In reactor design and operation, biological shielding is primarily installed to protect personnel from which emissions that dominate external dose around a nuclear reactor?

Introduction / Context:
Nuclear reactors emit several kinds of radiation. Biological shielding is the engineered barrier—commonly dense concrete, steel, water, and sometimes special polymers—built around the core and primary systems to protect workers and the public by attenuating penetrating radiation. Knowing which fields dominate exposure informs appropriate shield materials and thicknesses.

Given Data / Assumptions:

• A functioning reactor core with fission and activation sources present.
• Goal: reduce dose rates to below regulatory limits outside the shield.
• Consider common external fields in and around the containment or reactor building.

Concept / Approach:
Gamma rays (high-energy photons) and fast/thermal neutrons are highly penetrating and, therefore, are the principal contributors to external dose fields from reactors. Shielding design uses high-Z, high-density materials to attenuate gammas via photoelectric effect, Compton scattering, and pair production, while hydrogenous materials (water, concrete, polyethylene) slow and capture neutrons through scattering and absorption, often with boron additives to enhance capture.

Step-by-Step Solution:
1) Identify radiation fields near a core: neutron leakage and gamma fields from fission and activated materials.2) Determine which penetrate large distances: gammas and neutrons are most penetrating among routine fields.3) Conclude that biological shields are mainly designed for neutrons and gamma rays.

Verification / Alternative check:
Alpha and beta particles have limited range in air and are easily stopped by thin barriers (skin, paper, or a few millimeters of plastic/metal); they are serious as internal hazards but not the primary design basis for thick biological shields. X rays can be present in some equipment but are not the dominant core-related emissions.

Why Other Options Are Wrong:
X rays: not the principal reactor core emission; gamma rays are far more relevant.Alpha and beta: mainly internal hazards; penetration through shielding is small.Infrared: thermal radiation is not ionizing and is not the shielding design driver.

Common Pitfalls:
Confusing contamination control (alpha/beta) with shielding needs; overlooking the different materials required for gamma vs neutron attenuation.

Final Answer:
Neutrons and gamma rays