Final answer:
When uranium-238 emits an alpha particle, it becomes thorium-234, due to a decrease in both its atomic number and mass number.
Step-by-step explanation:
If a radioactive uranium-238 atom gave off an alpha particle, the atom would become thorium-234. This is because an alpha particle consists of two protons and two neutrons. When uranium-238 emits an alpha particle, its atomic number decreases by 2 (from 92 to 90) and its mass number decreases by 4 (from 238 to 234), becoming thorium-234. This type of radioactive decay is a common process in nuclear physics, illustrating how one element can transform into another.
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is considered radioactive. Three of the most common types of decay are alpha, beta, and gamma decay. The weak force is the mechanism that is responsible for beta decay, while the other two are governed by the electromagnetism and nuclear force.