer: C. Combining light nuclei to form a heavier nucleus

Option C is correct because fusion joins light nuclei into a heavier nucleus with energy release. It requires very high temperature to overcome repulsion between nuclei. The Sun produces energy mainly by fusion.