Question

The unit of radioactivity is

• A. MeV
• B. curie
• C. a.m.u.
• D. joule

Hint:

Be careful to distinguish between units of energy (Joule, eV, MeV) and units of activity/radioactivity (Becquerel, Curie). Activity measures the 'how fast' of decay, while energy measures the 'how much' energy is released per decay.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Radioactivity (or simply activity) of a radioactive sample is defined as the rate at which the nuclei of its constituent atoms decay. It is a measure of the number of disintegrations per unit time.
Step 2: Detailed Explanation:
Let's analyze the units given in the options:
(A) MeV (Mega-electron Volt): This is a unit of energy, commonly used in nuclear physics. \(1 \, \text{MeV} = 1.602 \times 10^{-13}\) Joules. It is not a unit of decay rate.
(B) Curie (Ci): This is a traditional unit of radioactivity. It is defined as \(1 \, \text{Ci} = 3.7 \times 10^{10}\) decays per second. It is a valid unit for radioactivity.
(C) a.m.u. (atomic mass unit): This is a unit of mass, used for atomic and subatomic particles. \(1 \, \text{a.m.u.} \approx 1.66 \times 10^{-27}\) kg. It is not a unit of decay rate.
(D) Joule (J): This is the SI unit of energy or work. It is not a unit of decay rate.
The SI unit of radioactivity is the Becquerel (Bq), where 1 Bq = 1 decay per second. The Curie is a larger, non-SI unit that is still widely used.
Step 3: Final Answer:
Among the given options, only the curie is a unit used to measure radioactivity. Therefore, option (B) is correct.