Final answer:
The nuclear equation represents an alpha decay where Thorium-230 emits a helium nucleus (alpha particle) and becomes Radium-226.
Step-by-step explanation:
The type of radioactive decay illustrated by the nuclear equation 230 Th → He + 238 Ra is alpha decay. In this process, the parent nucleus emits a helium nucleus, which is an alpha particle (consisting of two protons and two neutrons), and as a result, a new daughter nucleus is formed. The notation He indicates a helium nucleus (alpha particle) being emitted from Th (Thorium), thus transforming it into Ra (Radium).
The equation adheres to conservation laws regarding the number of protons and nucleons (neutrons + protons). The mass number of Thorium (230) decreases by four to become 226 (the mass number for Radium), while the atomic number drops from 90 (Thorium) to 88 (Radium), consistent with the release of a 4He (Helium) particle with a mass number of 4 and an atomic number of 2.