Nuclear data units: the absorption/scattering cross-section of a nuclide is expressed in the unit “barn”, which is numerically equal to what area?

Introduction / Context:
Nuclear engineers quantify the likelihood of neutron–nucleus interactions using an effective area called the microscopic cross-section. The traditional unit is the “barn,” reflecting extremely small length scales in nuclear physics.

Given Data / Assumptions:

• We are comparing units of area and length; only one option expresses an area of the correct magnitude.
• Conversions use cgs units commonly seen in nuclear data tables.

Concept / Approach:
The barn is a convenient unit for cross-sections: 1 barn = 10^-24 cm^2. It provides tractable numbers when neutron capture or scattering probabilities are tabulated. While SI usage is increasing (1 barn = 10^-28 m^2), many datasets and exam references still present cross-sections in barns.

Step-by-Step Solution:
Recall definition: 1 barn = 10^-24 cm^2.Check units: options mixing centimeters and meters must be consistent with area.Select the area expression with cm^2 and the correct exponent, 10^-24.

Verification / Alternative check:
SI conversion: 10^-24 cm^2 = 10^-28 m^2. Some references use millibarn (mb) = 10^-3 barn; microbarn etc., but the base definition remains 10^-24 cm^2.

Why Other Options Are Wrong:

• 10^-12 cm and 10^-24 cm: lengths, not areas.
• 1 angstrom: a length (~10^-8 cm), not area.
• 10^-16 m^2: equals 10^-12 cm^2, not the barn value.

Common Pitfalls:
Confusing area with length units; mixing SI and cgs without converting exponents properly.

Final Answer:
10^-24 cm^2