## Core Concept
The permissible radiation exposure per year for radiation workers is based on the guidelines provided by the International Commission on Radiological Protection (ICRP) and national regulatory agencies. These guidelines aim to limit the risk of radiation-induced harm to workers exposed to ionizing radiation in their occupation.

## Why the Correct Answer is Right
The correct answer, , refers to 20 millisieverts (mSv) per year. This is the recommended annual limit for occupational exposure to ionizing radiation for radiation workers, as per the ICRP guidelines. The sievert (Sv) is a unit of dose equivalent radiation, and 1 Sv = 1000 mSv. This limit is set to ensure that the risk of radiation-induced health effects, such as cancer, is kept as low as reasonably achievable.

## Why Each Wrong Option is Incorrect
* **Option A:** is significantly higher than the recommended annual limit for occupational exposure and does not align with guidelines from reputable organizations like the ICRP.
* **Option B:** might seem reasonable but is not the correct limit as per current guidelines for radiation workers.
* **Option D:** seems to imply a much lower limit than what is generally recommended for occupational exposure.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while 20 mSv/year is the limit for occupational exposure, efforts should always be made to keep exposure as low as reasonably achievable (ALARA principle). Additionally, it's crucial to differentiate between the general public and occupational exposure limits, with the former being significantly lower.

## Correct Answer Line
**Correct Answer: C. **