**Core Concept**
The half-life of a radioactive substance is a fundamental concept in nuclear medicine and radiation biology. It refers to the time required for the radioactive decay of a substance to reach half of its initial radioactivity. In this case, the question is asking about the half-life of Cobalt-60 (Co-60), a radioactive isotope commonly used in medicine for cancer treatment and in industry for sterilization.

**Why the Correct Answer is Right**
Cobalt-60 (Co-60) is a radioactive isotope with a half-life of approximately 5.2713 years. This means that every 5.27 years, the radioactivity of Co-60 decreases by half. The half-life of Co-60 is due to the beta decay of the isotope, where a neutron in the nucleus is converted into a proton, an electron, and a neutrino. This process is facilitated by the weak nuclear force and results in the emission of beta particles (electrons) from the nucleus.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not specify the half-life of Co-60. Without knowing the specific half-life, it is impossible to determine if this option is correct or not.
* **Option B:** This option is incorrect as it is not a commonly recognized or documented half-life value for Co-60.
* **Option C:** This option is incorrect as it is not the correct half-life value for Co-60.

**Clinical Pearl / High-Yield Fact**
The half-life of a radioactive substance is a critical parameter in radiation therapy and nuclear medicine, as it determines the duration of treatment and the potential for radiation exposure to patients and healthcare workers.

**Correct Answer: C. 5.2713 years**