Half life of cobalt-60: September 2011
**Core Concept**
The half-life of a radioactive substance is the time required for half of the unstable atoms in a sample to undergo radioactive decay. **Cobalt-60** is a synthetic radioactive isotope of cobalt with a variety of applications, including in medicine and industry. Its half-life is a critical parameter for understanding its handling, storage, and utilization.
**Why the Correct Answer is Right**
The correct half-life of **cobalt-60** is 5.2713 years. This value is a fundamental physical constant that determines how long it takes for the radioactivity of a **cobalt-60** source to decrease by half. This knowledge is essential for calculating the activity of **cobalt-60** sources over time, which is crucial for medical, industrial, and research applications.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it does not match the known half-life of **cobalt-60**.
**Option B:** Incorrect as it also does not correspond to the established half-life of **cobalt-60**.
**Option D:** Similarly, this option is incorrect as it does not align with the verified half-life of **cobalt-60**.
**Clinical Pearl / High-Yield Fact**
Remembering the half-life of **cobalt-60** is important for radiation safety and for the use of **cobalt-60** in radiotherapy. The half-life of a radioactive substance is a key factor in determining its suitability for various medical and industrial applications.
**Correct Answer:** C. 5.3 years