Nuclear & Radioactivity — Set 5

Correct Answer: B. Sievert (Sv)

Option B is correct because sievert measures biological effect of radiation dose. It includes weighting for radiation type and tissue sensitivity. Gray measures absorbed dose, while sievert relates to health risk.

Correct Answer: A. Monitor radiation exposure of a person

Option A is correct because a film badge records accumulated radiation exposure. It is worn by workers in radiation environments. Regular monitoring helps maintain safe dose limits.

Correct Answer: D. A radioactive noble gas

Option D is correct because radon is a noble gas and is radioactive. It can seep from rocks and soil into buildings. Long-term exposure is a health concern in poorly ventilated areas.

Correct Answer: B. Undergo fission with slow (thermal) neutrons

Option B is correct because uranium-235 can fission when it captures slow neutrons. This property helps sustain controlled chain reactions in many reactors. Uranium-238 is more abundant but is not fissile with slow neutrons.

Correct Answer: A. Uranium-238

Option A is correct because uranium-238 captures a neutron and changes through beta decays to plutonium-239. This is a standard breeding pathway in reactors. Plutonium-239 is fissile and can undergo fission with slow neutrons.

Correct Answer: A. D2O

Option A is correct because heavy water is D2O, where D is deuterium. Deuterium has one proton and one neutron in its nucleus. Heavy water can slow neutrons with relatively low absorption.

Correct Answer: B. Produce more fissile fuel than it consumes

Option B is correct because a breeder reactor generates additional fissile material during operation. It converts fertile material like uranium-238 into fissile material. This improves fuel utilization over time.

Correct Answer: C. Sustain a self-propagating chain reaction

The correct answer is 'Sustain a self-propagating chain reaction'. Option C is correct because critical mass ensures enough neutrons cause further fissions instead of escaping. It depends on shape, purity, and neutron reflection. Achieving criticality is essential for steady reactor operation.

Correct Answer: A. Net energy released or absorbed in the reaction

Option A is correct because Q-value is the energy difference between products and reactants. A positive Q means energy is released, and a negative Q means energy is absorbed. It is linked to mass difference using E = mc^2.

Correct Answer: D. Beta plus (β+) decay

Option D is correct because positron emission is beta plus decay. It occurs when a proton changes into a neutron inside the nucleus. A positron can annihilate with an electron to produce gamma photons.