Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Nuclear symbols are used to write nuclear equations for radioactive decay. Let's consider an example. Uranium-238 undergoes alpha decay to become thorium-234. (The numbers following the chemical names refer to the number of protons plus neutrons. ) In this reaction, uranium-238 loses two protons and two neutrons to become the element thorium-234. The reaction can be represented by this nuclear equation:. Answer: nuclear symbols
What are used to write nuclear equations for radioactive decay?