Nuclear units and constants: The symbol MeV (mega–electron-volt) is a unit of which physical quantity?

Introduction / Context:
In nuclear and particle physics, energies are often quoted in electron-volts and their multiples (keV, MeV, GeV). Recognizing what MeV measures avoids confusion with activity units or electrical units.

Given Data / Assumptions:

• 1 eV is the energy gained by an electron accelerated through a potential difference of 1 volt.
• 1 MeV = 10^6 eV.

Concept / Approach:
MeV quantifies energy. Radioactivity is measured in becquerel or curie; potential difference is measured in volts; exposure/dose have different units (gray, sievert). Thus, MeV refers specifically to energy, commonly used for binding energies, decay Q-values, and reaction thresholds.

Step-by-Step Solution:
Recall definition: eV is an energy unit.Scale to MeV for nuclear magnitudes.Therefore, MeV is a unit of energy.

Verification / Alternative check:
Mass–energy equivalence frequently uses MeV (e.g., 1 amu ≈ 931 MeV of energy equivalent).

Why Other Options Are Wrong:
Radioactivity uses Bq or Ci, not MeV. Potential difference uses volt (V). “None of these” is incorrect.

Common Pitfalls:

• Confusing “per nucleon” energies with total reaction energies; both are energy but differ in normalization.
• Mixing activity (decays per second) with energy scales.

Final Answer:
Energy