## Core Concept
Radioisotopes are atoms that contain an unstable nucleus and undergo radioactive decay, emitting various types of radiation. The types of radiation commonly emitted include alpha (α), beta (β), and gamma (γ) radiation. Understanding the characteristics of each type of radiation is crucial in nuclear physics and medicine.

## Why the Correct Answer is Right
Gamma (γ) radiation is a type of electromagnetic radiation, similar to X-rays but with higher energy. Alpha (α) particles are high-energy helium nuclei, and beta (β) particles are high-energy electrons. These are all forms of ionizing radiation that can be emitted by radioisotopes. However, "sound waves" are not a form of radiation emitted by radioisotopes; they are a type of mechanical wave that requires a medium to travel and are not related to radioactive decay.

## Why Each Wrong Option is Incorrect
* **Option A:** Alpha (α) particles are indeed emitted by radioisotopes and are a form of ionizing radiation.
* **Option B:** Beta (β) particles, which include beta minus (electrons) and beta plus (positrons), are also emitted by radioisotopes.
* **Option D:** Gamma (γ) rays are high-energy electromagnetic radiation emitted by radioisotopes.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the type of radiation emitted determines the radioisotope's applications and safety considerations. For example, gamma radiation is used in nuclear medicine for both diagnosis (e.g., PET scans) and treatment (e.g., radiation therapy), while alpha particles are used in certain cancer treatments due to their high ionization energy but short range.

## Correct Answer Line
**Correct Answer: . sound waves**