The SI unit of absorbed dose of radiation is:`
The core concept here is understanding the difference between absorbed dose and equivalent dose. Absorbed dose measures the amount of energy deposited in a mass of tissue, while equivalent dose considers the biological effect of different types of radiation. The SI unit for absorbed dose is gray (Gy), which is equal to one joule per kilogram. The older unit was the rad, where 1 Gy = 100 rad.
Now, looking at the options, the correct answer should be gray. The other options might include sievert (which is for equivalent dose), roentgen (for exposure), and perhaps curie or becquerel for activity. Let me make sure: roentgen is an older unit for exposure, measured in coulombs per kilogram in SI. Sievert is indeed for equivalent dose, which is adjusted by a radiation weighting factor. So the wrong options are all related but not the correct SI unit for absorbed dose.
The clinical pearl here is to remember that gray is for absorbed dose, and sievert is for equivalent dose. A mnemonic could be G for gray (absorbed) and S for sievert (equivalent). Also, in exams, they often mix up these units, so it's crucial to distinguish between them. The correct answer is gray (Gy).
**Core Concept**
The SI unit of absorbed radiation dose quantifies energy deposited in a medium, specifically one joule per kilogram (J/kg). This differs from units for equivalent dose (which account for radiation type) or activity (which measures radioactive decay).
**Why the Correct Answer is Right**
Gray (Gy) is the SI unit for absorbed dose, defined as 1 joule of energy absorbed per kilogram of mass. It directly measures the physical energy deposition in tissue, making it critical in radiology, radiotherapy, and radiation safety calculations.
**Why Each Wrong Option is Incorrect**
**Option A:** Sievert (Sv) measures *equivalent dose*, which incorporates biological effectiveness of different radiation types.
**Option B:** Roentgen (R) quantifies *exposure* (ionization in air), not absorbed dose in tissue.
**Option C:** Becquerel (Bq) measures *radioactive activity* (decays per second), unrelated to energy absorption.
**Clinical Pearl / High-Yield Fact**
Remember: **Gy = Gray (Absorbed)**, **Sv = Sievert (Equivalent)**. Confusing these units is a common exam pitfall. For example, in radiotherapy, tumor doses are prescribed in Gy, while occupational exposure limits are set in Sv.
**Correct Answer: C. Gray**