Final answer:
Alpha particles are represented by alpha (α) and are helium-4 nuclei. Beta particles are represented by beta (β) and are electrons. Gamma rays are represented by gamma (γ) and are a form of electromagnetic radiation.
Step-by-step explanation:
The lowercase letters alpha, beta, gamma, and theta are often used to represent different types of nuclear radiation. These letters come from the Greek alphabet and were chosen because they are the first four letters. Alpha particles, represented by alpha (α), are helium-4 nuclei. Beta particles, represented by beta (β), are electrons. Gamma rays, represented by gamma (γ), are a form of electromagnetic radiation similar to x-rays, but more energetic. Theta (θ) is not specifically used to represent a type of nuclear radiation.