Task: Question Answering
Input (English): Context: Radioactive decay is the process in which the nuclei of radioactive atoms emit charged particles and energy, which are called by the general term radiation. Radioactive atoms have unstable nuclei, and when the nuclei emit radiation, they become more stable. Radioactive decay is a nuclearrather than chemicalreaction because it involves only the nuclei of atoms. In a nuclear reaction, one element may change into another. Click image to the left or use the URL below. URL: There are several types of radioactive decay, including alpha, beta, and gamma decay. In all three types, nuclei emit radiation, but the nature of the radiation differs. The Table 1.1 shows the radiation emitted in each type of decay. Type Alpha decay Beta decay Gamma decay Radiation Emitted alpha particle (2 protons and 2 neutrons) + energy beta particle (1 electron or 1 positron) + energy energy (gamma ray) Both alpha and beta decay change the number of protons in an atoms nucleus, thereby changing the atom to a different element. In alpha decay, the nucleus loses two protons. In beta decay, the nucleus either loses a proton or gains a proton. In gamma decay, no change in proton number occurs, so the atom does not become a different element. Q: If the radioactive element polonium (Po) undergoes alpha decay, what element does it become? A: From the periodic table, the atomic number of polonium is 84, so it has 84 protons. If it loses two protons through alpha decay, it will have 82 protons. Atoms with 82 protons are the element lead (Pb). The charged particles and energy emitted during radioactive decay can harm living things, but the three types of radioactive decay arent equally dangerous. Thats because they differ in how far they can travel and what they can penetrate. You can see this in the Figure 1.1. 
 Question: the type of radioactive decay that occurs when a nucleus emits an electron is
Output (English): beta decay.